1. Epithelium (epithelial tissue) Dr. Abdullah Aldahmash

2. Epithelium Epithelial cells are closely packed cells, and form continuous sheets. Epithelial cells are closely packed cells, and form continuous sheets. Function Function 1. Protaction 2. Transcellular transport 3. Secretion 4. Absorption 5. Detection of sensations

3. Special Characteristics of Epithelium Adjacent cells are bound together by cell junctions. The lower surface of all types of epithelia rest on Basement membrane / Basal lamina, a structureless material secreted by the cells.

4. Special Characteristics of Epithelium Epithelial tissues are avascular (no direct blood supply). Nutrition depends on diffusion from underlying connective tissue. Epithelial cells regenerate easily.

5. Classification of Epithelia: Epithelium is divided into two types: 1. Covering & Lining Epithelia. 2. Glandular Epithelia.

6. Basement Membrane Noncellular layer that secures the overlying tissues Most epithelial tissues have a basement membrane

7. Epithelial Tissue Classifications Epithelial tissue is classified according to the number of cell layers and the shape of each epithelial cell

8. Epithelial Tissue Classifications Simple epithelium A single layer of cells Stratified epithelium More than one layer of cells

9. Epithelial Tissue Classifications Pseudostratified epithelium Contains a single layer of cells of varying heights All cells attach to the basement membrane, but some fail to reach the free surface, giving the appearance of multiple layers Transitional epithelium Consists of layers of stratified cells that change shape from cuboidal to squamous when the organ is stretched

10. Epithelial Tissue Classifications Shape of each epithelia Squamous Flat sheets Cuboidal Rows of square-shaped cells Columnar Rows of tall, thin cells

11. Epithelia are derived from the three embryonic germ layers Ectoderm: epidermis and glands of skin, cornea, oral and nasal mucosae. Endoderm: liver, pancreas, lining of the GI and respiratory. Mesoderm: uriniferous tubules of kidney, lining of male and female reproductive system, endothelial lining of circulatory system.

13. Simple Epithelia

14. 1) Simple Squamous Epithelium: Composed of a single layer of flattened cells. The term ‘ squamous ’ derives from the comparison of the cells to the scales of a fish.

15. Simple Epithelia 2) Simple Cuboidal Epithelium: 2) Simple Cuboidal Epithelium: · Consists of a single layer of square shaped cells (2D). · Centrally placed nucleus. Example: Kidney tubules.

17. 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. Examples: Stomach and intestines.

19. 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 that reach the surface with other shorter ones that don ’ t.

20. Simple Epithelia 4) Pseudostratified Columnar Epithelium 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. Examples:Trachea

22. Stratified Epithelia

23. Stratified epithelia are described according to the shape of their superficial cells. Consists of two or more cell layers.. Their main function is protection.

24. Stacked epithelial cells with the surface cells being flat. The cells at the base are cuboidal or columnar. The intermediate cells are polygonal. The basal and intermediate cells maintain the ability to divide. Cells at the surface are dead and lack nuclei. 1) Stratified Squamous Epithelium (Keratinized & nonkeratinized)

27. Usually have two cell layers with surface cells cuboidal or columnar. 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). 2) Stratified Cuboidal & Columnar Epithelium:

28. 3) Transitional Epithelium: Is a modified type of Stratified Squamous epithelium. Present in the urinary system organs. In the relaxed state, it shows 5-8 layers.

29. 3) Transitional Epithelium: Basal cells are cuboidal or columnar, intermediate cells are polygonal, and surface cells are rounded. When the epithelium is stretched, it appears 2-3 layers thick and the surface cells appear flattened.

32. Junctional complexes Occluding junctions (tight junction) Anchoring junctions Communicating junction

33. Renewal of epithelial cells Skin 28 days Small intestine 4-6 days Others renewed periodically until adulthood

34. Glands

35. Development Paranchyma = glandular epithelia Stroma = connective tissue

36. Product of epithelial glands Apolypeptide hormones e.g. from pitutary gland A waxy substance e.g. ear canal gland Mucinogen e.g. goblet cells Milke (protein, lipid and carbohydrates)

37. Classifications of epithelial glands 1- Exocrine secrete via ducts 2- Endocrine (Ductless) secrete into blood or lymphatic vessels Cytokines and their effects Autocrine, paracrine and endocrine Results: Constitutive secretory pathway Regulated secretory pathway

38. Exocrine - Most commonly found in digestive, respiratory and urogenetal - can be Unicellular or multicellular - secrete: mucous (e.g. salivary gland), serous (e.g pancreas) or mix (submandibular) - there are three mechanisms by which they release secretion: merocrine (via exocytosis), apocrine (!!) or holocrine (secretory cells die and become product)

39. Exocrine: mechanism of secretion - there are three mechanisms by which they release secretion: - merocrine (via exocytosis), - apocrine (!!) - or holocrine (secretory cells die and become product)

40. Classifications of Exocrine glands 1-Unicellular e.g. goblet cells 2-Multicellular classified into: simple (ducts do not branch) compound (ducts do branch- septa) further into: tubular, acinar (alveolar)or tubuloalveolar