1. Epithelial Tissues
م. م. فاطمة سوادي زغير

2. General Features: Minimum extracellular material.
Maximum cell-to-cell contact.
Minimum extracellular material.
Cell junctions: Several types of junctional specializations unite adjacent epithelial cells (tight junctions, desmosomes and gap junctions).
Supported by basement membrane (basal lamella).
Avascular: There are no blood vessels within the epithelial layer.
Derived from all embryonic germ layers, including endoderm, mesoderm and ectoderm

3. Classification of Epithelium
Number of layers of cells
Simple- one layer of cells. Each extends from basement membrane to the free surface
Stratified- more than one layer.
Pseudostratified- tissue appears to be stratified, but all cells contact basement membrane so it is in fact simple
Shape of cells
Squamous- flat, scale-like
Cuboidal- about equal in height and width
Columnar- taller than wide

4. Classifications of Epithelia

6. Simple squamous epithelium
a single layer of thin, flattened cells
look like a fried egg
easily damaged
common at sites of filtration, diffusion, osmosis; cover surfaces
air sacs of the lungs, walls of capillaries, linings of blood and lymph vessels

8. Simple Squamous Epithelium
Figure 4.3a

9. Simple cuboidal epithelium
single layer of cube-shaped cells
centrally located nucleus
secretion and absorption
surface of ovaries, linings of kidney tubules, and linings of ducts of certain glands

11. Simple Cuboidal Epithelium
Figure 4.3b

12. Simple columnar epithelium
single layer of cells that are longer than they are wide
nucleus located near basement mem.
ciliated or non ciliated
some have microvilli
goblet cells = secrete mucus
absorption, secretion, protection
linings of the uterus, stomach, and intestine

14. Simple Columnar Epithelium
Figure 4.3c

15. Pseudostratified columnar epithelium
appear stratified , nuclei are at 2 or more levels
NOT stratified b/c all cells touch basement membrane.
ciliated
goblet cells
protection, secretion, movement of mucus
linings of respiratory system

17. Pseudostratified Ciliated Columnar Epithelium
Figure 4.3d

18. Stratified Epithelia Contain two or more layers of cells
Regenerate from below
Major role is protection
Are named according to the shape of cells at apical layer

19. Stratified squamous epithelium
many layers of flattened cells
named based on appearance of top layer of cells
protection
outer layers of skin, linings of oral cavity, throat, vagina, and anal canal
Location
Keratinized – forms epidermis
Non-keratinized – forms lining of esophagus, mouth, and vagina

20. Stratified Squamous Epithelium
Specific types
Keratinized – contain the protective protein keratin
Surface cells are dead and full of keratin
Non-keratinized – forms moist lining of body openings

21. Stratified Squamous Epithelium
Figure 4.3e

23. Stratified cuboidal epithelium
2 or 3 layers of cuboidal cells
protection
linings of larger ducts of mammary glands, sweat glands, salivary glands, and pancreas

25. Stratified columnar epithelium
protection and secretion
vas deferens, part of the male urethra, parts of the pharynx (throat)

27. Transitional Epithelium
Figure 4.3h