1. Epithelium
Khaleel Alyahya
Monday March 22, 2009

2. Tissue There are only 4 basic types of tissues 1. Epithelial tissue
2.   Connective tissue
3.   Muscular tissue
4.   Nervous tissue

3. Epithelium
is a tissue composed of cells that line the cavities and surfaces of structures throughout the body

4. Special Features of Epithelium
Epithelial cells are closely packed cells, and form continuous sheets.
Adjacent cells are bound together by cell junctions.
They have one free surface (apical).

5. Special Features of Epithelium
The lower surface of all types of epithelia rest on Basement membrane /Basal lamina, a structureless material secreted by the cells.
Epithelial tissues are avascular (no direct blood supply). Nutrition depends on diffusion from underlying connective tissue.
Epithelial cells can regenerate easily.

6. Functions of Epithelium
Protection
Absorption
Secretion
Exchange of gases, nutrients, & waste products

7. Classification of Epithelia
The epithelium is classified according to:
1) the number of layers.
2) the shape of the outermost layer.

8. The first & second names are combined to describe the epithelium fully.
Stratified epithelia are described according to the shape of their superficial cells.
Thus, depending on the number of cell layers, the epithelia is divided into:
I.    Simple Epithelium
Consisting of a single layer of cells
II.    Stratified Epithelium
Consisting of two or more layers of cells

9. Simple Epithelia:
1) Simple Squamous Epithelium
Composed of a single layer of flattened cells.
The term ‘Squamous’ is derived from the comparison of the cells to the scales of a fish.
Examples:
Blood capillaries
Pulmonary alveoli

10. Simple squamous epithelium

11. Consists of a single layer of square shaped cells
2) Simple Cuboidal Epithelium
Consists of a single layer of square shaped cells
Centrally placed nucleus
Examples:
Kidney tubules
Thyroid gland
Surface of ovaries
Simple Epithelia:

12. Kidney tubule
Thyroid gland

13. 3) Simple Columnar Epithelium
Simple Epithelia:
3) Simple Columnar Epithelium
Single layer of tall column-like cells
Goblet cells (mucus producing cells) may be seen in this type of epithelium
Its has ovoid nuclei located in basal half of the cells
Examples:
Stomach and intestines

15. Simple Epithelia:
4) Pseudostratified Columnar Epithelium
Single layer of cells but gives false impression of more than one layer of cells. (stratified)
There are tall cells which reach the surface and shorter ones that don’t
All cells rest on the same basement membrane
The nuclei show different levels of height
The higher cells may be ciliated.
Goblet cells are seen in respiratory epithelium
Example:
Trachea

17. Pseudostratified Columnar Epithelium

18. Stratified Epithelia:
Consists of two or more cell layers
Their main function is protection.

19. Stratified Epithelia:
1) Stratified Squamous Epithelium
Stacked epithelial cells with the surface cells being flat
The cells at the base are cuboidal or columnar
The basal and intermediate cells maintain the ability to divide
Cells at the surface are dead and lack nuclei

20. Stratified squamous ( Non-keratinized) epithelium
Is formed of several layers of cells
The most basal layer rests on basal lamina and it is cuboidal cells
The most superficial layer is formed of flat squamous cells not covered with keratin
Example: lining of mouth, oral pharynx, esophagus, true vocal cords and vagina)

21. Stratified Squamous ( Non-keratinized) Epithelium

22. Stratified Squamous Epithelium (Non-keratinized)

23. Stratified Squamous Epithelium (Non-keratinized)

24. Stratified squamous (Keratinized) epithelium
similar to non keratinized type but the superficial layer is covered with keratin
Example: epidermis of skin

25. Stratified Epithelia:
2) Stratified Cuboidal & Columnar Epithelium
Usually have two cell layers with surface cells cuboidal or columnar
The basal cells vary in size & shape
Examples:
Ducts of the large exocrine glands such as salivary glands (columnar), sweat glands (cuboidal).

26. Stratified Cuboidal

27. Stratified Epithelia:
3)Transitional Epithelium:
Is a modified type of ‘Stratified Squamous epithelium
It is present in the urinary system organs
In the relaxed state, it shows 5-8 layers
Basal cells are cuboidal or columnar and surface cells are rounded
When the epithelium is stretched, it appears 2-3 layers thick and the surface cells appear flattened
Example:
Urinary bladder
Ureters

28. Transitional Epithelium (relaxed)

29. Transitional Epithelium ( full)

30. summary Simple Epithelium Simple Squamous Epithelium
Simple Cuboidal Epithelium
Simple Columnar Epithelium
Pseudostratified Columnar Epithelium
Stratified Epithelium
Stratified Squamous Epithelium
Non-keratinized
Keratinized
Stratified Cuboidal Epithelium
Stratified Columnar Epithelium
Transitional Epithelium

32. Glandular Epithelium:
The gland consists of one cell (unicellular gland like Goblet cells), or more than one cell (multicellular gland like pancreas & salivary glands)
Classification of glands:
1) Exocrine Glands:
They retain their ducts and secrete their product through them, e.g. pancreas & salivary glands.
2) Endocrine Glands:
They lose their ducts and secrete their products directly into the blood, e.g. pituitary & thyroid glands.

33. That’s all folks!
Questions?