Basic Histology no.2 epithelium tissue.pptx

Histology of epithelial tissue

1. Epithelium Dr. S hiraz Yousif

2. Objectives At the end of this session you should be able to ; List the characteristic features of epithelium Interpret the function of epithelium Identify different types of epithelium

3. Tissue a group of similar cells specialized to carry on a particular function tissue = cells + extracellular matrix ECM is the nonliving portion of a tissue that supports cells 4 types epithelial = protection, secretion, absorption connective = support soft body parts and bind structures together muscle = movement nervous = conducts impulses used to help control and coordinate body activities

4. Epithelial Tissue epithelium covers surface of the body and lines its cavities.

5. The shape of the cells range from high columnar to cuboidal to low squamous cells.

6. Characteristic Features 1. composed of closely aggregated polyhedral cells with little extracellular substance. 2. Cells are arranged into sheets and have strong adhesion (they are marked in sites subjected to traction and pressure eg , in the skin).

7. Cont. 3. Has basement membrane anchors epithelium to underlying connective tissue The BM arranged in 2 layers : Dense layer(lamina densa ) Clear layer (lamina lucida ) BM is formed by glycogen fibrils and glycoproteins

8. Cont. 4. Polarity . 5. Lack blood vessels 6. Readily divide (ex. skin healing)

9. 7. apical cell surface specializations Microvillia (brush border) Cytoplasmic cell projections to increase the surface area e.g . intestine . Cilia elongated, highly motile structures it has coordinated movements to propel a current of fluid in one direction over (in the trachea ) Stereocilia long apical immotile processes of cells e.g. in the epididymis they increase the cells' surface area and facilitate the movement of molecules into and out of the cell

10. Intercellular adhesions and junctions

11. Tight junctions Seals to prevent the flow of materials between the cells( zonula occludens )   adhesive or anchoring junctions Sites of adhesion ( zonula adherens and desmosmes ) gap junctions   Channels for communication between adjacent cells .

12. Functions of the epithelial tissue

13.   Covering, lining, and protecting surfaces ( eg , skin ). Absorption ( eg , the intestines). Secretion ( eg , the epithelial cells of glands ). Contractility ( eg , myoepithelial cells).

14. Types of epithelial tissues

15. classified based on shape and number of cell layers shape squamous = thin, flat cells cuboidal = cube-shaped cells columnar = tall, elongated cells number simple = single layer stratified = 2 or more layers

16. To be continued…

17. Thank you …

18. Simple squamous a single layer of thin, flattened cells Function : Allows passage of materials by diffusion and filtration, facilitate movement and secretes lubricating substances Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels , and lymphatic vessels; lining of body cavity (serosae).

19. SIMPLE CUBOIDAL EPI. Single layer of cube like cells with large , spherical central nuclei. Function Secretion and absorption. Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface.

20. Simple columnar epi . Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus- secreting goblet cell Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus. location: Nonciliated type lines most of the digestive tract ,gallbladder, and excretory ducts of someglands ; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus.

21. Stratified epithelium

22. Stratified epithelia are classified according to the cell shape of the superficial layer(s): squamous, cuboidal, columnar, and transitional.

23. Stratified squamous epithelium composed of several layers , the basal cells are cuboidal or columnar, surface cells are flattened Can be keratinized in which the surface cells are full of keratin and dead, or non keratinized with a live cells. Function: protection. Location: skin epidermis (keratinized), mouth, upper esophagus, vagina(non keratinized).

24. Keratinized squamous epithelium

25. Transitional epithelium I s characterized by a superficial layer of domelike cells or squamous cells according to the degree of stretch of the bladder wall. location: lines only the urinary bladder, the ureter, and the upper part of the urethra . Function: protection and distensibilty .

26. Pseudostratified epithlium appear stratified because nuclei are at 2 or more levels NOT stratified because all cells touch basement membrane. they are ciliated and containing goblet cells. Function: protection, secretion, movement of mucus Location: linings of respiratory system

27. Any questions ?????