epethelial tissue and its introduction (1).pptx

Epethelial tissue its introduction and types and shapes

1. Epithelial Tissues

2. Introduction The epithelia are a diverse group of tissues that include both surface epithelia and solid organs . Surface epithelia cover or line all body surfaces, cavities and tubes and thus form the interfaces between different biological compartments

3. Functions: As such, epithelia mediate a wide range of activities such as : selective diffusion absorption secretion physical protection

4. Continue The majority of epithelial cells contain cytokeratin intermediate filaments, and this can be used to recognise an epithelial phenotype using immunohistochemistry , a technique often used in diagnostic histopathology to classify difficult malignant tumours .

5. Surface epithelia form continuous sheets comprising one or more layers of cells. Epithelial cells are bound to adjacent cells by a variety of membrane specialisations called cell junctions that provide physical strength and mediate exchange of information and metabolites

6. All epithelia are supported by a basement membrane of variable thickness. 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.

7. Thus epithelial cells are polarised with one side facing the basement membrane and underlying supporting tissues (the basal surface ) and the other facing outwards (the apical surface ).

8. Classifications Surface epithelia are traditionally classified according to 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 .

9. Epithelial tissue also classified according to shape Squamous epithelium  has cells that are wider than their height (flat and scale-like). Cuboidal epithelium  has cells whose height and width are approximately the same (cube shaped). Columnar epithelium  has cells taller than they are wide (column-shaped).

10. Khadar xalab(Dube) 12

11. Squamous Squamous cells have the appearance of thin, flat plates that can look polygonal when viewed from above.  Their name comes from  squāma , Latin for scale – as on fish or snake skin. The cells fit closely together in tissues; providing a smooth, low-friction surface over which fluids can move easily.

12. Squamous epitheliium is found lining surfaces such as the  skin , and  alveoli  in the  lung , enabling simple passive diffusion as also found in the  alveolar epithelium  in the lungs. Specialized squamous epithelium also forms the lining of cavities such as in blood vessels, as  endothelium  and in the  pericardium , as  mesothelium  and in other  body cavities

13. Cuboidal Cuboidal epithelial cells have a cube-like shape and appear square in cross-section. The cell nucleus is large, spherical and is in the centre of the cell. Cuboidal epithelium is commonly found in secretive tissue such as the  exocrine glands , or in absorptive tissue such as the pancreas, the lining of the kidney tubules as well as in the ducts of the glands

14. The  germinal epithelium  that covers the female  ovary , and the  germinal epithelium  that lines the walls of the seminferous tubules in the testes are also of the cuboidal type. Cuboidal cells provide protection and may be active in pumping material in or out of the lumen, or passive depending on their location and specialisation

15. Simple cuboidal epithelium commonly differentiates to form the secretory and duct portions of glands.  Stratified cuboidal epithelium protects areas such as the ducts of  sweat glands ,  mammary glands , and  salivary glands

16. Columnar Columnar epithelial cells are elongated and column-shaped and have a height of at least four times their width. Their nuclei are elongated and are usually located near the base of the cells. Columnar epithelium forms the lining of the stomach and intestines.

17. The cells here may possess  microvilli  for maximising the surface area for absorption and these microvilli may form a  brush border . Other cells may be  ciliated  to move mucus in the function of  mucociliary clearance .

18. Other ciliated cells are found in the  fallopian tubes , the uterus and  central canal  of the  spinal cord . Some columnar cells are specialized for sensory reception such as in the nose, ears and the  taste buds .  Hair cells  in the  inner ears  have  stereocilia  which are similar to microvilli .  Goblet cells  are modified columnar cells and are found between the columnar epithelial cells of the duodenum

19. They secrete mucus, which acts as a lubricant. Single-layered non-ciliated columnar epithelium tends to indicate an absorptive function ..

20. 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.

21. pseudostratified These are simple columnar epithelial cells whose nuclei appear at different heights, giving the misleading (hence "pseudo") impression that the epithelium is stratified when the cells are viewed in cross section.  

22. Ciliated   pseudostratified epithelial cells have cilia. Cilia are capable of energy dependent pulsatile beating in a certain direction through interaction of cytoskeletal microtubules and connecting structural proteins and enzymes

23. In the  respiratory tract   effect produced causes mucus secreted locally by the goblet cells (to lubricate and to trap pathogens and particles) to flow in that direction (typically out of the body).

24. Ciliated epithelium is found in the airways (nose, bronchi), but is also found in the uterus and  Fallopian tubes , where the cilia propel the ovum to the uterus.

25. Simple epithelia Simple epithelia are defined as surface epithelia consisting of a single layer of cells. Simple epithelia are almost always found at interfaces involved in selective diffusion, absorption and/or secretion.

26. Simple epithelia are almost always found at interfaces involved in selective diffusion, absorption and/or secretion. They provide little protection against mechanical abrasion and thus are not found on surfaces subject to such stresses.

27. In general, simple epithelial tissues are classified by the shape of their cells. The four major classes of simple epithelium are: ( 1) simple squamous (2) simple cuboidal (3) simple columnar (4) Psuedostratified columnar epitheilam

28. Stratified epithelium Stratified epithelium differs from simple epithelium in that it is multilayered. It is therefore found where body linings have to withstand mechanical or chemical insult such that layers can be abraded and lost without exposing subepithelial layers.

29. Cells flatten as the layers become more apical, though in their most basal layers the cells can be squamous, cuboidal or columnar .

30. Stratified squamous epithelium Stratified squamous epithelium consists of a variable number of cell layers that exhibit maturation from a cuboidal basal layer adherent to the underlying basement membrane to a flattened surface layer ..

31. Stratified squamous epithelium is well adapted to withstand abrasion since loss of surface cells does not compromise the underlying tissue; it is poorly adapted to withstand desiccation.

32. This type of epithelium lines the oral cavity, pharynx, oesophagus , anal canal, uterine cervix and vagina, sites which are subject to mechanical abrasion but which are kept moist by glandular secretions

33. Keratinising stratified squamous epithelium constitutes the epithelial surface of the skin (the epidermis ) and is adapted to withstand the constant abrasion and desiccation to which the body surface is exposed.

34. During maturation, the epithelial cells accumulate cross-linked cytokeratin intermediate filaments in a process called keratinisation resulting in the formation of a tough, non-living surface layer of squames consisting of the protein keratin K wrapped in residual plasma membrane .

35. Stratified cuboidal epithelium Stratified cuboidal epithelium is a thin, stratified epithelium that usually consists of only two or three layers of cuboidal cells. This type of epithelium is usually confined to the lining of the larger excretory ducts of exocrine glands such as the salivary glands.

36. Stratified cuboidal epithelium is probably not involved in significant absorptive or secretory activity but merely provides a more forceful lining than would be afforded by a simple epithelium .