Histology Review & Colored Atlas part 1 [1]

Table of contents :
Cover
......Page 1
Contents
......Page 4
Introduction......Page 5
Cell Membrane......Page 7
Endoplasmic Reticulum......Page 11
Golgi Apparatus......Page 13
Lysosomes......Page 14
Ribosomes
......Page 15
Cilia......Page 16
Microtubules......Page 17
Microvilli......Page 18
Cell Inclusions......Page 19
Nucleus......Page 20
Nuclear Sap......Page 21
Chromatin......Page 22
DNA......Page 23
RNA......Page 24
Mitotic Cell Division......Page 25
Meiotic Cell Division......Page 27
Karyotyping......Page 28
Chromosomal Aberrations (Abnormalities)......Page 30
Sex Chromosomes......Page 31
Modes Of Inheritance......Page 32
Blood Groups......Page 33
Red Blood Corpuscles......Page 35
Leucocytes......Page 38
Types Of Leucocytes......Page 40
Neutrophils Or Polymorphonuclear......Page 41
Eosinophil......Page 42
Basophil......Page 43
Large Lymphocytes......Page 44
T -Lymphocytes......Page 45
B - Lymphocytes......Page 46
Platelets......Page 47
Myeloid Tissue (Red Bone Marrow)......Page 49
Erythropoiesis......Page 50
Granular Leucocytes
......Page 52
B- Lymphocytes
......Page 53
T -Lymphocytes
......Page 54
Monocytes
......Page 55
Platelets
......Page 56
Simple Squamous......Page 57
Simple Columnar......Page 58
Pseudo-stratified......Page 59
Stratified Epithelium
......Page 60
Stratified Squamous......Page 61
Stfatified Columnar Ciliated......Page 62
Transitional Epithelium......Page 63
Rules......Page 64
Classifications
......Page 65
Tubular Glands......Page 67
Neuro-Epithelium......Page 68
General Characteristics Of Epithelial Tissue......Page 69
Functions Of Epithelial Tissues......Page 70
Fibroblast......Page 71
Mesenchymal Cells......Page 72
Reticular Cells......Page 73
Mast Cells......Page 74
Free Macrophages......Page 75
Reticular......Page 76
Loose Areolar......Page 77
Adipose......Page 78
Yellow Elastic......Page 79
White Collagenous......Page 80
Mucoid (Mucous)......Page 81
Chondrocytes......Page 82
Hyaline Cartilage......Page 83
Elastic Cartilage......Page 84
Osteoblast......Page 85
Osteoclasts......Page 86
Com pact Bone......Page 87
Spongy Or Cancellous Bone......Page 88
Ossification Of Bone......Page 89
Smooth Muscles......Page 91
Skeletal Muscles......Page 92
Cardiac Muscle......Page 94
Purkinje Fibres......Page 95
Nerve Cells......Page 96
Axon......Page 97
Myelin Sheath......Page 98
Synapse......Page 99
Nerve Ganglia......Page 100
Neuroglia......Page 101
Nerve Endings......Page 103
Receptors......Page 104
Neuro-Muscular Junctions......Page 106
Keratinocytes......Page 107
Dermis Of The Skin......Page 108
Sweat Glands......Page 109
Hairs......Page 110
Medium - Sized Artery......Page 111
Medium - Sized Vein
......Page 112
Umbilical Artery......Page 113
Arterio Venous Anastomosis
......Page 114
Lymph Nodes......Page 115
Spleen......Page 116
Thymus......Page 118
Macrophage System......Page 120
Trachea......Page 121
Bronchial Tree......Page 122
Type I Pneumocytes......Page 123
Blood Air Barrier......Page 124
Foetal Lung......Page 125
Slide Photomicrographs......Page 127

Citation preview

Review And Colo ured Atla s Of

H IS TO LO G Y For Med ical, Dent istry , Phar mac y Vete rinar y And Post grad uate Part 1

By Professor

Zak aria Abd -Eih ami d Chairman Of Histology Department

Facu lty Of Medicine Cair o University

All Rights Reserved To The Author

·,

Preface The purpose of this book is to provide medical students with a concised but fully illustrated account of normal human histology. It is hoped that this coloured illustrated book will be of great value to supply medical students with labelled photomicrographs from their actuallabo rato ry slides. They may place these photomicrographs beside their microscop es while viewing sections of normal histological or abnormal pathological materials • This book is not intended to replace comprehensive text books of histology but rather to complement them and to add more details about the structure and functions of organs. The content and design of· this book have been chosen to make it easy to use both as a short text and as a laboratory guide. It is hoped tha~ this illustrated text will be of great value to fulml the requirements of medical, dentistry, pharmacy and veterinary students. It also should have a wide appeBI for the post graduate .medical members and Primary Fellowship. examinations. In presenting this book, I. should like to express my appreciation for the help and encouragement that I have received from my wife. \

Prof. Zakaria Abd-ELhamid

Contents Page Intro ducti on •. . •. •. ••. . . •• . ••. .• . •. .. . . .•• . .•. •• . •. . . . . .• •• 1 The Cell .••.••..•.••.•••.•...••.••••.••....•..•.•.•......•.• 3 •••••••.••••••••••••••••••.••.•.•••••..••••••••••••••• :tl .Blood ••• •••••••. •••• •. •••••••••• •••••••. •••••••••••••••• ••••. 31 ~11etics

Epithelial Tissue • . •. . . ••. . ••• . . ••••••. ••. •. •••. ••. ••. •. •. . 53 Connective Tissue Prop er ..•••....•••.••..••••.••••••.• 67 Cartilage •. . •. •. ••••••. . . ••••••. •. ••••. . •. •••••. •••• •••. ••••. 78 Bone .•••••.• ••••• •• •• ••• •• •. •. ••• . .•.•.• .. .•. . •.• . .• ••• . . ••. . 81 Muscular Tissue ....•.• ....... ....... ....... ....... •...... 87 Nervo us Tissue •.•••••.•••••••••..•••..•..•••••.••..•.••••. 92 Neuro glia •. ••. ••••• ••. . ••••. •. • •••••••. . . •• ••. . •. •. •. . . . . ••• 97

Degeneration Of Neurones •••.•...•...••.•.•.••.•••.•. 99 Recep tors •••••.••••••.••.••••..•••••••••.••••••••.••.•·•••. 100

Neuro-Muscular Junct ions ••••••..••.••.••••.•••••••. 102 Skin ••• •••• . . •. . •.• . ••• ••• •. . •. ••• ••. •••••. •• •• ••• . •• •• •• ••••. 103 Blood Vascular System ••...•.•.•...•..•..•..••.•••••••• 107 Lymphatic System ••••.••.••.••••.•.••••••.•••••.•••••••. 111 Reticulo-Endothelial System ••.•........•..•.••••.••.•. 116 Respiratory System ••••.•...•.•••.....•..•.•••.•..••••••• 117 Slide Photo micro graph s .••.•.• ~ •....•.•.••....••••...•• 123

Introduction types of To stud y Histology, it is impo rtant to know the used in Histology. microscopes, microtechniques and the different stains

Types Of Microscopes: of illumination. 1. Light Microscope, in which light is the source rons is the source 2. Electron Microscope ElM , in which a beam of elect of illumination.

Types Of Microtechniques: 1. 2. 3. 4.

The para ffin technique, (is the common method). The celloidin technique, (is the mos t perfect method). The freezing technique, (is the most rapid method). The tissue culture (used in chromosomal study)

Types Of Stains Used In Histology: Eosin; to stain the cytoplasm with red colour. Hematoxylin; to stain the nucleus with blue colour. Cells. Leishman; to stain nuclei and cytoplasm of blood Trypan Blue. The phagocytic Cells can be stained with vital stains as al stain as The Reticulocytes of blood can be stained with supra-vit Brilliant Cresyl Blue. as Toluidine 6. Mast Cells can be stained with a metachromatic stain Blue. with Sudan 7. Fat Cells can be stained orange with Sudan 3, black Black or black with Osmic Acid. Stain. It stains 8. Trichrome Stain gives 3 colours as Mallory ic fibres red. collagenous fibres blue, smooth muscles yellow and elast

1. 2. 3. 4. 5.

-1-

""-- Mic ro viii i Secretion Gra nul e Golgi App ara tus Cell Me mb ran e ·I

Adh eren t Jun ctio n

I

' I'

Pig men t Basal

Infoldin~

Sm oot h E.ndoplasmic ' Reticulum

Cell Co mp on en ts

Th e Cell nisms. Cells are the structural units of all living orga The cell is composed of two basic parts: 2- Nucleus 1- Cytoplasm The cytoplasm is composed of: ein, fat, carbohydrate, 1. Cytoplasmic matrix which is a solution of prot enzymes and minerals. of carbohydrates, lipids 2. Cytoplasmic inclusions which are deposits and pigments. 3. Cytoplasmic organoids or cell organelles. bules, Microfilaments 4. Cytoplasmic Skeleton : which are : Microtu and Intermediate Filaments.

Cell Organelles are of two types: They are t9e small organs of the cell, they by membranes as: a) Membranous Organelles which are covered oth endoplasmic Cell membrane, Mitochondria, Rough and smo xisomes, Coated reticulum, Golgi apparatus, Lysosomes, Pero vesi cles and Endosomes. are not covered by b) Non- Membranous Organelles which membranes as : Ribosomes

1- Th e Cell Me mb ran e All cells are enveloped by a limiting ' cell membrane. It is also called plasma membrane or plasmalemma. It is not visible by the ligh t microscope. It has a tri-lamellar appearance (Formed of 3 layers) under the Electron Microscope (E/M ).

-3-

Molecular Structure Of Cell Membrane: It is Formed Of Lipids, Proteins and Carbohydrates. 1. The Lipids are phospholipids and cholesterol. - Each phospholipid molecule fs formed of a.) Hydrophilic charged heads. ·b) Hydrophobic non-charged tails. ·- Cholesterol molecules are present close to the inner cytoplasmic aspect of the cell membrane 2. The Protein components of the cell membrane are of 2 groups: a) Integral or intrinsic protein, formed of small and large molecules. b) Peripheral or extrinsic protein formed of continuous and non-continuous protein, loosely attached to the cytoplasmic surface. 3. The Carbohydrate Components are linked to the surface protein to form glycoprotein, and are linked to the surface lipid to form glycolipid - Glycolipids and Glycoproteins for_m the Glycocalyx or Cell Coat. It is rich in cell receptors which perform different functions.

Different Types Of Junctions Between Cell Membranes Adjacent epithelial cells are adherent to each other due to: 1. The binding action of their cell coats. 2. Presence of calcium ions in their ·inter-cellular spaces. 3. Presence of the following types of cellular junctions: a) Tight junction in which there is complete fusion between two adjacent cell membranes. The distance between the two cell membranes is zero.

-4-

Tight .

Junction

Adberens Junction Desmosomal Junction

b) Adh erin g Junc tion in which the distance between the two cell membranes is 20 nano mete r. c) Gap Junc tion in which there is narr ow channels between two adja cent cells. d) Desmosomal Junc tion in which the two adja cent cell membranes the by thic ken ed are cond ensa tion of cyto plas mic micr ofila men ts. e) Hem ides mos oma l Jun ctio n which is a spot-like junc tion with a of stru ctur e the half-desmosome. It is present between the basal surface of epit heli al cells and thei r underlying basement membranes as in skin.

Gap Junc tion

Hemidesmosom~

Functions Of The Cell Membrane into and out of the cell It regulates the passage of certain mat erials through the following mechanisms: r weight substances. 1. Passive Diff usio n of ions and of low molecula which is supp lied by 2. Active Tran spor t of materials using energy mito chon dria . action of cell membrane 3. Selective Transport of materials through the 4. 5. 6. 7.

receptors. of Phagocytosis or Tran spor t of solid materials by the process Endocytosis. of Pinocytosis or Tran spor t of liquid materials by the process Endocytosis. Exocytosis. Release of residual materials by the process of s the K + more Sod ium -Pot assi um Pum p Fun ctio n, this keep entrated out";.-~,. concentrated inside the cell and the Na + more conc the cell.

-5-

8. Specific Functions Of The Cell Coat or Glycocalyx: a) Cell adhesion helping in holding adjacent cells together. b) Cell Recognition helping the cells to recognize each other. c) Formation Of Cell Immunity through formation of antibodies on the cell surface. d) Formation Of Cell Allergy through antigen- antibody reactions to protect the cell against harmful agents. e) Glycocalyx is rich in Cell receptors. These receptors regulate the enterance of hormones, enzymes, drugs, bacteria, chemicals and viruses to the cell. 9. Special Cell Membrane Functions: the cell membrane may be modified to form the following structures:a) Micro- villi which are cell membrane projections on the surface of certain columnar cells to increase their absorptive functions. Microvilli contain cytoplasmic micro filaments. b) Cilia which are membrane projections in certain columnar cells, they contain 20 cytoplasmic microtubules. c) A Flagellum which is a cell membrane projection. It forms the tail of a spermatozoon. d) Basement Membrane or Basal Lamina which is formed by the glycoprotein of the cell membrane and the underlying collagen. e) Cellular Junctions: The cell membranes of certain adjacent cells are modified to form different types of junctional complexes between cells. They have important functions between certain cells. f) Cell Membrane Infoldings. Invagination of the cell membrane of certain cells form infoldings to facilitate active transport of some ions, as in kidney cells, rods and cones cells of retina.

-6-

2-

Mit och ond ria

They are mem bran ous cell organelles, They give energ y to ali cellular funct ions . .r·~"M;W · Unde r light micro scope ( L.M. ), they "' appe ar as rods, granu les or filaments. Unde r Elec tron Micr oscop e (E.M .) they appe ar as oval bodi es with doub le mem brane s, the outer is smoo th and the

dria

E/M Of Mitochon inner is folde d. Stains Blue with iron hema toxyl in and Green with Janu s green . ions of cell, Number: It increases or decreases according to the funct a liver cell conta ins abou t 2000 mito chon dria.

hydr ate, Mito chon drial matr ix is form ed of prote in, fat , carbo and Zinc vitamins, respi rator y enzymes, DNA , RNA , Ca, Mg granules which act as catal ysts. Mito chon dria are motile, contr actile and can divide. Func tions Of Mito chon dria: r hous e for They supp ly energy to all cellular activities (act as powe the cell). phor ylati on Their enzymes perfo rm -all cellular oxidative phos proce sses. mine rals. They regul ate the meta bolis m of calcium and other actio n and They supply energ y for prote in synthesis, musc ular contr trans port of mate rials acros s the cell mem bran e.

3-

Endoplasmic Reticulum

They are of TWO types : omes . a ) Roug h Endo plasm ic Retic ulum covered with ribos ribos omes . b) Smo oth Endo plasm ic Reticulum not cove red by

-7-

It is formed of communicating flat tubules with rough surfaces due to attached ribosomes. It gives the cytopla sm its basophilic appearance. It is more demonstrated in protein synthetizing cells as plasma cells, pancreatic cells, fibrobla st and osteoblast cells. Rough Endopla smi c Reti culum

Functions:

Protein synthesis with the aid of their attache d ribosomes. Protein segregation, storage, packaging and delivery.

b- Smooth Endoplasmic Reticulum It is formed of communicating tubules with smooth surface because there is no ribosomes. It shows no cytopla smic basophi lia. It is more demons trated in lipid forming cells as liver and endocrine cells. Functions:

Lipid synthesis. Glycogen storage. Smoo th Endopl as mic Reticulu m Detoxi ficatio n of harmfu l substances. HCl formati on in stomac h cells. Regulafe calcium distribu tion during muscular contrac tion.

-s--

4- Golgi App arat us with Definition : It is a memb ranou s organelle which is concerned secretory condensation, packaging and chemical modification of the products of the cell. rk By Light Microscope (L.M.) It appears with Silver stain as a netwo cells. beside the nucleus in secretory cells and aroun d the nucleus in nerve flat By Elect ron Microscope (E.M ) It appears as small sacs called saccules or as large macro-vesiCles or as small micro-vesicles. funct ions Of Golgi Appa ratus

1. 2. 3. 4. 5.

Cond ensat ion and packaging of secretory products of the cell. cts. Its transferase enzyme adds carbo hydra tes to certain cell produ Its sulfatase enzyme adds sulfates to certain cell produ cts. tion. It shares in cell membrane forma tion to keep it in a good condi lysosome It shares the endoplasmic reticulum in the process of forma tion.

'

.

• 1 '"

.r- 1' . Golgi App aratu s .. In Nerve Cells

E/M Of Golgi Appar atus

-9-

5- Lysosomes Defini tion : They are membr anous organelles concerned with intracel lular digestion of food and foreign substances.

/

I

Primary Lysosome

By L.M.: They appear as dark granules with acid phosphatase stain or by fluorescence microscope.

· . Residual Body

.' Mul tivesicula r , Bodies

By E.M: 1- Primary lysosomes appear as homogeneous rounded small bodies.

.

2- Secondary lysosomes appear as heterogeneous small bodies. Conten ts: They are rich in hydroly tic enzyme s as lipases, proteases, nucleotidases and acid phosphatases.

Mitochondrion

0 igin: Thro ugh Trans - Golgi Networ k Process, lysosomal enzymes are formed and modffied in endoplasmic reticulum and Golgi bodies. Fate: 1. Remain as primary lysosom es. 2. Fuse with the phagocytic bodies to be transfo rmed into Second ary lysosom es. 3. Lysosomes change into Multivesicular Bodies which represent fusion of the residual bodies.

Functions Of Lysosomes 1. Digestion of the phagocytosed substances. 2. Defending the body by digesting the invadin~ organisms.

-10-

3. Digestion of the useless mitoch ondria and endoplasmic reticulum. 4. In kidney, they hydrolyse the filtered protein helping in their reabsor ption. 5. In thyroid gland they loosen their inactive hormones to be active. 6. In blood leucocytes, they destroy the invading organis ms. 7. They facilitate penetra tion of sperms to ova. 8. They are concerned with the post-mo rtem changes in the cells after death.

6. Peroxisomes: They are small organelles that contain several 7. 8.

enzymes involved in lipid metabo lism. Coated Secretory Vesicles: They contain digestive enzymes and are called Zymogen GranuJes. Endosomes: They are lipoprotein microbodies present under the cell membrane. They facilitate interance of molecules by a selective mechanism called Recepto r Mediat ed Endocytosis after formati on of Ligand s.

Ribosomes·

Deimit ion: They are cytoplasmic basophilic structures responsible for protein synthesis. SWning : Stained blue by hematoxylin and methylene blue. Sites Of Their Format ion: In the nucleolus. §nuctu re: Formed of ribonuc leoprot ein = RNA + Protein . Differe nt Forms Of Ribosomes In The Cytoplasm: a) Free Ribosomes giving the cytoplasm its basophilic appearance. b) Attadle d Ribosomes to the outer surfaces of rough endoplasmic reticulum. c) Form Isolated Bodies as Nissl's granules in nerve cells. d) In The Form of Spiral Structu res called polysomes. e) In The Form of Fragme nted Structu res called microsomes. ElM Pictures: Formed of 2 subunit s with a polypeptide chain between its units. -11-

Functions Of Ribosomes Free ribosomes synthesize cytoplasmic protein. Attached ribosomes with the rough endoplasmic reticulum form the secreted protein in the form of hormones and enzymes.

Centrioles Each dividing cell contains 2 tubular structures called centrioles. They are not present in mature nerve cells and erythrocytes.

ElM Of One

Staining: Iron hematoxylin. Centriole E/M Structure: Each centriole is a tubular structure, the wall of each tube is formed of 27 microtubules which are arranged in 9 groups, each group is formed of 3 microtubules. Functions. Of Centrioles: 1. During cell division they form the Microtubular Organizing Centre (MTOC) which form mitotic spindle. 2. They form cilia and flagella. .,__ T.S.

Cilia

And

They are hair-like processes extending from the free surfaces of certain cells.

y

c

L.S . In Cilia

ElM: Eachciliumisformedof: 1. A basal body similar to the structure of a centriole, formed of 27 microtubules arranged in groups, each group of 3 microtubules.

. -~ Microvilli

My ' .

o

Basal

Body

ElM Of Cilia And Microvilli - ·12-

2. A Shaft Formed of 18 peripheral microtubules arranged in 9 groups, each group of 2 micro tubules. In the centre there is 2 more microtubules. 3. A Roode t formed of 7 microtubules embedded into the cytoplasm of the cell. Functions Of Cilia: They push fluid or small bodies in one direction. Th~~ act as photoreceptors in the rods and cones of

reti~a.

Flagella They are similar to the cilia in their structure but they are longer. A single flagellum form the tail of a mature spermatozoon.

Cytoskeleton Of The Cell These are the microtubules, microfilaments and the intermediate fllaments. They form the shape of the cell. They play an important role in cytoplasmsic and cellular movements.

1 - Microtubules They are present in all kinds of cells. They are cylindrical filame ntous structures about 24 nm in diameter. They are formed of protein known as tubulin. They appear as tiny circles in cross section. Most of the microtubules are anchored in a region near the centriole. They are of variable lengths and are sufficiently elastic to bend without breaking. -13 -

Microtubules (E/M )

Functions of Micro tubules: They act to some extent as a skeleton for the cells. They facilitate the transport of various particles throughout the cytoplasm. They are concerned with the movement of cilia. They play an important role during cell division.

2-

Microfilaments

The cytoplasm contain the following microfilaments:1. Actin Filaments or thin ftlaments which are found mainly in muscles. 2. Myosin Filaments or thick ftlaments which are also found in muscles. 3. Intermediate Filaments: As keratin in epithelial cells, Vementin in fibroblasts, Dysmin in muscle cells, Neurofilaments in nerve cells and Glialfilaments in neuroglia. Functions Of Microfilaments:1. In muscle cells are responsible for contractions. 2. In certain blood cells the y help in their amoeboid movemen ts. 3. In blood platelets they help in retraction of blood clot. 4. In dividing cells the y form a

Microfilaments (E/M)

contractile ring which help in the separation of the dividing cells . 5. In microvilli of certain cells, they play a role in their contraction, elongation and shortening.

Microvilli They are finger like projections on the surface of certain cells of the body, for example; cells of the intestine, liver and kidney. They are formed of actin microfilaments covered with the cell membrane. -14-

They increase the efficiency of absorpti on and the surface area of the cell.

The Cell Inclusions

·.·.. ... :.

These are accumul ated molecules of:

... ,;~

..._·:

1. Carbohy drates in the form of glycogen

granules mainly in muscle and liver cells. They can be stained red with Best carmine stain . 2. Lipids in the form of fat droplets in fat cells, liver and adrenal cortex cells . They can be stained with Sudan 3 or Sudan black or with Osmic acid. 3. Pigment s which are of two types . a) Endogen ous Pigment s which are synthesized by the cells as: Haemog lobin which is formed by the red blood corpuscle s. Melanin which is formed by the melanocytes. Lipofusc in which are the accumul ated non-digested lysosomes in nerve and cardiac cells. b) Exogeno us Pigment s which come from outside to be accumul ated in the cells as: Carotene , carbon and dust particles , silver and lead paritcles and the tattoo marks. Liver

s d Cor :Y •

••

•• •

• Fat Granule s in fat Cells Osmic Stain

Glycogen Granules In Liver Cells (Best's Carmine Stain) -15-

The Nucleus Definition: It is a rounded or elongated structure present in all mammalian cells except the red blood corpuscles. It plays an important role in heredity, in cell division and in controlling all cellular functions. Number: Usually each cell contains one nucleus. Two nuclei may be present in some liver cells and some superficial cells of the transitional epithelium, while many nuclei are present in the f"''\teoclast cells of bone and in skeletal muscle cells. Size: The nucleus may be: small, medium sized or large. Shape: There are various shapes for the nuclei. They may be rounded, oval, flattened, rod-shaped, . bilobed (horse shoe), lobulated, kidney-shaped, or segmented. Position: The nucleus may be central, eccentric, peripheral or basal in position. Staining: The nucleus Is a basophilic structure. It can be stained with any basic stain as hematoxylin because it is rich E/M Of A Nucleus in nucleic acids (DNA + RNA). Structure: The nucleus consists of FOUR Components: 1. 2. 3. 4.

Nuclear membrane or nuclear envelope . Nuclear Sap (Karyolymph). Nucleolus. Chromatin Materials: which are of two types:

-16-

Euchro matin. b) Heteroc hromat in. a)

1 - The Nuclear Membrane It is a basophilic membrane which surroun ds the nucleus and

disappears during cell division. With light microscope: it appears as a single line. With E/M: It is formed of 2 thin membranes separated by a perinuclear space:a) The Inner Nuclear Membrane has chroma tin granules on its inner aspect. b) The Outer Nuclear Membrane: It is rough because it has many ribosomes on its outer surface. Nuclear Pores: The nuclear membrane contains many nuclear pores which are covered by diaphragms. These diaphragms regulate the passage of RNA from inside to outside the nucleus.

2 - The Nuclear Sap It is a colloidal clear solution which is formed of nucleoproteins,

enzymes, DNA, RNA, lipids, phosphorus, potassium and calcium. By E/M it is known as interchromatin substance. According to the amount of nuclear sap in the nucleus we have two types of nuclei: 1. The open face nucleus in which there is a large amount of nuclear sap as the nucleus of liver cell. 2. The condensed nucleus which contains less amount of nuclear sap. but it has a very condensed chromatin network as in case of the nucleus of lymphocyte. Functions Of Nuclear Sap: It provides a medium in which ribonucleic acids (ribosomal, transfer and messenger RNA) move towards the nuclear pores.

-17-

3 - The Nucleolus The nucleolus is a rounded structure, basophilic in staining, rich in RNA and it is surrounded by chromatin material. The nucleolus disappears during cell division but it reappears in the new daughter cells. The nucleolus may enlarge in size in cells that are actively synthetizing proteins, and in rapidly growing malignant cells. It is formed of protein, RNA and DNA, certain enzymes as acid phosphatase and RNA methylase. Structure: By LIM, it appears as dark basophilic mass By E/M; it shows light area rich in nuclear sap and dark area called nucleolonema rich in granules and fibrils of DNA and RNA.

4- The Chromatin Material Definition: They are the basophilic particles and threads which form the chromosomes during the first stage of cell division. Structure: It is formed of nucleoproteins which are DNA bound to basic proteins called Histones. Staining: They are basophilic in staining due to presence of DNA. With The Light Microscope: appear as cmuse and fine basophilic granules. With The Electron Microscope: They are present as: X. :Peripheral Chromatin: Which lies close to the inner side of the nuclear membrane. 2. Chromatin Islands: Scattared as chromatin clumps between the nuclear membrane and the nucleolus. 3. Nucleolus Associated Chromatin: Which represents the condensed . chromatin material around the nucleolus. Types Of Chromatin: Two types are distinguished by the light and electron microscope

-18-

1. Euchromatin or Extended Chromatin or Active Chromatin:They are not visible by the light microscope. They represent the extended (uncoiled) parts of the chromatin. They stain very lightly with the basic stains. They are the most active parts of the chromatin threads. They control the process of protein synthesis. 2. Heterochromatin or Condensed Chromatin or the Inactive Chromatin: -

They are visible by the light microscope as coarse granules. They appear as masses of nucleoprotein called nucleosomes. They stain dark with the basic stains. The genes present in the condensed chromatin are inactive. They do not direct any protein synthesis.

Functions Of Chromatin:-

!. It directs and guides the process of protein synthesis inside the cell. 2. It stores the genetic informations of the individuals. 3. From th,e DNA of the chromatin material; the messenger, the ribosomal and the transfer ribonucleic acids are synthesized.

Nucleic Acids They are the bases of life, they control the cellular functions. They are of 2 Types: DNA and RNA

1- Deoxy-Ribonucleic Acid = DNA DNA represents the essential hereditary substance which constitutes the genes. Each DNA molecule consists of 2 molecular chains bound together in the form of a double helix. Each chain (helix) is formed of alternating phosphate and sugar (deoxyribose) groups. The 2 chains of DNA molecule are linked transversely by means of nitrogenous bases which extend laterally from each sugar group.

-19-

-

There are 4 types of Ditrogenous bases in DNA molecule which are:Adenine, Thymi ne, GuaDine and Cytosine.

RNA ... 2 - Ribonucleic Acid =

In general RNA is similar in its structu re to DNA, but with the following differences.!. DNA is presen t mainly in the nucleus, while RNA is present in the nucleus and cytoplasm. However, DNA is also present in the 2. 3. 4.

S.

mitoch ondria of the cytoplasm. With Methyi-Green-Pyronin Stain, DNA takes a blue colour, while RNA takes a red colour . Each RNA molecule is formed of a single strand of helix. However, some of the regions of RNA may contai n double helix. Each RNA strand cmitains ribose sugar instead of the deoxyribose found in DNA. RNA molecule contains the four differe nt nitrogenous bases found in D~A. Except that Thymi ne is replaced by anothe r nitroge nous base called Uracil (U). These are the 3 types of RNA

1. Ribo•o mal RNA· = r RNA = Ribosomes which serve as factories . for protein synthesis. 2. Messenger RNA = m RNA which carry the informatiQn codes which cpntro l protein synthesis. 3. Transf er RNA = t RNA which transfe r the specific amino acids to the ribosomes. N.B. The cell cycle is the changes which occur in the cell during its division (mitosis) and du~ng its rest (interphase). · Functi ons of the Nucleus It contro ls all the functions of the cell. It is a store house for gene.tic inform ations. The nucleus is an essential part of the cell which characterizes its type and its functions. It is the active centre for the format ion of the different types of RNA. -20 -

Genetics Cytogenetics is the study of heredity at the cellular level through cytological techniques and chromosomal preparations. Division of cells and union of gametes govern the continuation of species

Cell Division Types Of Cell Division 1. Mitotic CeO Division occurs in all cells of the body (somatic cells) except the germ cells of testes and ovaries. 2. Meiotic CeO Division occurs in the germ cells of testes and ovaries. 3. Amitotic Cell Division occurs in lower animals like amoeba, also in certain cells of the embryo and placenta.

Mitotic Cell Division It occurs in the somatic cells of the body. It gives two daughter cells, each contains a full number of

chromosomes. Cytoplasmic and Nuclear changes occur during mitotic cell division. The cytoplasmic changes: The centerioles form a spindle shape. The Nuclear Changes: the chromatin granules of the nucleus change into 46 chromosomes. The Following Are The Four Phases Of Mitosis: 1. Prophase Stage in which these changes occur: Migration of centrioles towards the poles of the dividing cell. Disappearance of the nuclear membrane and E p h nucleolus. . ar1y . rop ase The formed chromosomes become shorter and thicker. Each chromosome splits longitudinally into 2 chromatid~

-21-

2. Metapha se Stage in which the following changes occur: The chromos omes are arranged in the equatoria l plane. Each chromos ome is formed Early and Late Metaph ase of 2 chromat ids connected by the centrome re. Kinetochores are rounded bodies present at the centro meres, they form chromos omal microtu buies. Co.mplete formatio n of the mitotic spindle which is formed of: a) Cytoplasmic microtubules formed by the centrioles from the cytoplasmic protein by the MTOC organizing centre. b) Chromo somal micro tubules formed by the kinetochores of the chromos omes. 3. Anaphas e Stage in which: The Chromos omes split longitudinaly giving rise to 92 chromati ds 4. Telophase Stage in which the following changes occur:

Anapha se

The cleavage furrow is formed to divide the cell into 2 halves. of Formati on nuclear membrane, nuclear sap and nucleolu s in the daughter cells

Early and Late Telopha se

Two Daught er Cells

-22-

Meiotic Cell Division It occurs in the germ cells of testes and ovari_es.

Each mother cell gives rise to 4 daughter cells. Meiosis consists of 2 successive nuclear divisions (First and Second Meiotic Cell Divisions). The First Meiotic Cell Division. It involves the separation of the 2 homologus chromosomes giving rise to 2 nuclei, each contains 23 chromosomes. It occurs through 4 stages : Prophase, Metaphase, Anaphase and Telophase.

Crossing over of chromosomes may occur during the prophase stage of this division. The Second Meiotic Cell Division It comprises the 4 stages of mitosis; Prophase, Metaphase, Anaphase and Telophase. In Metaphase The 23 chromosomes are arranged in the centre. In Anaphase, each chromosome of the 23 split into 2 chromatids. The 23 chromatids duplicate to give 23 ·chromosomes.

Differences Between Mitosis And Meiosis 1. Mitosis gives l daughter cells, meiosis gives 4 cells. 2. Mitosis gives cells with full number of chromosomes (46), while meiosis give cells with half number of chromosomes (23). 3. Crossing over occur in Meiosis andnot in Mitosis. Certain Abnormalities May Occur During Cell Division As: 1. Nondisjunction (non-separation) Of Chromosomes or Chromatids. This will give rise to gametes with abnormal number of · chromosomes. 2. Misdivision Of Centromere. This will give rise to non-identical chromati ds which give abnormal chromoso mes called lsochromosomes.

-13-

Human Chromosomes A human-being is formed of billions of cells; these cells are of two types: a) Somatic cells which are present in the whole tissues of t~e body. b) Gametes which are the sperms and ova. Each somatic cell nucleus contains 46 chromosomes which are as follows:1. 22 pairs of identical chromosomes known as autosomes. -2. One pair of sex chromosomes which differ in the two sexes:In female somatic cells, the pair of sex chromosomes are identical and are called XX chromosomes. In male somatic cells, the pair of sex chromosomes are quite different, one being long and is known as X chromosome and the other is much smaller and is known as Y chromosome. Each gamete contains 23 chromosomes; the sex c~omosomes in the mature ovum are alike X, while the sex chromos9mes in sperms are unlike, so that we have 2 types of sperms some with X and others withY.

Karyotyping

Karyotyping is the study of the number, type and arrangement of chromosomes in the individuals. There are two categories for chromosomal studies: 1. A technique used to stuay the complete chromosome complement of an individual. 2. A technique used to study the sex chromosomes only of an individual The white blood cells are the most convenient cells for chromosomal studies. · The · leucocytes are incubated in media containing phytohaemagglutinin for 4 days to induce cell division. The cell division is then inhibited at the metaphase stage by addition of colchicine substance The chromosomes of the dividing leucocytes are fixed, stained, examined, photographed and then matched into pairs.

--24-

The Struchue Of A Human Chromosome Each chromosome is formed of two threads known as chromatids which are connected together at one point known as centromere. Each chromatid is formed of a number of subdivisions which form the Banding Pattern of chromatids. The bands are Banding Pattern identical on each homologous Of Chromosomes chromosomes. Each band is characterized by the presence of a specific type of protein. Q, G and C Bands are rich in adenine and .thymine.

Types Of

Chromo~omP.~

There are four otypes of chromosomes according to the position of their centromeres: 1. Metacentric chromosome: in which the centromere is median in position. 2. Submetacentric Chromosome: in which the centromere is present midway between the centre of the chromatids and their upper ends . 3. Acrocentric Chromosome: in which the centromere is present more near to the terminal ends of the chromatids.

+ - - - - Centromere

.,..Metacentric

+- Submetacentric

-

Acrocentric

-------- Tolecentric

-25 -

4. Telocentric Chromosome: Its centromere is present at the terminal ends of chromatids. The chromosomes can be arranged into 22 identical pairs according to the length of their arms and to the position of their centromeres. In karyotyping, the individual22 pairs of human chromo somes are numbered serially from 1 to 22 and then grouped into 7 groups: A, B, C, D, E, F, and G. + Sex chromosomes.

The Clinical Importance Of Chromosomal Studies 1. Chromosomal studies and chromosomal map help in clinical diagnosis of certain diseases and syndromes as:- Down's syndrome, Turner's syndrome and Klienfelter's syndrome. 2. Diagnosis of primary amenorrhoea, abortions and infertility 3. Diagnosis of malignant disease as myeloid leukaemia. 4. Prenatal diagnosis of diseases of the foetus.

Chromosomal Aberrations (Abnormalities) (Variations In Chromosomal Number And Structure) Both abnormalities may be restricted to autosomal chromosomes or restricted to the sex chromosomes.

Causes Of Chromosomal Aberrations 1. 2. 3. 4. 5.

Infections with German measles. Radiation; causes some chromosomal damage. Auto-immune diseases are correlated with chromosomal disorders. Pregnancy in old women. Presence of chromosomal imbalance in the parents.

1 - Aberrations In Chromosomal Number This occurs as a result of nonseparation of homologous chromosomes during cell division, it gives then trisomy or monosomy.

-26-

ome to one of the Trisomy in which there is an addition of a chromos drome= Mongolism, pairs of chromosomes, for example in Down's Syn 21. there is 3 chromosomes in number 21 = Trisomy The Mongol infant is characterized by with sloping eye~ Mentally retarded infant with characteristic face Small oral cavity. and protruded tongue. . - Broad nose, broa d hands and shor t broad neck s. Small genital organs and cardiac abnormalitie Generalized muscular hypotonia in early life.

2- Aberrations In Chromosomal Structure

are: Abnormalities in the structure of cnromosomes the chromosomes. l. Deletions or deficiencies of a piece or more from an extra piece of 2. Duplications of chromo~omes, or addition of chromosome to another chromosome. s are arranged in 3. Inversion of one chromosome in which the gene a reverse manner on the chromosome. s of chromosomes 4. Translocations or reattachment of broken piece to othe r chromosomes. lt of misdivision of 5. Form atio n of isochromosomes occurs as a resu mosomes. the centromere which gives rise to unequal chro

The Sex Chromosomes fertilization. Usually the sex of the embryo is determined just after can give similar The sex chromosomes in females are alike XX. They ova, each ovum with only one X chormosome. hey can give rise The sex chromosomes in males are unlike (X Y),t to two types of sperms; · others carry Y some of the sperms carry X chromosome and the chromosome. zoa with an X Nowadays they can differentiate between spermato or with an Y chromosome.

-1 7-

The Barr Body is a darkly-stained mass inside the nuclear membrane of about 600Jo of female cells only. It is called Female Sex Chro mati n. It also appears as drum stick-like mass attached to the nucleus of 60% of female blood leucocytes Fema le Sex Chro matin Significance Of Staining Of The Sex Chromosome Or Barr Body: 1. Diagnosis of sex in doub tful cases of hermaphr odism. 2. Studying the abnormalities of the sex chromos ome. 3. Diagnosis of abno rmal sexual development and matu ratio n. 4. Diagnosis of infertility, primary amenorrhea and abortions. 5. Identification of the foetal sex (male or female). Certain diseases may result if nonseparation of chro mosomes occurs in the sex chromosomes during the first meiotic cell division as: Kleinfelter's Syndrome: A male infant with mental retardation. The number of his chromosomes is 47 chromosomes and the sex chromosomes are XXY (Trisomy). Turn er's Synd rom e: A female infa nt with 45 chromosomes (Monosomy). She has only one X instead of XX. She has non-developed ovaries, breasts, external genitalia associated with prim ary amenorrhea.

Modes Of Inheritance The hum an zygote contains 23 pairs of chromosome s which are:22 pairs of Autosomal chromosomes. One pair of sex chromosomes. . Thus, there are two main modes of inheritance depe nding upon which chromosome is carrying the inherited character s or disease. 1. Autosomal Inheritance: when the inherited char acters or diseases are carried by genes present on the autosomal chromos omes. The inherited disease or character may be dominant or recessive. Madness is an example of a dominant inherited disea se. Brown Eyes is an example of a dominant autosom al inherited character. -2 8-

AlbialsiD is an example of a recessive autosomal inherited disease. Tbe albino Individual has a rosy-coloured skin, white hair an~ red eyes. 2. Sex-Dnked Inheritance: In this case the inherited diseases or characters are carried by genes present on one of the sex-chromosomes either on the X or Y chromosomes Examples of X-c~romosome inheritance diseases are Haemophilia and Colour Blindness. Example ofY- chromosome inheritance disease is the 'Hairy- Ears' in male individuals.

Blood Groups The A,B, AB & 0 Blood Group System The blood group of any individual belongs to one of the four major blood groups which are A,B, AB and 0. Now there are 6 phenotypes for blood groups which are: Al, A2, B, A 1B, A2B and 0 -

The locus (place) of the genes for the A,B, AB&O blood groups is preserit on the chromosome number 9.

Group A Individuals They have antigen A on their red blood corpuscles and anti B antibodies in their serum (Antigen A + Antibody b). - The major phenotype of group A is A. - There are two subtypes for group A individuals which are the following:1. Subtype At individuals. (Their blood groups are AI). 2. Subtype Al individuals. (Their blood groups are A2).

·-

-29....;...

Group B Individuals -

They have antigen B on their red blood corpuscles and Anti A antibodies in their serum (Antigen B + Antibody a).

Group AB Individuals They have antigen A B on their red blood corpuscles but no antibodies in their serum (Antigen AB + No antibodies). There are l subtypes of group AB which are: 1. Subtype A1 B individuals. l. Subtype A2 B ·iadvlduals.

Group 0 Individuals They have no antigens on their red blood corpuscles, while their serum contains anti A and anti B antibodies (No antigens + Antibodies a and b).

Medical Importance Of Blood Groups Blood groups are very important for blood transfusion and for medicolegal applications. The donor's blood must be free from diseases such as: AIDS, Syphilis, Malaria and Infective hepatitis.

The Rhesus Factor (Rh Factor) The Rhesus factor i$ an antigen found on the red blood corpuscles -

of about 850fo of the individuals. Persons whose blood contains the Rh antigen are called Rh positive. Persons whose blood is free from this Rh ~ntigen are called Rh negative individuals. An Rh -negati ve woman may form anti Rh bodies in her plasma when she gets pregnant with an Rh + positive foetus.

-30-

Blood ma, (550Jo) and Blood Blood is a viscous fluid, formed of: Blood Plas Cells (450Jo). substances, inorganic Blood Plasma is formed of: Water, organic . substances, gases, hormones and enzymes ber In Human Body:Types of Bloo~ Cells And Their Average Num s: abo ut 4.5 to 5.5 millions 1. Red Blood Corpuscles or Erythrocyte per cubic millimetre. ut 4000 to 11000 per cubic 2. White Blood Cells or Leucocytes: abo miJJimetre. ut 200,000 to 400,000 per 3. Blood Platelets or Thromboeytes: abo cubic millimetre. The Ma jor Functions Of Blood Are :and hormones to tissues. 1. Transport of oxygen, nutritive substances products through the lungs, 2. Removal of carbon dioxide and waste kidneys and sweat glands. 3. Control of bod y temperature. 4. Maintenance of acid-base balance. ns. 5. Protection of the body against infectio

Red Blood Corpuscles per cubic millimetre. Number: In males: From 5 to 5.5 millions ic millimetre. In females: From 4.5 to 5 millions per cub The number is less in females due to: ress blood development. (1) Th.e secreted female hormones dep of blood every month. (2) Menstruation in females causes loss s or in haemoglobin Anaemia: Decrease in number of RBC percentage. Causes and Types of Anaemia:. , copper, and vitamin Bll . 1. Deficiency Anaemia, deficiency of iron -~i

-···

2. Haemorrbagic Anaemia, as haemorhage from nose , gums, and piles. 3. Haemolytic Ana emia : in excessive destruction of RBCs. 4. Aplastic Anaemia: in diseases of bone marr ow. Polycythaemia or increase in the num ber of RBCs: It occurs in low oxygen tension, in heart and lung diseases. Sha pe Of RBCs They are rounded, non-nucleated biconcave discs. They show a rouleaux appe aran ce in bloo d streams. Abn orma l Shapes of RBC s: In cert ain anae mias RBC s may be pear-shaped (poikilocytes) or may be biconvex (spherocytes) or may be oval in shape (ovalocytes). Size of RBC s:No rmal diameter is 7.5 microns and the norm al thickness is 1.9 microns at the periphery and 1.1 microns at the centre of RBCs. Red Bloo d Cor pusc les And Blo od Plat e lets Abnormalities in The Diam eter Of RBCs: 1. In Macrocytic Anaemias there is an increase in the diameter. 2. In Microcytic Anaemias there is a decrease in the diameter of RBCs. 3. In Cases Of Anisocytosis, different diameters of RBCs are present. Price Jone s Curve shows the relation between the num ber of RBCs and their diameters. Colo ur OF RBCs: - RBCs are greenish yeUow in colour due to presence of Haemoglobin. Abn orma l Colo ur of RBCs: a) RBCs with less HbOJo are called hypochromic. b) RBCs with more Hb% than norm al are called hyperchromic. c) In t~get cell anae mia, the Hb is concentrated in the centres.

-3 2-

Chancteristics Of RBCs: They are not true cells, they have neither nuclei nor organoids. They are surrounded by cell membranes which are plastic. The R.B.Cs are filled with haemoglobin (Hb). Haemolysis: Rupture of the cell membrane and loss of Hb outside the R.B.Cs is called haemolysis .. The Normal Osmotic Pressure: of R)JCs is 0.90Jo saline Life Span Of RBCs: They can live for about 4 months.

Adaptation Of The Structure Of R.B.Cs In Order To Perform Their Functions 1. The cell membrane of RBCs is Plastic. It allows RBCs to change their shape. RBCs can be squeezed inside narrow capillaries. 2. The biconcave surfaces of RBCs increase their surface area, through these surfaces gaseous exchange takes place. 3. The cell. membrane of RBCs is formed of lipoprotein, it is highly selective, it allows easy exchange of carbon dioxide and oxygen through· it. 4. There is neither nuclei nor cell organoids in RBCs, this prevents RBCs from reproduction. Their abse;J.ce also allows free space for haemoglobin. S. The main function of RBCs is to enclose haemoglobin, this haemoglobin combines easily with oxygen to form oxyhaemoglobin which goes to the tissues to supply them with oxygen. 6. RBCs are rich in carbonic anhyd nse enzyme which facilitates combination of carbon dioxide with haemoglobin .. The Red Blood Count: Red blood carpuscles are counted by the haemocytometer which is formed of a diluting pipette and a counting slide. We dilute the obtained blood by saline (0.90Jo).

-33 -

Leucocytes They are also called White Blood Cells. General Characteristics of Leucocytes: -

They are colourless, but when packed together, appear white. They are true nucleated cells. They contain all the cell organoids and the cell inclusions . They have an amoeboid movement, so they can penetrate through the capillary walls and perform their phagocytic function in the C.T. They contain no haemoglobin. Types Of Leucocytes: There are S types of leucocytes : Neut rophil, Eosinophil, Basophil, Lymphocyte and Monocyte. Total Number Of Leucocytes: They vary in number from 4000 to 11.000 per cubic millimetre. At birth the total leucocytic count is about 16.000 per cubic millimetre. Leucocytosis: It is the increase in number of leucocytes above 12.000 per cubic millimetre. Causes Of Leucocytosis: 1.. Physiological leucocytosis: Occurs in pregnancy, and in newly born infants. 2. Pathological Leucocyto~s: Occurs in acute and chron ic diseases. Leucopenia: Is the decrease in number of leucocytes below 4,000 per cubic mm. This may occur in: typhoid fever, influenza and after exposure to X-ray or after taking certain antibiotics.

-34 -

Counting Of Blood Leucocytes Tbere Are 2 Types Of Leucocytic Count: A) Total Leucocytic Count: It is the determination of the total number of leucocytes per cubic millimetre. It is done by the haemocytometer which is formed of: a diluting pipette and a counting slide. - The diluting fl~id for total leucocytic count is forJDed of: equal volumes of: 2'1o Acetic acid (to cause haemolysis of R.B.Cs) and lt2'1o Geatian violet (to stain the nuclei of leucocytes).

B) Differential Leucocytic

Count

It is the determination of the per~ntage of each type of leucocytes in the blood~

1. It is done by making a blood film and staining it with Leishman. 2. We count the number of each type of leucocytes in different fields of a blood film. 3. We record the number of each type in a table-form. 4. We find out the percentage of each type of leucocytes in relation to the total number counted in this blood film. Siinlflcance of Usina the Differential Leucocytic. Count By means of the differential leucocytic count we can diagnose certain diseases for examples: -

Increase in the percentage of neutrophils, indicates presense of acute infections. Increase in the 'lo of eosinophils and basophils, indicates presence of parasitic or allergic diseases. Increase in the 'lo of lymphocytes and monocytes, indicates presence of chronic infections as T.B. and syphilis.

-35-

Differences Between RBCs And Leucocytes RBCs I.

2. 3. 4. 6.

7. 8. 9.

10.

11. 12. 13. 14.

Leucocytes

Average number: from 4.5 to 5.5 millions per cubic millimetre. They are of one type. They are corpuscles = not true cells. They have no nuclei and no cell organolds. They are biconcave corpuscles. They appear in rouleaux. Colour : greenish yellow. Diameter 7.5 microns. They are easily haemolysed. They contain haemoglobin. They carry oxygen and C02 while they are inside the B.V; They develop in the red bone marrow. Life span about 4 months.

(.

2.

3. 4. 6.

7. 8. 9.

10. ll.

12.

13. 14.

Number: from 4000 to I 1.000 per cubic millimetre. They are 5 types. They are true cells. They contain nuclei and cell organoids. They have an amoeboid movement. No rouleaux appearance. They are colourless. Diameter from 8 to 18 microns. They resist haemolysis partially They have no haemoglobin. They are phagocytic cells but outside the B.V. They develop in red bone marrow and in the lymphatic tissues. Life span from few days to years.

Types Of Leucocytes There are 5 types of leucocytes which are classified into granula r leucocytes (neutrophil, eosinophil and basophil) and non-granular leucocytes (lymphocyte and monocyte).

-36-

Granu lar Leucocytes These are the Neutrophils, the Eosinophils and the Basophils.

Neutrophils Or Polymorphonuclear Leucocytes (60- 700Jo) Their percentage varies from 60 to 700Jo of the total leucocytes. Their diameter varies from 10 to 12 microns. Neutr ophils The nucleus is single but segmented, it is formed of 2 to 5 segments connected with each other by chromatin threads. Neutrophils have an amoeboid movement, they can protrude pseudopodia in order to engulf microorganisms. The cytoplasm of neutrophils contains few mitochondria, endoplasmic reticulum, glycogen granules and the following Two Types 6f Granules: 1. Azurophllllc Granules: which are few in numbe r and large in size. They are considered as lysosomes because they are very rich in hydrolytic enzymes. 2. Specific Granules.: which are numerous and small in size. They contain collagenase and alkaline phosphatase enzymes. They contain also lactoferin which is a bacteriostatic substance.

Functions Of N eutrophlls 1. 2. 3. 4. 5.

They are phagocytic to micro-organisms. They secrete proteolytic enzymes. They secrete trephone substances which help in healing of wounds. Neutrophils help other leucocytes to migrate to the inflamed areas. They stimulate bone marrow to develop more leucocytes.

Life span of neutropbils is 4 days. They may change to pus cells.

-37 -

Neutrophilia = increased number of neutrophils. This occurs in acute infections which may produce pus as in: tonsillitis, appendicitis and in any abscess formation. Neutropenia or Neutrophil Leucopenia: It is the decrease in the number of neutrophils. It occurs in typhoid fever, T .B., influenza and in severe poisoning. Ameth count: He classified neutrophils into S classes according to the number of segments in their nuclei. Schilling Count: He classified neutrophils into mature neutrophils with segmented nuclei and immature neutrophils with non-segmented nuclei (stab and juvenile types).

2. Eosinophil Leucocytes: 1-40Jo Their percentage: varies from 1 to 40Jo of the total leucocytes. Their diameter: varies from 10-15 microns. The nucleus is bilobed and is called horse shoe- shaped nucleus.

Eosinophi l

By the electron microscope, the cytoplasm contains few mitochondria, small Golgi body and few endoplasmic reticulum. It is rich in coarse shiny acidophilic granules. These granules are considered as Lysosomes. Eosinophils contain the following enzymes: 1. Histaminase enzyme to destroy histamine substance. 2. Sulphatase enzyme to destroy sulphate substances

Functions of Eosinopbils: 1. They are attracted to the site of allergic reactions by eosinophil chemotactic factors which are released by mast and basophil cells.

-38-

mes to destroy 2. Eosinophils contain histaminase and sulphatase enzy histamine and sulphated substances. ody complex in 3. Eosinophils can phagocytose the anti gen - antib allergic conditions. Life span of eosinophil is from 8 to 12 days. ophils which Eosinophilia = increase in the percentage of eosin occurs in: asth ma, skin 1. Allergic diseases as urticaria, eczema, bronchial and blood diseases. lostoma. 2 . Parasitic diseases as ascaris, bilharzia and anky which occurs Eosinopenia : = decrease in number of eosinophils during treatment with cortisone.

3. Basophil Leucocytes: 1/2 to 1 OJo Their percentage varies from 1I 2 to 1OJo. Their diameter varies from 10-12 microns. ron - dense Their cytoplasm is filled with large basophilic elect granules similar to those of mast cells. These granules can be stained by Giemsa stain. Their nuclei are large and irregular in shape. Their functions are related to production and carriage of histamine and heparin. They are slightly phagocytic cells. Bas oph il Life span from 10-15 days. phils. This Basophilia = An increase in the percentage of baso basop billa occurs in : diseases. liver cirrhosis, small pox and in allergic and parasitic

-3 9-

Non Granular Leucocytes 1. Lymphocytes: l0-300Jo

-

Their percentage varies from 20- 300Jo of the total number of blood leucocytes. According to the diameter, lymphocytes are classified into: Small and Large.

1. Small Lymphocytes: Their percentage in the blood is about 1S-200Jo. Each lymphocyte is about 6-8 microns in diameter. The cytoplasm of small lymphocytes is scanty and it contains few azurophil granules and many free ribosomes. The nuclei are smaU, darkly stained and ftiUng the whole cytoplasm.

There are two types of small lymphocytes: a) T-Lymphocytes (7S'lo). b) B-Lymphocytes (2S'lo). Small T and B Lymphocytes are covered by microvilli. Their cytoplasm shows many free ribosomes, few mitochondria~ few endoplasmic reticulum and a pair of centrioles. l. Large Lymphocytes: -

Their percentage in the blood is about S to lOOJo. Each lymphocyte is about 10 to IS microns in diameter. The cytoplasm of large lymphocytes is abundant and it contains many ribosomes, mitochondria and a well-developed Golgi apparatus. The nucleus is slightly indented and appears pale after staining.

Lymphocytosis:Increase in the percentage of s~all and large lymphocytes above 300Jo is called lymphocytosis.

-40~

Causes of Lymphocytosis: Lymphocytosis occurs in chronic diseases as in: Whooping cough, ·T.B., Syphilis and in Glandular fever.

Classifications Of Small Lymphocytes According to the Origin and Functions, Small Lymphocytes Are Classified into: T-Lymphocytes and B-Lymphocytes:

T -Lymphocytes: 750Jo -

-

They are termed as T-Lymphocytes because they are Thymus dependent lymphocytes. They require the presence of the thymus gland for their development and for their maturation. They constitute about 750Jo of the circulating lymyhocytes. They have a long life span, they can live for years. T-Lymphocytes originate from mother cells called colony forming cells which are present originally in the bone marrow.

These mother cells migrate from the bone marrow to the thymus gland. They proliferate in the thymus to be changed into T-lymphoblasts and then to T-lymphocytes. o

Types And Functions Of T -Lymphocytes 1. T-Helper Cells which help B-lymphocytes to perform their immune

functions. 2. T.Suppressor Cells which suppress the functions of B-and T-lymphocytes. 3. T-Cytotoxic Cells: They release cytotoxic elements which cause lysis to viral infected cells, tumour cells and certain bacteria (This function is called Cellular Immunity). 4. T-Lymphokines Producing Cells: These lymphokines have the following functions: · a) They attract macrophage cells to migrate to the sites of infections.

-41-

b) They stimulate proliferation of bone marrow cells. c) They inhibit viral replication throu gh the action of their interferons. d) They can kill certain bacteria as T .B. through the actio n of their ly mphotoxins. 5. T-Memory Cells which can defend the body against the same antigen if it enters the body again.

B - Lymphocytes: 250Jo They are termed as B-lymphocytes because they are Bursa dependent lymphocytes in birds, they develop in the bursa of Fabricius in birds. They are derived from the primitive stem cells of the bone marrow. They cons titut e 25 OJo of the circulating blood lymphocytes. 25%). Their life span is about 3 months. Lym phoc ytes

Functions Of B-Lymphocytes

1. B-Lymphocytes are responsible for the development of humoral immunity, they are transformed into plasma cells which secrete many antibodies in the form of gamma globulins which circulate in the blood stream (hence the name humoral immunity) . 2. B-Lymphocytes act as B-Memory Cells: The mem ory cells can produce secondary immune response when they are expo sed once again to the same type of antigen.

-42 -

2. Monocytes: 3 to 80Jo Their percentage varies from 3 to 8%. their diameter varies from 14 to 18 microns. Their cytoplasm is non -granular and is not clear. It is rich in azurophil granules which Monocyte are the lysosome bodies. The cytoplasm is rich in: acid phosphatase and other enzymes. MonocytesmovetoC.T. during infections. Nucleus: The nucleus of monocytes is pale, large and slightly indented. It may be kidney shaped. Its chromatin is less condensed than that of a lymphocyte. Functions Of Monocytes: In inflammation monocytes migrate from the blood to connective tissue, ~ey change into Macrophage cells or Histiocytes. Monocites can phagocytose micro-organisms and dead blood cells. Monocytes can fuse with other monocytes to form Giant Phagocytic cells and Bone Osteoclasts. Life Span: It is about 3 days in the blood stream. Monocytosis = increase in tbe number of monocytes in the blood. This Occurs In Chronic infections as: Malaria, Typhus, T .B., Syphilis and Glandular Fever.

Blood Platelets Shape: platelets are not cells, they are small oval or rounded non-nucleated bodies, similar to plates, and are found in mammals. Number of blood platelets varies from 200,000 to ~,000 per cubic millimetre. The average number = 1I 4 million per cubic millimetre. Diameter: 2 - 4 microns and they have no nuclei.

-43-

Structure Of Blood Platelets With the Ught microscope, each blood platelet is oval or rounded in shape formed of a peripheral pale clear part called Hyalomere, and a central granular basophilic part called Chromomere. With the electron microscope, the cell membrane is irregular. The Hyalomere contains bundles of microtubules and microfilamen ts. The Chromomere contains: Alpha graaules which are lysosomes. Mitochondria or Beta granules. Sydersomes or Delta granules. Dense Graaules rich in serotonin A TP, AD P and Ca. Glycogen granules which are present in small or large groups. -

Life Span of Blood Platelets is from 5 to 10 days.

Function Of Blood Platelets I. Blood Agglutination: They form a white thrombus. l. Blood Coagulation: platelets and RBCs form a red thrombus. 3. Blood platelets release serotonin substance which is a vasoconstrictor. 4. Blood platelets cause clot retraction. In Purpura the bleeding time is prolonged due to diminished blood platelets.

Blood Platelet Count I. By the use of the haemocytometer, we dilute the drop of blood 100 times by Rees and Ecker fluid which prevent clotting and adhesion, it also stains the blood platelets. 2. By the use of new electronic counting apparatus.

-44-

Haemopoiesis (Formation Of Blood Cells) Different blood cells are developed in. 1. Myeloid Tissue (Bone Marrow). 2. Lymphatic Tissue (Lymph nodes, spleen, tonsils and thymus).

Bone marrow (Myeloid Tissue) There are Two types of bone marrow : 1. Red Active Bone Marrow present in the bone of the foetus and

children up to 7 years old. In adults, it is present mainly in the centre of flat bones. 2. Yellow Inactive Bone Marrow present in the shafts of adult long bones.

Structure Of Myeloid Tissue (Red Bone Marrow) It is formed of:-

1. Stroma of the following Developing Blood Cells fixed cells: a) Reticular branched cells. b) Fat cells which are the largest cells in the bone marrow. c) Endothelial cells lining blood capillaries, arterioles and sinusoids. d) Perivascular mesenchymal Pericyte cells.

2. Blood Sinusoids which are fenestrated blood channels. 3. Free Mature and Immature Blood Cells. Functions Of Red Bone Marrow. 1. Production of blood cells.

-45-

2. Destruction of Red Blood Cells. 3. Storage of iron in bone marrow macrophages. Development of blood ceUs depends upon: l. The presence of stem cells called: Colony Forming Cells. 2. Growth Factors and Erythropoietin factor secreted by the kidny.

Erythropoiesis They are developed in the red bone marrow. Their development depends upon: 1. Presence of healthy colony forming cells in the bone marrow. 2. Erythropoietin hormone3. Iron, folic acid, vitamin B 12 and amino acids.

Proerythrobl ast

Basophil

The stages of maturation of an RBC Erythroblast t~kes about 7 days. The basic process is the synthesis of Polychromat ophil haemoglobin. Erythroblast During maturation of an erythrocyte, these changes occur: Normoblast Disappearance of the nucleoli of the developing cells. Decrease in the nuclear chromatin. l: Reticulocyte The nucleus will be extruded outside Mature R.B.C the cell. Disappearance of mitochondria. Development Of R.B.Cs Gradual decrease in the basophilia of the developing cells. Gradual increase in the acidophilia and haemoglobin.

-46-

Erythrocytes are developed through the foUowing stages: 1. Haematopoietie Stem CeUs. It is a branched cell with basophilic cytoplasm. · 2-3 Coloay Formiag CeUs They are rounded cells with rounded nuclei and basophilic cytoplasm.

4. Proerythroblast Rounded cell with basophilic cytoplasm and rounded nucleus. 5. BasophD Erythroblast Rounded cell with basophilic cytoplasm, its nucleus has no nucleoli.

6. Polychromatophil Erythroblast

.

Rounded cells with slight amount of haemoglobin. 7.

Noi'Dloblast Rounded cell with more, haemoglobin and pyknotic nucleus.

8.

Reti~oeyte

Ro~ded cell with more haemoglobin and a reticulum formed of the remnant of the polyribosomes. 9. Mature Erythrocytes: Non nucleated corpuscles filled with haemoglobin.

-47-

Stages Of Development Of Granular Leucocytes (Neutrophil, Eosinophil And Basophil) 1. Haematopoietic Stem Cells. 2-3 Colony Forming Cells For Granulocytes: Rounded cells with rounded nuclei. 4. Myeloblast: Large cell with basophilic non granular cytoplasm.

Myeloblasl

Promyelm:y le

5. Promyelocyte _Large cell with azurophilic non differentiated granules. 6. Myelocytes (Neutrophil, Eosinophil and Basophil) Differentiation of granules occur in these cells giving rise to neutrophilic, basophilic and eosinophilic myelocytes. 7. Metamyelocyte (Neutrophil Eosinophil and Basophil) They have more specific granules and curved rod shaped nuclei. 8. Mature Neutrophlls, Eosinophils and Basophils. They Contain specific granules and characteristic nuclei.

-48-

Myelocyle

Melamyeloc~· re

Juvenile Polymorph t•olymorph Neulrophil Developmenl Of Neulrophil

Development Of Non-Granular Leueoeytes Development Of Lymphocytes We have two types of lymphocytes: l. B- Lymphocytes 2- T- Lymphocytes Development Of B- Lymphocytes They are developed through the following stages: 1. Haematopoietie Stem CeUs. - They are small branched cells with small nuclei. - They give rise to Colony Forming Unit. 2. Colony Fonning Unit: - They are small rounded cells with small nuclei. They differentiate into B-lymphobasts. 3. B-Lymphoblasts: - They are small cells about 8-10 microns in diameter. - They are called transitional cells. - They differentiate into small B-lymphocytes. 4. B-Lymphoeytes: - They are small cells with deeply stained nuclei. - They leave the bone marrow to enter the blood circulation. They are then filtered in the spleen, lymph nodes, tonsils and in the intestinal lymphatic nodules. In these tissues they are activated by antigens to be changed into plasmablast cells and then into plasma cells which secrete antibodies. B-Lymphocytes are involved in humoral immunity. N .B. LeukeJD.ias are malignant diseases of leucocytes characterized by a release of large numbers of immature leucocytes in the blood.

-49-

Development Of T -Lymphocytes The T-lymphocytes develop through the following stages: 1. Haemat opoietic Stem Cells. They are branched embryonic cells with small nuclei. They are present in the embryonic blood islands of the bone marrow . They differentiate into: 2. Colony Formin g Unit (CFU): They are small rounded cells with rounded nuclei. In the foetus and the new born infants, these cells migrate to the cortex of the thymus gland where they are affected by the thymic hormones. They then develop into T -lympho blasts. 3. T-Lymphoblasts: They are small immatu re rounded cells. They leave the thymus and are called post thymic cells, they then differe ntiate into T -lymphocytes. 4. T- Lymphocytes: - They are small rounded cells with rounde d nuclei circulating in the blood. These cells are involved in mediation of cellular immunity.

-50-

Lympho blast

Large · Lympho cyte

Small Lympho cyte Develop ment Of Lympho cyte

Development Of Monocytes Monocytes are developed through the following stages: 1. Haematopoietic Stem Cells. They are branched undifferentiated mesenchymal cells.

2. Colony Forming Unit (CFU): They are small rounded cells with small nuclei, they differentiate into: 3. Monoblasts or promonocytes They are large cells with large nuclei. They can differentiate into monocytes. 4. Monocytes: They are large cells with large indented nuclei. Sometimes they migrate to the tissues to be changed into phagocytic macrophage cells. Stem Cell

For Monoblast

Monoblast

Monocyte

Development Of Monocyte

-51-

Development Of Blood Platelets They are developed in the red bone marrow through the following stages: 1. Haematopoietic Stem Cells. 2. Colony Forming Unit (CFU): 3. Megakaryoblast: It is a large cell with a rounded indented nucleus which has two clear nucleoli. The cytoplasm is basophilic and is rich in ribosomes. 4. Promegakaryocyte: It is a larger cell with a large multilobed nucleus. Its cytoplasm is basophilic and contains fine azurophilic granules. The cell can differentiate into megakaryocyte 5. Megakaryocyte: It is a very large cell with a large multilobed nucleus (Mega = large, Megakaryocyte Karyo =nucleus and cyte = cell). It is about 40 microns in diameter. The cytoplasm is less basophilic and is rich in fine azurophil granules. The nucleus is single, but it is large, deeply stained and is formed of many lobules.

-52-

Tissues OF The Body The Basic Tis sues Of The Body Are 1. Epithelial Tissue. 2. Connective Tissue. 3. Muscular Tissue. 4. Nervous Tissue.

Epithelial Tissue Types Of Epithelial Tissue 1. Simple Epithelium (one layer of cells forming surface sheets). 2. Stratified Epithelium (many layers of cells above each other forming covering or lining sheets). 3. Glandular Epithelium (groups of epithelial cells whose functions are secretion). 4. Neuro Epithelium (groups of special type of cells whose functions are perception of special sensation).

I. Simple Epithelium Types Of Simple Epithelium 1. Simple $quam ous. 2. Simple ,Cubical (cuboidal). 3. Simple Colum nar. 4. Simple Colum nar Ciliated. 5. Pseudo-stratified Columnar. 6. Pseudo-stratified Columnar Ciliated.

1

Simp le Squa mou s Epithelium

Formed of a single layer of flat cells with flat nuclei.

Simple Squam ous

Sites Of Simple Squamous: 1. Endothelium of heart, blood vessels and lymph vessels.

2. Mesothelium of pleura, pericardium and peritoneum. 3. Certain cells in the lung alveoli, Bowm an's capsule and loop of Henle in the kidney. -53 -

2 - Simple Cuboidal Epithelium It is formed of a single layer of cube-like cells with central roun ded nuclei. Cuboidal cells are mainly responsible for secretion as in gland or absorption as in kidney.

Simp le Cubi cal

Sites Of Simple Cuboidal Epithelium s, pancreas 1. Secretory units as thyroid follicles, acini of salivary gland and sweat glands. 2. Convoluted tubules of kidney. 3. Small ducts of glands. 4. Covering the eye lens.

3 - Simple Colu mna r Epithelium It is formed of a single layer of tall

columnar cells with basal oval nuclei.

Types, Sites and Functions a) Secr etory Simp le Colu mnar Cells: Present in the stomach and cervical cana l of uterus. b) Absorptive Simple Colu mnar Cells: Present in intestine, convoluted and Simp le Colu mmu collecting tubules of kidney. The surfaces of absorptive cells are s from the covered with microvilli which are cytoplasmic projection cell membrane.

-54 '.

c) Goblet Cells. -Striated Border

They are modified columnar cells. They are cup-like cells with basal oval nuclei.

.....----:--__._G oblet Cell

Goblet cells are present in intestine, larynx, trachea, large bronchi and Eustachian tube. They secrete mucin and are · considered as unicellular glands.

· Simple

Columnar

4 - Simple Columnar Ciliated Epithelium It is formed of a single layer of columnar cells with basal oval nuclei. The surfaces of these cells are covered with cilia. Each cilium is formed of a shaft, basal body and a rootlet.

Sites Fallopian tube and uterus. The central canal of spinal cord is lined with simple cuboidal ciliated Bony part of Eustachian tube. Small bronchioles of lung.

. Stmple Columnar Ciliated

5 - Pseudo-stratified Columnar

·

It is formed of a single layer of columnar cells. The cells are crowded over each . other, but all of them rest on the basement membrane. Some cells do not reach the surface, therefore their nuclei are present at different levels forming false raws. Yseude-Strat ified Col11111nar

-55-

Sites -

Upper part of vas deferens. Large ducts of salivary glands. Upper part of male urethra

6 - Pseudo-st ratified Columnar Ciliated Epithelium It is formed of a single layer of columnar cells which are crowded over each other. The nuclei of these cells are present in false irregular raws. The surfaces of these cells are covered with cilia. Goblet cells are present between the columnar ciliated cells. The motile cilia contain microtubules and microfilaments. The non-motile cilia contain no contain but microt ubules microfilaments.

Pseudo-stratified Columnar Ciliated

Sites A - Pseuo-stratified Columnar Ciliated Epithelium With Goblet Cells and Motile Cilia Is Present In:Nose, nasal sinuses, nasopharynx, trachea and bronchi. Cartilagenous inner part of Eustachian tube. Lacrimal sac of eye. B- Pseudo stratified Columnar Epithelium but with Non-Motile Cilia Is Present In: Epididymis.

II. Stratified ·Epithelium It is formed of many layers of cells, it is classified ace or ding to the type of the most superficial cells, therefore we have the following Types Of Stratified Epithelium;-

-56-

. ·-

1. Stratified Squamous Epithelium (the superficial' cells are squamous). 2. Stratified columna r Epithelium (the superficial cells are columnar). 3. Stratified Columna r Clliated Epithelium (the superficial cells are columnar ciliated). 4. Transitional Epithelium (the superficial cells are broad cuboidal).

1 - Stratified Squamous Epithelium It is a thick type of stratified epithelium formed of many layers of cells one above the other. The number of layers ranges from 5 to 30 layers of cells. The cells rest on a clear wavy basement membrane. Under the basement membrane there is C.T. containing blood and lymph vessels. The basal ceUs are well nourished and are formed of columnar cells with oval basal nuclei, from these ,basal cells, the other layers germinate. Hemidesmosomes are present between these cells and the basement membra ne. The intermediate layers are polygonal cells (have many sides) with desmosomal junction between their cell boundaries (spiny appearance). The superficial layers of cells, are flat squamous cells which may be nucleated or not. They are not well-nourished and they are exposed to air, so they are gradually shed off. The surface may be covered with

Non -Keratini sing

Stratified Squamou s

-57-

fresh non-keratinizing squamous cells as in oesophagus. In other area as in the skin, the epithelium is covered with keratin layer which 1 · formed of the dead superficial cells forming keratinizing epithelium . Sites: St. Sq. Epith. has a protective function so it is present in the following dry areas: a) Skin (Epidermis of skin). b) Openings upon the skin: External ear, External nose, outer surface of the lip and anal orifice. Non-keratinizing stratified Squamous Epithelium is present in these wet surface areas: . a) Oral cavity, inner surface of the lip, tongue, gums and palatine tonsils. b) Oesophagus, Oroph arynx and vocal cords. c) Corne a and the exposed part of the conjunctiva. d) Vagina, terminal parts of male and female urethrae and a.nal canal.

2 - Stratified Colum nar Epithelium

It is simila r in structu re to stratified squam ous epithelium but: Its layers are less in number. The superf icial cells are non-keratinizing columnar cells.

1. 2. 3. 4.

It is present in the following areas : Fornicies of conjunctiva of the eye. Penile part of male urethra . Large ducts of glands. Recto-anal junctio n.

Stratified Columnar

3 - Stfatified Colum nar Ciliated It is similar in its structure to stratified squam ous epithelium but : It is formed of few layers of cells. The superficial cells are non-keratinizing columnar ciliated cells .

-58 -

This type of epithelium is present in: 1. Foetal Oesophagus.

2. Nasal surface of soft palate. 3. Laryngeal surface of epiglottis.

4 - Stratified Cuboidal Epithelium When the free surface of the stratified .epithelium is covered with cuboidal cells, it is called stratified cuboidal. The stratified cubical is present in the ducts of sweat glands, and in seminiferous tubules of the testes. The transitional epithelium can be considered as stratified cuboidal epithelium. Stratified Cubical

Transitional Epithelium It is a stratified type of epithelium which is present in the urinary tract. The epithelium rests on thin and corrugated basement membrane.

Its superficial cells are cuboidal in shape with convex outer surfaces and concave inner surfaces. Some of the superficial cells may contain two Transitional nuclei. The superficial cells are covered with a mucus-like substance, and a protecting membrane. This membrane acts as an osmotic barrier between urine and tissue fluids. It also protects the epithelium from the high acidity or high alkalinity of urine.

-59-

The basal ceO layer is formed of high cuboidal cells. The intermediate cells which are present between the basal and superficial layers are polyhydral cells and are separate4 from each other by mucus-like substance in their intercellular spaces. -

The presence of mucous substance between the cells facilitate gliding of cells on each other, so the transitional epithelium may be formed of 3 to 4layers only in full distended urinary bladder or 6 to I layers in an empty bladder. ·

-

The superficial cells may change temporarily into squamous cells when the bladder is full of urine.

N.B. Metaplasia means change of one type of epithelium into another type as in BUharziasls of bladder, its transitional epithelium changes into stratified squamous epithelium. The Tnnsltional epithelium Is present in these areas: 1. Minor and major calyces of the kidney. 2. Pelvis of the ureter, the ureter and the urinary bladder. 3. The prostatic part of male urethra and the inner part of female urethra. N .B. In order to study the sites of the different types of epithelium you should

Remember The Following Rules 1. The smooth endothelium which are in direct contact with blood as heart, B. V., lung alveoli and Bowman's capsule are lined with Simple Squamous Epithelium. 2. The Skin and its Openings and Oesophagus are lined with Stntified Squamous epithelium. 3. De Upper Resplntory Passages as Nose, Larynx, Trachea and Bronchi are lined with Pseudo Stntified Columnar CUiated Epithelium With Goblet CeUs and MotUe OUa.

-60-

4. The Urinary Passages as Calyces of Kidney, Pelvis of ureter, and urinary bladder are lined· with Transitional Epithelium. s. The Gastrointestinal Tract as Stomach, Gall bladder, Small and Large Intestine are lined with Simple Columnar. 6. The Acini of Glands as Salivary glands, Pancreas, Sweat glands and Thyroid Follicles are lined with Simple Cuboidal. 7. The Fallopian tubes, and uterus are lined with simple columnar ciliated. The Brain Ventricles and the central canal of the spinal cord are lined with Simple cuboidal ciliated cells. 8. The Male Urethra from inside outwards is lined with : Transitional, Pseudo-Stratified Columnar, Stratified Columnar and then Stratified Squamous. 9. The bony part of Eustachian Tube is lined with Simple Columnar Oliated, while its cartilagenous part is lined with Pseudo-Stratified Columnar Ciliated with goblet cells. 10. The Conjunctival Sac is lined with Stratified Squamous at its exposed parts, while its fornicies, (non-exposed parts) are lined with Stratified Columnar.

III Glandular Epithelium It is the third type of epithelium which is specialised to produce secretion. The glands are formed of collections of epithelial cells. The Different Glands In Our Body Are Classified According To The FoUowing Classifications:

1. According to presence or absence of ducts, the glands are classified into: a) Endocrine or ductless glands, secreting hormones directly in the blood as : Thyroid, parathyroid, pituitary, suprarenal, pineal body, islets of Langerhan 's, placenta, corpus luteum and special cells in the testis and ovary. b) Exocrine glands: They have ducts to carry their secretions. e.g. salivary glands, sweat and sebaceous glands.

-61-

c) Mixed glands, which possess the exocrine ap.d endocrine functions as : pancreas, testis and ovary. 2. According to number of cells, the glands are classified into : a) Unicellular gland as goblet cell which is formed of one cell and is considered as a gland. Goblet cells are present in : Respiratory tract, intestinal tract, pancreatic and bile ducts. .

.

b) Multicellular glands (formed of many cells) as the salivary glands. 3. According to changes in the secretory cells, the glands are classified into: a) Merocrine gland :In these glands there is no cellular changes in their secretory cells; for example : the salivary glands. b ) Apocrine gland :· In which the tips of the secretory cells of the gland are detached and come out with the secretory products of the gland e.g. mammary glands and the axillary sweat glands. c) Holocrine gland : In which the whole secretory cells are destroyed and come out with the secretion e.g. the cells· of the sebaceous glands may come out with their secretion. 4. The glands are classified according to the kind of secretion into : a) Serous secretory glands: as parotid gland and Von Ebner gland of the tongue. b) Mucous secretory glands : as Brunner's gland and goblet cells. c) Mucoserous secretory glands :as submandibular and sublingual glands. d) Fatty secretory glands : as sebaceous glands. e) Watery secretory glands: as sweat glands. f) Waxy secretory glands : as glands of external ear.

g) Cellular secretory glands : as testis and ovary.

-62-

5. According to the shape and branching of the secretory part , of the glands and the shape and i branching of their ducts. Simple The shape of the glands may ubular

"',

,.

be : Tubular, Alveolar or Tubulo-alveolar.

r

'

,,..

".

... .... f

•

~

't .J

!

) ,· ,. . .-· . ~

:

·~

.

..

';.

'.

Gland

i

:

~

,:-·

Tubular Glands

~

.........

~

d) Compound tubular glands : as the kidney and testis.

Acinar Glands. 2. Acinar Glands which may be:

. i· .......

".....

" .

~· I

j

•". . ;.

..,.

• •

J

~

I

-63-

..

#

"'

•

. . .. ..

•

,

..

•

0

:

. .. ' ' ...

...... •

; ,. I /

~

•

, •• • 1' '

'

4

: ' •

~.

~\ ,

......

·..

Ill.

..•

•· ·' Branched "~~. Tubular Gland

•

c) Simple coiled tubular : as the sweat glands.

b) Simple branched Acinar: as the sebaceous and tarsal glands of eyelid.

"'~-:.~

-,~

~.....

b) Simple branched tubular : as the glands of the stomach.

a) Simple Acinar: as sebaceous glands of the skin.

~ ~

.'...

i

,•., .;

1. Tubular Glands which may be: a) Simple tubular glands : as the intestinal glands or the crypts of Lieberkuhn.

'•

,..-~ ..... ,:

"

"\

.._

•

'

c) Compound Acinar: as the sebaceous glands and mammary gland.

Tubulo-Acinar Glands 3. Tubulo-Acinar Glands :which may be:

Compound . .o~ : Tubulo-Acin;·r·.. ' Gland ·,

a) Simple tubulo-acinar: not found in man. b) Branched tubulo-acinar: as the glands of the mouth cavity. c) Compound tubulo-acinar: as pancreas, prostate and salivary glands. 6. The glands can be classified according to their functions into : Secretory and Excretory Gland s. a) Secretory Glands : which synthesize specific substances to be secreted in the body as salivary and endocrine glands. b ) Excretory Glands : which eliminate and excrete the waste products outside the body as kidney and sweat glands.

Neuro-Epithelium It is the fourth type of epithelial tissue (Simple, stratified, glandular and neuro-epithelium). In this type the epithelial cells act as sensory receptors for special stimuli. The neuro-epithelial cells are provided with small hairs (hair lets) on their free ends, while their bases are surrounded with sensory nerves.

-64 -

1. 2. 3.

4.

Neuro-epithelium is found in: Taste buds in the tongue. Organ of Corti in the internal ear (for hearing). the Crista Ampularis in the ampullae of the semicircular canals, in internal ear (for equilibrium). of Macula Utriculi and Macu la Sacculi in the utricle and saccule the internal ear (for equilibrium). P ort· I Tbe tastebud is formed of I ~llilPIIrli n ~ Ct· ll ~ tbe following cells: ~h h·

1. Gustatory or Receptor cells which are also called hair cells or taste cells. They are concerned with taste sensation. 2. Supporting ceUs or sustentacular cells. 3 • Basal CeUs.

( ,u . , tatur~

C dl

~

\

smooth N.H. Tbe Myoepithelial or Basket CeUs are modified ectodermal They muscle cells. They surround the salivary and pancreatic acini. system squeeze the secretion out of the secretory acini into the duct of these glands. the N.H. The Basement Membrane is a tbin layer present between d of epithelial cells and the underlying connective tissue. It is forme the following Two Parts : a) Basal lamina which is formed of glycoprotein. b) Reticular lamina which is formed of (type 4) collagen.

General Characteristics Of Epithelial Tissue nt from 1. Epithelium may arise during embryological developme of ectoderm (as skin and cornea) from mesoderm (as mesothelium the serous membranes) or from endoderm (as the epithelium of the intestinal tract), or from neuro-ectoderm as ependymal cells of brain.

-65 -

2. Blood vessels do not penetrate between epithelial cells except in endocrine glands but nerve fibres can penetrate between the epithelial cells. 3. Epithelium rests on a basement membrane which may be clear or non clear. The non-clear basement membrane is present in: Transitional epith., olfactory epith., thyroid follicles and liver cells. 4. Epithelium can degenerate (destroyed) and can rapidly regenerate (renewed). S. Epithelium has a little intercellular substance but the epithelial cells may Be connected with each other by different types of cellular junctions.

6. Epithelial tissue covers a surface or lines a cavity or forms a gland. 7. Epithelial cells may act as special receptors for taste and equilibrium. N .B. The endothelium is the simple squamous epithelium which lines the heart and blood vessels. The mesothelium is the simple squamous cells of the serous membranes (pleura, peritoneum and pericardium) The mucous membrane is the epithelial lining of any cavity or canal as that which lines the alimentary, respiratory and uro-genital tracts.

Functions Of Epithelial Tissues 1. Protection against injuries, bacteria, chemicals and water as epithelium of skin and stomach. 2. Secretion as glandular epithelium of pancreas, prostate, salivary and endocrine glands. 3. Absorption as the intestinal epithelium. 4. Sensation as the taste buds and organ of Corti. S. Reproduction as the cells of the testis and ovary. 6. Excretion as the cells of kidney and sweat glands. 7. Covering surfaces or lining cavities.

-66-

Connective Tissue Prop er (C. T.) It is a soft type of connective tissue, it is mesodermal in origin. It acts as packing materia l, it support s, binds and connects various tissues and organs. It is formed of connective tissue cells, connective tissue fibres and a soft jelly -like matrix.

Cells Of Connective Tissue Prope r a) Fixed types of connective tissue cells which are long lived stable cells, these cells are: Fibroblasts, Histiocytes (Fixed macrophages), Fat cells (adipose cells),mesenchymal cells, pericytes, endothelial cells and reticular cells. b) Free types of connective tissue cells which enter the connective tissue from the blood, they are short -lived motile cells, these cells sre: Free macrophages, plasma cells, mast cells, and leucocytes.

1- Fixed Cells Of C. T. Prope r 1. Fibroblast It is irregular or fusiform in shape. Its cytoplasm is basophilic and is rich in endoplasmic reticulum, mitocho ndria, Golgi bodies and secretory granules. It has a pale nucleus with dark nucleolus. The old non- active fibroblasts are called Fibrocytes which have an acidophilic cytoplasm and dark nuclei. Functio ns Of Fibroblasts They form C. T. fibres and the C. T. matrix. They help in closure and healing of wounds.

-67-

Fibroblasts

2. Histiocytes (Fixed Macrophages) They have irregular cell membranes. They have darkly - stained nuclei. Their cytoplasm is rich in lysosomes, phagocytosed bodies and residual bodies. Histiocytes can be stained with vital stains as indian ink.

Macrophages

Functions Of Histiocytes: They can phagocytose and digest foreign bodies . They can trap and transport antigens. Histiocytes can fuse with each other to form a Giant cell which has a high phagocytic function to bacteria.

3. Fat Cells (Adipose Cells)

r

They are rounded or oval in shape. They have peripheral flattened nuclei. They have thin rim of cytoplasm under the cell membrane. Each fat cell is filled with a large central droplet of fat which appears as electron - dense mass.

Functions Of Fat Cells They act as storage house of fat. They support and protect certain organs as kidneys. They act as heat insulator.

Fat Cells

4. Mesenchymal Cells It is an embryonic undifferentiated mesenchymal cell.

It has a pale cytoplasm with central oval nuclei. Its cell membrane is irregular with multiple processes.

-68-

, Mesenchymal

Cells

The cells are usually surrounded with jelly-like matrix. Functi ons of mesenchymal cells: They can be differe ntated to adult connective tissue cells.

5. Pericytes They are presen t in the wall of blood capillaries between their basem ent membr ane and their endothelial lining. They have irregular cell membr ane with multiple processes and oval nuclei. Functi ons of Pericytes: They can be changed to fibrobl asts, to smoot h muscle cells during repair of C.T. and blood vessels. They act as myoepithlial cells that may contra ct and constrict bood capillaries.

6. Endothelial Cells

They are mesodermal in origin. They are flat simple squam ous cells with flat nuclei. They line the blood vessels and blood capillaries. Functi ons Of Endoth elial Cells They can form (type 4) collagen. They form the collagen of the capillary basem ent membr ane. They can divide to forin new blood capillaries.

Endothelial Cells

H

7. Reticular Cells They are modified fibroblast Cells which form reticulin. They have irregular cell memb rane with multiple processes. Functi ons of reticular cells Reticu lar cells and reticular fibres form a networ k in the stroma of organs as bone marrow , spleen and lymph nodes.

-69 -

Reticular cells when stimulated by antigens they change into phagocytic cells. They can remove cellular debris from lymphatic tissue.

II - Free Cells Of C. T. Proper 8. Plasma Cells Plasma cells develop from BLymphocytes of the blood after their migration from blood to C.T. It is a rounded cell with rounded eccentric Plas rna Cells nucleus and clear large nucleolus. The chromatin material of the nucleus is condensed near the nuclear membrane giving a cartwheel appearanc e. It has a basophilic cytoplasm rich in endoplasmic reticulum, mitochondria and Golgi bodies. Golgi body is not stained with basophilic stains, therefore its place appears non-stained and is called negative Golgi image. Functions of plasma cells They can produce antibodies. They defend the body against infection. Lymphocytes and plasma cells play an important role in raising the immunity of the body.

9. Mast Cells It is an oval cell with basophilic granular cytoplasm. It has a small eccentric rounded nucleus. The granules are rich in heparin, they can be stained purple with methylene blue stain. This reaction and change of colour is called metachrom asia.

-70-

''

. .: '

Mast Cells

Functions of mast cells The granules of mast cells are rich in heparin and histamine. Heparin prevents blood clotting and agglutination of blood platelets. Histamine dilates blood vessels and increases the permeability of blood capillaries.

10. Pigment Cells Or Melanophores They are C. T. macrophages which phagocytosed pigment granules They are branched cells with multiple processes. Their cytoplasm is rich in melanin granules called melanosomes. Sites: They are present in the dermis of skin. Functions: They carry melanin pigments.

11 - Leucocytes They are blood leucocytes which migrate from the blood stream to connective tissue, their number increases in the C.T. when there the is infectio n to phagocy tose micro-organisms. These blood leucoytes are: Neutrop hils, Lympho cytes, Monocy tes, Eosinophils and Basophils.

Neutroph ils

Eosinophil

Lymphoc ytes

12 - . Free Macrophages Blood monocytes during infections migrate to C.T. and then change into Free Macrophages. They are branched cells with irregular cell membrane. They have oval eccentric nuclei. Their cytoplasm is rich in lysosomes and foreign bodies. Functions They are phagocytic cells. They share in the immune system of the body.

-71-

-

They secrete collagenase, elastase enzymes and lysozymes;

Connective Tissue Fibres 1. White Collagenous Connective. Tissue Fibres -

White CoHagen Fibres are flexible but not elastic. They appear as white bundles. The bundles branch, while the fibres do not branch. Each collagen bundle is formed of fibres, each collagen fibre is formed of fibrils, each fibril is formed of tropocollagen molecules. Formation of different types of collaaen

Type I collagen is present in muscle tendons and is formed by fibroblasts and osteo blasts. Type D Collagen is present in the cartilage and is formed by chondrob lasts. Type m Collagen is present in blood vessels and is formed by smooth muscle cells. Type IV Collaaen is present in the basement membranes and is formed by epithelial cells. Type V Collagen is present around muscles and is formed by muscle cells. Collagen fibres are stained blue by Mallory's stain.

2- Yellow Elastic C.T. Fibres

-

They are thin, branching strechable fibres. Each fibre is formed of a central mass of protein called elastin surrounded by micro fibrils. They are formed by fibroblasts and by smooth muscle cells. They are digested by pancreatic elastase. They can be stained brown with orcein stain.

3 - Reticular C.T. Fibres -

They are delicate fibres which form networks in the stroma of glands and organs as liver and spleen.

-71-

They are considered as type 3 collagen fibres which are formed by fibroblasts and smooth muscle cells. They can be stained dark brown with silver stain .

Ill Matrix Of Connective Tissue Proper It is a jelly-like substance formed of acid mucopolysaccharide. It is formed by the fibroblasts. It is present between the C.T. cells and C.T. fibres. It allows diffusion of tissue fluid, nutrients and waste products between the tissues of the body.

Types Of Connective Tissue Prope r

\

C.T. C.T. Adipose C.T. Reticular White Collagenous C.T. C.T. Yellow Elastic C.T. Mucous

1. Loose areolar

2. 3. 4. 5. 6.

Mast Cell

Fibrob last

~

-...Lymphocytes

Areolar C.l

1 - Loose Areolar Connective Tissue It is present all over the body, it binds tissues together and surrounds organs. It is not present between nerve cells of the brain. It is formed of C.T. cells and C.T. fibres which are embedded in a loose matrix. Fibroblasts and macrophage cells are the most common cell type

in loose areolar C. T. Sites. 1. Aroun d organs and blood vessels. 2. Subcutaneous connective tissue. 3. Submucosa. 4. Serous membranes as pleura, peritoneum and pericardium.

-73 -

2 - Adipose Connective Tissue Its structure is similar to that of areolar C. T., but it is very rich in Fat cells (Adipocytes).

~Fat Cells

Types Of Adipose C. T. A -

White Adipose C. T.

It is formed of large fat cells, each fat cell contains one large globule of fat. It appears yellow because it contains carotene pigments.

Adipose C.T ..

Sites of white adipose C.T. 1. Under the skin, mammary glands and gluteal regions. 2. Around the kidneys and blood vessels. 3. In the omentum and abdominal wall. Functions

1. Acts as heat insulator and as fat storage areas in the body. 2. It supports the kidneys and other organs.

B- Brown Adipose C.T It is formed of fat cells, each fat cell is filled with multiple fat droplets. It appears brown because it is rich in blood vessels and pigments.

Sites of brown adipose C.T. 1. Mainly in foetuses and new born infants. 2. In the scapular, axillary and mediastinal regions. Function It provides heat for new born babies.

N.B. Adipose C.T. Is Not Present In The Following Areas: Eyelids,Lungs, Penis, Labia Minora, Clitoris and Nipples.

3 - Reticular Connective Tissue marrow, glands and It forms the stro ma or framework of bon e organs. It is Formed of: genous fibres. a- Reticular fibres which are thin immature colla haped cells with b- Reticular cells which are branched stellate-s multiple processes. cellular junctions. The cells are connected with each other by interReticular cells are modified fibroblast cells. Sites Of Reticular C. T. : rk (stroma) of : Both reticular cells and fibres form the framewo ovary and kidney. Bone marrow, spleen, lymph node, liver, testis,

Elastic membranes

Reticular C. T·.

Elastic C. T.

4 - Yellow Elastic Connective Tissue It is an elastic stretchable type of C. T.

It is yellow in colour in fresh condition. It can be stained brown with orcein stain. s sepa rate d with It is formed of condensed regular elastic fibre fibroblast cells. Sites Of Elastic C.T . d flow). Aor ta and arteries (to maintain continuous bloo Lung, bronchi, bronchioles and alveoli.

-7 5-

Ligamentum flavum (between vertebrae), Ligamentum nuchae (in the back of the neck) to facilitate trunk and neck movements. Suspensory ligament of penis (to facilitate erection).

5 - White Collagenous Connective Tissue It is a white dense type of C. T. _ It is formed of collagenous C. T. bundles separat ed with fibroblast cells and areolar C. T. It has a small amount of matrix and it is poor in blood supply. Types OF White Collagenous C. T.

1-

Regula r Dense White Collagenous C.T. '

It is formed of regularly arrange d collagenous bundles separated with cells (Tendon cells). These tendon cells are stellate-shaped with oval central nuclei..

Sites of regular white C.T. Tendon of muscles and ligaments. Cornea of the eye.

7t

C.T. Bundle

2. Irregula r Dense White Collagenous C.T. It i~ formed of irregularly arranged collagenous C.T. bundles separated with fibrobla st cells and little matrix. Sites

Fibrobl asts

~

t

L.S. In Tendo n

Regular Collage nous C. T.

Deep fascia and dermis of skin. Capsule of lymph node, .spleen and liver. Perichondrium (around cartilage) and Periosteum (around bone). Sclera of eye ball. Dura mater which is a covering protecting membra ne to -76-

Irregula r White C.T.

the brain.

6 - Mucoid (Mucous) Connective Tissue is presen t mainly in embryonic tissue. It is formed of 1. Matrix which is a soft jelly-like substance rich in mucin. 2. Muco id cells which are mesen chyma l cells with communicating processes. 3. Very fine collagenous fibres. It

Mucoid

C.T.

Sites of Mucoid C. T. 1. Umbilical cord of the embryo between its two arteries and its vein, it is called Warto n jelly. 2. Vitreous humour of eye. 3. Pulp of growing teeth. Functions Of C. T. Proper 1. It supports and connects organs and tissues. 2. Through C.T. proper blood vessels, nerves and lymph vessels are present to supply the different parts .of prgans. 3. There are specific functions for C.T. cells as: a) Production of antibodies by plasma cells. b) Production of histamine by mast cells. c) Phagocytic functions of histiocytes and blood leucocytes. d) Formation of C. T. fibres and C. T. matrix by fibroblast cells during growth and repair of tissues. e) Storage of fat by fat cells. 4. C.T. is very important for groWth of tissue and healing of wounds.

-77 -

Cartilage It is a firm

type of connective tissue. It is flexible and strong. Functions of cartilage:

----=-- - -

..

...

--...... -.. .. - - ... •

-

.... - ~ Chondroblast ..

.. ..

It facilitates movements of "' .... -. Matrix joints. ,. • • • It keeps respiratory • # · • Cell Nest passages patent day and • night. • .. • / C a r t i l a g e Cells It is responsible for the growth of bones in length Hyaline and width. Cartilage

-

Structure of cartilage: Cartilage is formed of cartilage cells, connective tissue fibres and matrix. Cartilage Cells are the chondroblasts and chondrocytes.

1. Chondroblasts They are oval cells with basophilic cytoplasm and pale oval nuclei. They are present singly under the perichondrium. They have many rough endoplasmic reticulum, Golgi bodies and ribosomes. They develop from embryonic mesenchymal cells. They form the protein and type 2 collagen fibres of the matrix. When chondroblasts are surrounded with lacunae they are called chondrocytes.

2. Chondrocytes They are irregular in shape with basophilic cytoplasm and central rounded dark nuclei.

-78-

Young chondrocytes can divide, so they are present in groups surrounded by spaces called lacunae. These groups are called cell nests. Their cytoplasm is rich in glycogen and phosphatase enzymes. It has well-developed endoplasmic reticulae. They form protein and type 2 collagen of the matrix. The Connective Tissue Fibres present in cartilage are: - Collagenous fibres (type 2). - Elastic fibres. Matrix or Ground Substance Of Cartilage: It is rubbery in consistency and homogeneous in appearance. Its protein is formed by chondroblasts and chondrocytes. Its protein is of 2 types: a) Chondro-mucoprotein (Protein polymer) b) Chondroitin sulphate which causes the basophilia of the matrix.

Types Of Cartilage 1. Hyaline Cartilage with clear basophilic matrix. 2. Elastic Cartilage with many elastic fibres. 3. White Fibro - cartilage with many collagenous fibres.

I- Hyaline Cartilage Sites: 1. 2. 3. 4.

Costal Cartilage. Cartilage of the nose, larynx, trachea and bronchi. Long bones of foetal skeleton. Articular surfaces of joints.

Structure: It is formed of a homogeneous matrix which is formed of 2 types

of protein with white and elastic connective tissue fibres which are not apparent by the ordinary stains .

.-79-

Two types of cartilage cells are embedded in the matrix: a) Chondroblasts under the perichondrium (mention their characteristics). b) Cbondrocytes present in the centre and in groups (mention their characteristics). Hyaline cartilage is covered by perichondrium except at the articular surfaces of joints. The Perichondrium Is Formed Of 2 Layers: a) Outer Fibrous Layer formed of collagenous fibres, fibroblasts and blood vessels. b) Inner Chondrogenic Layer formed of chondroblasts. Functions Of Perichondrium 1. It supplies the cartilage with blood and nourishment. 2. Muscles are attached to the perichondrium. 3. Chondroblasts and chondrocytes are responsible for the growth of cartilage.

II - Elastic Cartilage Sites: 1. Ear pinna. 2. External auditory tube. 3. Eustachian tube. 4. Epiglottis. 5. Corniculate, cuneiform and arytenoid cartilages of the larynx. Characteristics of Elastic Cartilage: It is similar to hyaline cartilage but: a) The matrix is rich in elastic fibres which surround the cartilage cells. b) Elastic cartilage is more flexible.

-80-

III - White Fibro - Cartilage Sites: 1. Intervertebral discs. 2. Semilunar cartilages of knee joints. 3. Symphysis pubis, acetabulum and glenoid cavity. 4. Discs of sterno - clavicular and tempro - mandibular joints. S. Terminal parts of muscle tendons and tendon grooves.

.

.

Characteristics Of White Fibro - Cartilage - It is not surrounded by perichondrium. The chondrocytes are arrang_ed in rows or columns. The rows of cartilage cells are separated with acidophilic collagenous bundles and acidophilic matrix penetrated by B. V.

Bone Bone is formed of solid matrix, bone cells, periosteum and endosteum. Bone Matrix is formed of packed layers of calcified collagenous lamellae embedded in osteoid tissue. Bone matrix is formed by osteoblasts and is maintained by osteocytes.

Bone Cells 1 - Osteogenic Cells Or Osteoprogenitor Cells They are mesenchymal stem cells found in periosteum and endosteum. They are oval elongated cells with pale cytoplasm and oval nuclei They can divide and can differentiate into osteoblasts in vascular tissue and into chondroblasts in non-vascular tissue.

2 - Osteoblast Cells They are oval cells with eccentric rounded nuclei. They have deep basophilic cytoplasm with many ribosomes and endoplasmic reticulum.

-81-

They contain phosphatase enzyme to deposit calcium and pyrophosphatase enzymes which inhibit the action of pyrophosphates. They form the components of matrix. They are present mainly in the periosteum and endosteum. Osteo blasts change into osteocytes when they are trapped inside lacunae

3 - Osteocytes They are small cells with basophilic cytoplasm. Each osteocyte occupies a small cavity called lacuna. Canaliculi arise from these lacunae to communicate osteocytes via filopodial processes. They cannot divide, so they are present singly in each lacuna (they are not present in cell nests). Osteocytes maintain bone matrix, they form the collagen and proteoglycan substances.

4-

Osteoclasts

They are bone phagocytic cells, they are formed by fusion of blood mono cytes or osteopro genitor cells or macrophages. They are large cells with acidophilic foamy cytoplasm and ruffled cell membrane ~?order. Each cell has many nuclei up to 20 nuclei. They are present at bony surfaces

Three

Osteoclast Cells

in depressions called Howship's lacunae. Osteoclasts have irregular borders. They are responsible for remodeling of bone during bone formation.

-82-

Microscopic Structure Of Com pact Bone 1. Periosteum It is a vascular C.T. membrane which covers the bone from outside. It is formed of the following 2 layers: a) Outer fibrous layer of collagenous fibres, fibroblasts and B. V. b) Inner cellular layer of osteogenic cells and osteoblast cells. 2. Endosteum It lines the inner surfaces of bone. It is formed of osteogenic cells and osteoblast cells.

l. Haversian System or Osteon It is the structural unit of compact bone. Each system is formed of Haversian canal, bone lamellae and osteocytes.

•'

,•

•/ ; . ·

· ·' > . ..

Haversian · System Haversian Canal

a) Haversian canal: It runs .....=--c=-- -ln tersitial parallel to the long axis of . System bone. It contains C. T., B.V. and nerves. Compact Bone (Decalcified) b) Bone lamellae. They are from 5 to 20 concentric layers of calcified osteoid matrix. c) Osteocytes. They are surrounded with lacunae, the canaliculi arise from these lacunae. The cells are embedded between the concentric bone lamellae. 4. External Circumferential lamellae; These are the bone lamellae with their osteocytes which run close to the periosteum. 5. Internal Circumferential Lamellae; These are the bone lamellae with their osteocytes which are close to the endosteum.

-83-

6. Interstitial Lamellae; These are the irregular bone lamellae with their osteocytes which are present inbetween the Haversian systems.

7. Volkman's Canals; These are transverse canals which connect some Haversian canals together, through these canals blood vessels can anastomose with each other. 8. Sharpey's Fibres These are the calcified ends of the muscle tendons which extend from the tendon to the periosteum then to the bone lamellae. Types Of Bone, Compact and cancellous:

1. Compact Bone present in the shafts of long bone and in the outer covering of flat bone.

2. Spongy or Cancellous Bone present in the ends of long bones, ribs, vertebrae, in the centre of flat bones as Skull, Scapula, Sternum and Sacrum.

Characteristics Of Spongy Or Cancellous Bone ~·

e

• •

~ Bone

It · is formed of . , . Trabeculae irregularly arranged plates of branching bone trabeculae. Bone The bone trabeculae Marrow are formed of irregular bone lamellae with scattared osteocytes which are em bedded between . - . Marrow bone lamellae. There is no Haversian system. Spongy Bone Multiple bone marrow cavities are present between the bone trabeculae. -84-

Red active bone marrow is present in the bone marrow cavities. Bone cells are nourished by the diffusion of tissue fluid from the blood vessels of the bone marrow cavities.

Ossification Of Bone Bone is formed by the foUowing two methods:1. Intramembranous Ossification which is characterized by; It occurs in bones of skull and clavicle. The mesenchymal cells change into osteogenic cells. The osteogenic cells change into osteoblast cells which form the calcified bone matrix. The formed bone matrix extend as bone trabeculae enclosing between them multiple bone marrow cavities. This form trabeculae of bone with scattered osteocytes embedded in their calcified matrix this membranous ossification gives rise to spongy bone. - The osteogenic cells on the surface differentiate into osteoblast cells which form the periosteum and endosteum.

Cartilagenous Ossification Articular Surface .-Resting Stage

-Proliferative Stage -Hypertrophy Stage -Calcification Stage Degenerative Stage · -- Bony Collar -Spongy Bone Formation - Formation Of Haversian Systems

-85- .

2. lntracartilagenous Ossification which is characterized by:

1.

l. 3. 4. 5.

6. 7. 8.

9.

It occurs in the long bones which were originally hyaline cartilage in the foetus. This hyaUne cartilage wiD be replaeed by bone through the following steps:; Resting stage of hyaline cartHage is present in the region of growing zone of the long bone. ProUfentive stage of cartHage eells in which there is an increase in the number of cartilage cells. Hypertrophy stage of cartHage eells in which there is an increase in the size o( cartilage cells. Caldfieation stage of the matrix around the cartilage cells and under the perichondrium. Degeneration of the eentnl cartHage eells. The peripheral calcified matrix prevent blood supply from reaching to the central cartilge cell, so they will die leaving empty spaces. Stage of invasion of the empty spaces by vascular tissue rich in osteogenic cells and blood capillaries. Stage of Spongy bone formation: The osteogenic cells change into osteoblasts which form trabeculae of spongy bone. Stage of remodelling which is done by osteoclast cells. These cells are collections of monocytes. They secrete osteolytic enzymes which destroy the centr81 irregular trabeculae of spongy bone. Stage of development of Haversian systems. Osteoblasts start to form concentric calcified bone lamellae around blood vessels forming longitudinal canals with central B.V. (Haversian canals). The osteoblasts change into osteocytes when they are trapped with calcified osteoid tissue. This process goes ·on several times untill mature Haversian systems are formed.

N.B: Formation of bone during growth and during repair of bone fractures is controlled by; Vitamin D, Vitamin C, Vitamin A, level of calcium in the blood, Parathyroid hormones, Calcitonin hormone and Growth hormone.

-86-

Muscular Tissue These are the types of muscles in the body : 1. Smooth visceral involuntary plain muscles. 2. Striated skeletal voluntary muscles. 3. Cardiac striated involuntary muscles.

Muscle cells are long and are separated by connective tissue, so they are called muscle fibres.

Smooth Muscles They are spindle-shaped cells with central oval nuclei. Their cytoplasm is homogeneous with no striations. They contain many long actin and few short myosin filaments. They contain all cell organoids and cell inclusions. Smooth muscle fibres are connected with each other by gap junctions through which electrical impulses can pass. Smooth muscles are mesodermal in origin except those of iris of eye. They regenerate from the pericyte cells present around blood vessels. They contract by translocation of actin and myosin filament after cleavage of A TP. Sites of smooth muscles : 1. 2. 3. 4. 5. 6.

Digestive system; gastro-intestinal tract. Respiratory system; trachea, bronchi and bronchioles. Urinary system; "ureter, urinary bladder and urethra. Male and female genital system. Tunica media of blood and lymph vessels. Capsule of spleen, lymph nodes and digestive glands.

-.,. ,

,.

..,.

.,..

,f11/!l'

,

,

.,..

..

Smooth

Muscles

~

-87-

Skeletal Muscles They are attached to the skeleton of the body. They show transverse dark and light bands called striations. They are present all over the body attached to the skeleton and in the diaphragm, tongue, eye and upper third of oesophagus. The connective tissue around the whole muscle is called epimysium. The C.T. around the muscle bundles is called perimysium and between the muscle fibres is called endomysium. Skeletal muscle cells are long and cylindrical and are called muscle fibres. Their nuclei are multiple, long and peripheral in position. The cell membrane of skeletal muscle cell is called sarcolemma. The cytoplasm is called sarcoplasm, it contains all organoids and inclusions. C.T Perimysium Parallel myofi brils are present in the sarcoplasm, they are of 2 types:

+

a) Thick myosin filaments in the A bands. b) Thin actin filaments in both I and A bands. Each myofibril shows alternating dark or A-bands (Anisotropic) and light or I bands (Isotropic).

v,...;:=~:c

Skeletal Muscle (T.S)

The dark A band shows a pale area in its centre The light I band shows a dark area in its centre

= H Zone. = Z line.

The distance between two Z-lines is called Sarcomere. The Sarcomere is the functional and structural contractile unit of the muscle fibre . It is formed of actin and myosin filaments .

-88-

During muscular contraction, the thin actin filaments glide over the thick myosin filaments resulting in shortening of the sarcomeres. Characteristics Of The Sarcolemma: -

It is the cell membrane of the muscle fibre. It plays a role in conducting the impulse to muscle fibre through 3 types of tubules called Triad Tubular System.

The Triad Tubular System is formed of the following: 1. One Transverse Tubule which is formed by a transverse invagination from the sarcolemma to the depth of the cytoplasm. 2. Two Sarcoplasmic Tubules. These are two modified tubules of the endoplasmic reticulum surrounding the transverse tubules from its both sides. These tubules pump calcium ions between myosin and actin moleules resulting in their connection and disconnection giving rise to muscular contraction.

Striations Peripheral Nuclei Sarcolemma

Fibre (Low)

Skeletal Muscle (L.S.)

(High)

Cardiac Muscle The wall of the heart is formed of: • Striations 1. Epicardium formed of simple squamous ' -'" Branching ~ Cardiac epithelium and areolar Muscle C.T. Fibres 2. Endocardium is formed of: a) Simple squamous endothelium. \ b) Areolar connective tissue. Cardiac Muscle Fibres c) Elastic membrane. d) Areolar C. T with blood vessels and Purkinje fibres.

- -

3. Myocardium formed of cardiac muscle fibres.

Characteristics Of Cardiac Muscle Fibres The fibres are short, they branch and join each other to form a network. They have cross striations. They have oval prominent central single nuclei. Cardiac muscle fibres are joined together by intercalated discs. They have large numerous mitochondria. Their T-transverse tubules are present at the Z-lines. They have 2- Tubular system instead of Three tubular system. Each T-tubule is in direct contact with only one tubule of the endoplasmic reticulum. Gap junctions are present between cardiac muscle fibres, through these gaps, ions and electrical impulses can pass. The Heart Valves are formed of dense C.T. rich in collagen and elastic fibres. They are lined on both sides by simple squamous endothelium.

-90-

Impulse Conducting System Of The Heart These are the sinoatrial node (S-A node) or pacemaker of the heart . . Atrioventricular node (A- V "node); atrioventricular bundle of His. (A - V bundle) and Purkinje fibres. These nodal cardiac cells are smaller than cardiac muscle cells. They have few myofibrils. They are concentrically arranged around large nodal arteries. The atrioventricular bundle of Hiss is formed of Purkinje cell fibres .

Characteristics Of Purkinje Fibres Of The heart They are noncontractile modified cardiac muscle fibres. They extend in the interventricular septum to the ventricular walls. They are thick fibres with large diameters. They contain few peripheral myofibrils. Their sarcoplasm is rich in glycogen and mitochondria. They have no T -tubular system. Purkinje fibres are connected by desmosomes and by gap junctions .

.

:: :. . : ~ Cardiac Muscle Fibres :)l, -•·. ._ :·

..... . . . . ..

·:'tt ""'

~:~~~

Blood Capillary

Moderator Band (T .S) -91-

Nervous Tissue The Neurone It is the structural and functional unit of nervous system. It is formed of a nerve cell and its processes (axon and dendrites).

Satellite Cells --"'!"-·Unipolar Nerve Cells

The Nerve Cells Size: varies from small cells as in cerebellum and large cells as in cerebrum. Shape: According to the number of their processes, neurones are classified into: 1. Pseudo-unipolar Neurones; found in

spinal and cranial ganglia. 2. Bipolar Neurones; found in retina, olfactory mucosa, cochlear and vestibular ganglia of the internal ear. 3. Multipolar Neurones; They are of 3 subtypes:

Nerve ~-Cells

In Spiral Ganglion

a) Stellate-shaped N eurones as those in sympathetic ganglia and anterior horn cells. b) Pyramidal-shaped Neurones as those of cerebral cortex. c) Pyriform-shaped Neurones as Purkinji Multipolar Nerve Cell cells of cerebellum. Structure of Nerve cells: The cytoplasm contains: the following organoids and inclusions: 1. Their cell membranes are very thin. 2. Ribosomes and endoplasmic reticulum form Nissl bodies.

-92-

Cerebellum

3. Golgi apparatus surrounds the nucleus. 4. Mitochondria are scattered in the whole cytoplasm. Non· 5. Lysosomes; Their number increases wirh ·Stained age. Axons 6. Lipofuscin pigments; their amount ......_..,...__ o increases with age. 7. Neurofibrils and neurotubules are Nerve Trunk (Osmic Acid Stain) scattered in the whole cytoplasm. 8. Melanin granules are present in certain nerve cells (substantia nigra of midbrain). 9. Glycogen and lipid granules act as local sources for energy. 10. Centrosomes are not present in mature nerve cells therefore they do not divide. The Nucleus has a thick nuclear membrane and clear nucleolus.

The Dendrites Of Nerve Cells They are extensions of the cell body. They conduct nerve impulses towards the cell body. They contain most of cell organoids and inclusions. Their terminals have dendritic spines or gemmules for synaptic connections.

The Axon Of Nerve Cell It is a single long extension of

the neurone. It arises from the nerve cell by a conical area called axon hillock. Through its length it gives collateral branches. At its termination it forms multiple arborization. Its cell membrane is called axolemma . .

-93-

Its cytoplasm is called axoplasm. Types of Axons according To The Covering Sheath. Axons may be naked (not covered with myelin sheath or neurolemma as those nerves present in grey matter). Axons may be covered with myelin sheath but with out neurolemma as those nerves present in white matter and optic nerve. Axons covered with myelin sheath and neurolemma as peripheral nerves outside the spinal cord. Axons covered with neurolemma but without . myelin sheath as post-ganglionic S . G : p•na1 ang110 0 (Hx & E) sympathetic axons. •

t

Types of Neurones According To The Length Of Axons: 1. Golgi Type I Neurones: They have long axons as nerve axons in the brain and spinal cord tracts. 2. Golgi Type II Neurones: They have short axons as those in the cerebellum and retina. Types Of Neurones According To Their Functions: 1. Motor Neurones as those of anterior horn cells. 2. Sensory Neurones as those of posterior root ganglia and posterior horn cells. 3. Associative Intemeurones which connect the motor and sensory neurones in the brain and spinal cord. The Myelin Sheath: It is a lipoprotein substance formed by the rotation of the formed myelin around the axon. This myelin is formed by neurolemma! cells.

-94-

It is interrupted at intervals by Nodes of Ran vier. It acts as insulator for nerve impulses. It dissolves by alcohol, it stains black with osmic acid. Neurolemmal Or Schwan Cells -

They They They They

form a chain of cells around the myelin sheath. form the myelin sheath around the axons. help in regeneration of cut neurones. act as insulators for nerve impulses.

Tbe Synapse It is the point of contact between processes of neurones. Types Of Synapses:

1. Axo-deadritic: between axons of a neurone and dendrites of · aaother. l. Axo-somatic: between axon of a neurone and a cell body of another. 3. Axo-axoaic: between 2 axons of 2 neurones. The Area Of Synapse Is Formed Of: 1. Terminal Bouton of the axon, it is rich in acetylcholine, adrenaline, noradrenaline and dopamine. l. _Presynaptic Membraae: It is the membrane of the terminal bouton of the axon. 3. Synaptic Oeft, it is the area between pre - synaptic membranes of the axonal bouton and the post - sysnaptic membrane of the dendrites. 4. Postsynaptic Membrane, it is the cell membrane of the target neurone· at the site of synapse. 5. Gemmules or Spines, are the small projections of the pre and post synaptic membranes.

-95-

Nerve Ganglia They are collections of nerve cells and fibres outside the C.N .S (Central Nervous System). These are the different types of ganglia: 1. Sensory Craniospinal Ganglia: They are attached to some cranial nerves and to all spinal nerves. 2. Autonomic Motor Ganglia: They are the sympathetic and parasympathetic ganglia.

Characteristics Of Spinal Ganglia: They are covered with thick connective tissue capsules. They are formed of large pseudo-unipolar neurones. The nerve cells are found in groups. The nerve cells are separated by myelinated nerve fibres. Presence of supporting satellite cells around the neurones. No Synapses are present between its neurones. The processes of each nerve cell form a glomerulus inside the cell body of the neurones.

Characteristics Of Sympathetic Ganglia (Autonomic Ganglia) They are covered with thin Capsule connective tissue capsules. Multipolar They are formed of small Nerve Cells stellate-shaped multipolar nerve cells. The nerve cells are Satellite Cells scattered, not arranged in groups. The nerve cells are separated . by nonmyelinated nerve fibres. Sympathetic Ganglion Presence of few sattelite cells around the neurones. Synapses are present between the neurones.

-96-

Neur oglia They are special supporting cells for peripheral and central nervous system. s A) Neuroglia - like cells which are present in the peripheral nervou system are: , 1. Schwan Cells are present aroun d the axons of peripheral nerves they form the myelin sheath and help in regeneration of cut nerves. 2. Sattelite cells surrounding neurones of ganglia. 3. Epend ymal simple cuboidal ciliated cells lining brain ventricles. 4. The Tanac yte cells which suround the neurones of hypothalamus. 5. Spongioblast cells which are primitive cells, they can differentiats into neuroglia and ependymal cells. B) Neuroglia Prope r which are present between the neuro nes of the central nervous system, they are of the following types:1. Protop lasmic Astrocytes They are present in the grey matter. They are ectodermal in origin. Their cytoplasm and processes are granu les in glio some rich (lysosomes). They have no axons, no Nissl's granules. . Q les therefore they centno 2 have They can divide giving brain tumours. Their processes end aroun d blood vessels. 2. Fibril lar Astrocytes

Protoplasmic Astrocyte

Fibri llar Astro cyte '

They are similar to protoplasmic astrocytes But: They are present in the w bite matte r 0 and are ectodermal in origin. Their cytoplasm and processes are rich in microfilaments. -97 -

3. Microglia

-

They are mesodermal in origin. They are present in grey and white matter. They are small spindle-shaped cells with few processes. They have no Nissl's gr~nules, no centrioles, they cannot divide. They are phagocytic cells for micro-organisms.

Microglia

4. OUgodendrocyte They are present in the grey and white matter. They have few short thick processes. They form the myelin sheaths of the axons of the C.N .S.

OHgodendroglia ·

Functions Of NeurogHa

-

They suppcrt the neurones .. They form the myelin sheaths. They act as insulators between neurones. They help in the nutritive functions of neurones (as astrocytes). They phagocytose foreign bodies and micro-organisms (as microglia) They help in regeneration of neurones (as Schwan cells).

-98-

Degeneration Of Neurones If the axon of a neurone is cut or injured the following changes occur: 1. Retrograde degeneration occurs in its cell body. l. Traumatie degeneration occurs at the site of injury. 3. Wallerian degeneration occurs at the peripheral part of the axon. Changes In Tbe Nerve Cell During Retrograde Degeneration:

1. The nerve cell swells, loses its dendrites and becomes oval. 2. Nissl's granules become smaller in size, fewer in number and then disappear (Chromatolysis). 3. The cytoplasm becomes pale and rich in vacuoles. 4. Neurofibrils, Golgi apparatus and mitochondria degenerate and become fragmented. S. The nucleus becomes pyknotic (shrunken) and eccentric (peripheral). Changes In The Axon During Wallerian Degeneration: The axon becomes swollen at interrupted areas (beaded appearance). The axon then becomes segmented. Th~ myelin sheath becomes segmented and rich in fermentation chambers .. The neurolemma! cells increase in size and number to form a covering layer over the cut end to help in regeneration processes. N.B. Traumatic Degeneration is a rapid process of Wallerian degeneration at the site of injury. Regeneration of neurones can occur 'if the wound is clean, if the neurolemma is intact and if the axons are partialy injured.

Nerve Endings They are of l types: 1. Receptors or Sensory nerve endings. 1. Effectors or Motor nerve endings.

-99-

Receptors 1. Special Sense Receptors Are:

Retina in the eye for reception of vision. Organ of Corti in internal ear for reception of hearing. Olfactory epithelium in nose -for reception of smell. Taste buds in tongue for reception of taste. Crista ampularis and maculae utriculi and sacculi in the internal ear for reception of changes in posture. 2. Skin Receptors for pain, temperatu re and touch. 3. Visceral Receptors from the wall of stomach, bladder and other viscera. 4. Propriocep tors from skin, muscles, tendons and joints. a) b) c) d) e)

Non-Capsulated Receptors In Epithelial Tissue. Receptors In the Epidermis Of Skin Are: 1. Free Nerve Endings for pain, touch and temperature. 2. Merkel's Discs for sensation of light touch. 3. Peritrichial Nerve Endings surrounding hair follicles for light touch and hair movements.

Capsulated Nerve Endings In Connective Tissue. Receptors In C. T. Dermis Of Skin. 1. Meissner's Corpuscles for discrimin ation tactile (distinguishing between two near pointed pricks). 2. Krause's End Bulb are mechanoreceptors for touch, pressure and cold sensation. 3. Ruffini End Organ for hot sensation and mechanical movements of the joints.

-100-

Epidermis of Skin

~....;;--""'!:"'

Meissner Corpuscle In .....,......._. Dermis

4 -

Pacinian Corpuscles

In ~onnective tissue of: skin panc reas, stom ach mamm ary glands, skeletal tendo ns, musc les, ligam ents, joint s and external genitalia. Structure: Concentric layers of Schwan and fibrob last cells with centr al non- myel inate d nerve fibres. Functions: It responds to deep pressure, vibra tion sense , tactil e localization, tactile discriminatio n and stereognosis (Knowing things by touch).

Sites:

~apusle

Concentric

~aiJ!ellae

"'

- .~erve o,

Pacinian

I

Corpu~cle

Nerve Endings In Muscles And Tendons

1 These are Pacin ian Corpuscles, Muscle spindles, Tend on spind or Golgi Tend on Organ and Moto r-end plate.

Muscle Spindles Sites:

,

Flexor muscles of upper limb. Extensor muscles of lower limb. Muscles of back, hands, feet and intercostal muscles. •

1 \

/

:

Extrafusal Muscle Fibres

~

• I

- 101-

Func tions : They convey infor matio ns to the brain to maint ain the muscle tone, body postu re and to coord inate volun tary movements. Struc ture: It is covered with C.T. Capsu le, it contains the following intraf usal muscle fibres: a) Nucle ar bag muscle fibres conta in static and. dynamic fibres . The dynamic bag fibres are inner vated by dynamic gamm a axons . b) Nucle ar chain muscle fibres conta in a row of nuclei and are inner vated by Static gamm a axons. The sensory nerve endings of the muscle spindle are the annulospira l endings which surro und the nonco ntrac tyle fibres of the musc le spindle.

Mot or End Plate It is the termi natio n of moto r fibres into skeletal muscles. As moto r nerve fib res reach the muscles, they lose their myelin Skelet al sheaths. Muscl e Fibre~ The neuro lemm a spread over the sarco lemm a and then disap pear. The termi nal part of the motor nerve fibres forms an expanded end called axonal bulb. The axonal bulb forms a depression on the sarco lemm a called Synaptic Moto r-End Plate gutte r. The space between the terminal part of the nerve fiber and the sarcolemma is called synap tic cleft. The synaptic cleft is rich in acetyl cholinesterase enzymes. The sarco lemm a under the axona l bulb is folded and is called junct ional folds. These folds are rich in acetylcholine recep tors. The axonal bulb is rich in mitoc hond ria, microtubules and synap tic vesicles. These vesicles are rich in acetylcholine. The sarcoplasm unde r the sarco lemm a is rich in mitoc hond ria and is called sole plate. -102...:.

Skin Functions: Protection, sweat excretion, heat regulation, reception of stimuli and formation of vitamin D. Structure: Formed of epidermis and dermis, the hypodermis is the subcutaneous fascia under the dermis. Types Of Skin: a) Thick non hairy skin as in palms and soles. b) Thin hairy skin covering the other body areas. Cornified Layer

'

Thick Non - : Hairy Skin

Lucidum Layer / . Granular ,/A Layer

The epidermis of thick skin is formed of the following 4 types of cells: 1. 2. 3. 4.

Keratinocytes. Melanocytes. Langerhan's Cells. Merkel's Cells

Prickle Cell Layer ,14--""B'BiJiil!l .. .;·.~

Malpighian Layer

... ·· · l Dermal Papilla

Tbick Non-Hairy Skin (Tip Of Finger) 1- Keratinocytes 1- Keratinocytes are formed of the foil owing 4 layers of cells a) Basal CeUs or Germinal Layer: It is formed of columnar cells attached to each other by junctional complexes. They have basophilic cytoplasm and basal oval nuclei. They can divide to replace the degenerated cells. b) The Prickle Cell Layer: It is formed of cuboidal cells joined with each other by desmosomes. They have basophilic cytoplasm rich in keratohyaline granules. - 103-

c) The Gnnular Cell layer: It is formed of flat cells rich in keratohyaline, phospholipids and mucopolysaccharide granules. These granules act as skin barrier. d) The Clear or Lucidum Cell Layer: It is formed of flat non-nucleated cells rich in eleidin granules. e) The Horny Layer: It is formed of layers of acidophilic horny scales called Squames rich in keratin material, they are continually shed off and replaced by new scales.

2- Melanocytes They are branched cells present between the basal cell layer of the epidermis. They can form melanin as they contain tyrosinase enzyme, therefore they give positive DOPA reaction.

3 - Langerhan's Cells They are branched cells present between the epidermal cells. They are phagocytic macrophage cells, they increase after skin injuries. -

Free Nerve Endings are present also between epidermal Cells.

4 - Merkel's Cells They are modified epidermal cells present between the basal cell layer, they act as receptor cells for touch sensation. Non myelinated sensory nerve fibres terminate under Merkel's cell by terminal disc.

The Dermis Of The Skin It consists of two layers: Papillary and Reticular Layers:

1. Papillary Layer Of.The Dermis It is formed of areolar connective tissue rich in blood capillaries. It contains touch receptors called Meissner's corpuscles. -104-

2. Reticular Layer Of The Dermis It is formed of a dense network of reticular and collagenous C. T. fibres. It has few blood capillaries and few connective tissue cells. It contains sweat glands and these receptors:

Pacinian corpuscles, Ruffini corpuscles and Krause ----end bulbs. N.B. The epidermis is fixed to the dermis by: 1. Hemi-desmosomes which fix the basal cells to the basement membrane. 2. The basement membrane fix the basal cells to the dermal connective tissue. 3. The dermal papillae fit into the concavities under the epidermis.

Tbe Hypodermis of the skin is formed of adipose connective tissue.

Sweat Glands Sweat glands are of 2 types; merocrine and apocrine : 1· Merocrine sweat glands are present all over the body except glans penis, and nail beds. - They are lined with clear ana dark cuboidal cells. - They secrete watery sweat through sweat secretory ducts which are lined with stratified cubical epithelium. 1- Apocrine Sweat glands are present in the axilla, pubic and perianal regions. - They are lined with clear and dark cuboidal cells. They secrete unpleasant viscous sweat which starts after puberty to give