EPITHELIAL TISSUE (defn, classification & functions;PDF.pdf
- 1. TISSUE AND EPITHELIAL TISSUE BSC NURSINGI YR 2079/5/21 Dr. SK SAH ASSOCIATE PROFESSOR DEPT. OF ANATOMY
- 2. TISSUE • Tissue are a group of cells that have similar structure, origin and that function together as a unit. • A nonliving material, called the intercellular matrix, fills the spaces between the cells. • This may be abundant in some tissues and minimal in others. • The various types of tissue found in the human body are: 1. Epithelial tissue 2. Connective tissue 3. Muscular tissue and 4. Nervous tissue.
- 3. INTRODUCTION • The epithelia are a diverse group of tissues that covers the outer surface of the body or line the luminal surface of the structures and cavities of the body. • Features of Epithelial tissue: 1. Very cellular with little intercellular spaces. 2. Usually avascular. 3. Rests on the basement membrane. 4. Cells shows polarity. 5. Cells may display surface modifications. Basement membranes separate epithelia from underlying supporting tissues and are never penetrated by blood vessels; epithelia are thus critically dependent on the diffusion of oxygen and metabolites from adjacent supporting tissues.
- 5. CLASSIFICATION • Surface epithelia are traditionally classified according to three morphological characteristics: The number of cell layers: a single layer of epithelial cells is called simple epithelium, whereas epithelium composed of several layers is a stratified epithelium. • The shape of the component cells: this is based on the appearance in sections taken at right angles to the epithelial surface; cells are thus either squamous (flattened), cuboidal or columnar. In stratified epithelia the shape of the outermost layer of cells determines the descriptive classification. • The presence of surface specialisations such as cilia and keratin. For example the epithelial surface of the skin is classified as stratified squamous keratinising epithelium since it consists of many layers of cells, the surface cells of which are flattened (squamous) in shape, and it is covered by an outer layer of the proteinaceous material, keratin that is synthesised by the epithelial cells.
- 8. 1. SIMPLE SQUAMOUS • The cytoplasm of cells in this kind of epithelium forms only a thin layer. The nuclei produce bulgings of the cell surface . • In surface view the cells have polygonal outlines that interlock with those of adjoining cells. • Distribution: 1. lines the alveoli of the lungs. 2. lines the free surface of the serous pericardium, of the pleura, and of the peritoneum: here it is called mesothelium. 3. It lines the inside of the heart, where it is called endocardium;
- 9. 2. COLUMNAR EPITHELIUM • in vertical section the cells of this epithelium are rectangular. • In keeping with the elongated shape of the cells, the nuclei are also frequently elongated. • Can be classified as: a) In some situations the cell surface has no particular specialization: simple columnar epithelium. b) In some situations the cell surface bears cilia: ciliated columnar epithelium.
- 10. • Distribution/location: 1. Simple columnar (without cillia or microvilli)– mucus membrane of stomach and large intestine. 2. Simple columnar with striated border– in small intestine, with brush border in gall bladder. 3. Ciliated columnar epithelium– in respiratory tract, uterus, uterine tube, efferent ductules of testis, middle ear, auditory tube, ependyma lining the central canal of spinal cord and ventricles of brain.
- 11. 3. CUBOIDAL EPITHELIUM • Cuboidal epithelium is similar to columnar epithelium, but for the fact that the height of the cells is about the same as their width. The nuclei are usually rounded. • Distribution: 1.follicles of the thyroid gland, in the ducts of many glands, and on the surface of the ovary (where it is called germinal epithelium). 2.Choroid plexuses, the inner surface of the lens, and the pigment cell layer of the retina. 3.Cuboidal epithelium with a prominent brush border is seen in the proximal convoluted tubules of the kidneys.
- 12. 4. PSEUDO-STRATIFIED COLUMNAR EPITHELIUM • Sometimes, however, the nuclei appear to be arranged in two or more layers giving the impression that the epithelium is more than one cell thick. • Distribution: 1. some parts of the auditory tube, the ductus deferens, and the male urethra (membranous and penile parts). 2. ciliated pseudostratified columnar epithelium is seen in the trachea and in large bronchi.
- 13. 5.STRATIFIED SQUAMOUS EPITHELIUM • This type of epithelium is made up of several layers of cells. • The cells of the deepest (or basal) layer rest on the basement membrane: they are usually columnar in shape. Lying over the columnar cells there are polyhedral or cuboidal cells. As we pass towards the surface of the epithelium these cells become progressively more flat, so that the most superficial cells consist of flattened squamous cells. • Stratified squamous epithelium can be divided into two types: non-keratinised and keratinised.
- 14. • Stratified squamous epithelium (both keratinised and non-keratinised) is found over those surfaces of the body that are subject to friction. • As a result of friction the most superficial layers are constantly being removed and are replaced by proliferation of cells from the basal (or germinal) layer. This layer, therefore, shows frequent mitoses. • Distribution: 1. Keratinised stratified squamous epithelium covers the skin of the whole of the body and forms the epidermis. 2. Non-keratinised stratified squamous epithelium is seen lining the mouth, the tongue, the pharynx, the oesophagus, the vagina and the cornea. Under pathological conditions the epithelium in any of these situations may become keratinised.
- 15. 6. TRANSITIONAL EPITHELIUM • Multi-layered epithelium and is 4 to 6 cells thick. • It differs from stratified squamous epithelium in that the cells at the surface are not squamous. The deepest cells are columnar or cuboidal. The middle layers are made up of polyhedral or pear- shaped cells. The cells of the surface layer are large and often shaped like an umbrella. • Transitional epithelium is found in the renal pelvis and calyces, the ureter, the urinary bladder, and part of the urethra. Because of this distribution it is also called urothelium.
- 16. PROJECTIONS FROM THE CELL SURFACE • Cilia • Microvilli • Stereocilia
- 17. Differences b/w Cilia and Microvilli Cilia Microvilli 10µm in length and 0.25µm in diameter. 1-2mm in length and 75-90µm in diameter. Motile Non-motile Contains 9+2 pattern of microtubules. Contain numerous microfilaments. Concerned with movement of ova through uterine tube and movement in trachea and bronchi towards pharynx. Concerned with absorptive functions. Seen over lining epithelium of respiratory tract and uterine tube. Seen over the intestinal epithelium.
- 18. GLANDULAR TISSUE • Glands (gland cells) are derived from epithelial tissue which helps in secretion. • The glands develop as cords of epithelial cell from the surface membrane and invade the adjoining connective tissues. • The glands are classified as: 1. Exocrine glands– secretes out of the body by the ducts. 2. Endocrine glands– secretes within the substance of the body, directly into the capillaries and require no ducts, hence called ductless gland.
- 19. Gland Categories 1) Exocrine - glands that exude secretions into a ductule system. Have two parts, acinous = secretory bulb and ductule. 2) Endocrine - glands exuding secretions directly into body fluids, ultimately blood. 3) Mixed - glands combining both the above characteristics (e.g. liver) in the same cell. 4) Paracrine - tissue secretions affecting own cells.
- 21. Thin watery Thick viscous Zymogen granules Mucigen droplets Round central nucleus Flat peripheral nucleus Parotid gland Sublingual gland Serous Mucous
- 22. Classification Glands EXOCRINE GLAND ENDOCRINE GLAND Unicellular Multicellular Cord & Clump type Follicular type A/C TO SHAPE OF GLANDS A/C TO THE DUCTS BRANCHED OR UNBRANCHED A/C TO MANNER OF SECRETION A/C TO DEVELOPMENT Tubular Alveolar Tubulo- alveolar Simple Compound Holocrine Apocrine Merocrine Ectodermal Mesodermal Endodermal
- 23. EXOCRINE GLANDS • May be Unicellular and Multicellular. Unicellular glands: --e.g; Goblet cells. Multicellular glands: classified as; 1. A/C TO SHAPE: Tubular, Alveolar, Tubulo- Alveolar. 2. A/C TO BRANCHING: Simple and Compound. 3. **A/C TO MANNER OF SECRETION: 4. A/C TO DEVELOPMENT.:
- 25. **According to manner of secretion 1. Holocrine: The cells disintegrates and die to liberate the secretion. It is a destructive process. E.g Sebaceous gland. 2. Apocrine: here the luminal part of the cell disintegrates, leaving the nucleus and the basal portion. E.g. Mammary gland. 3. Merocrine: here the secretion is discharged through the intact cell membrane without destruction of the cell. E.g. most of the glands of the body. 4. Cytocrine: cells released as secretion. Eg; sperm from testis.
- 26. ACCORDING TO THE DEVELOPMENT 1. ECTODERMAL: Glands of the skin, mammary gland, lacrimal and salivary gland. 2. MESODERMAL: Suprarenal cortex, gonads, kidneys, spleen, etc. 3. ENDODERMAL: thymus, pancreas, liver, lining cells of glands of alimentary tracts, prostate, urethral glands, etc.
- 27. ENDOCRINE GLANDS • These are the ductless glands and secrets various hormones and chemical substances into the blood capillaries. • The gland is of two type: 1. Cord and clump type: (most of the endocrine glands of the body). 2. Follicular type: e.g. Thyroid follicles.
- 28. • Epithelial tissue gives origin to benign (Papilloma) and malignant (Carcinoma) tumors. • Malignant tumors from glandular tissue- Adenocarcinoma. Clinical Importance
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