1. Epithelial Tissue
Hazel Anne L. Tabo

2. General Functions
Epithelial (Gr. epi, upon, + thele, nipple) tissues are the covering and lining of surfaces (eg, skin, intestines),
Absorption - intestines
Secretion - glands
Sensation - gustative and olfactory neuroepithelium
Contractility - myoepithelial cells – breast
Regenerates quickly subjected to trauma & destruction.
Epithelial exposure to different matters:
Gases-integumentary & respiratory;
Liquids-circulatory & urinary;
Semisolids-GI tract

3. EPITHELIAL TISSUE Epithelium have 2 major categories: 1. Membranous e.
- located throughout the body, body covering, internal lining of cavities and lumina (hollow part of the tubes)
2. Glandular e.
- specialized tissues that form the secretory portion of glands

4. Tissue type
Cellular number
ECM
Nervous
Neuron – long intertwining axons
Absent
Epithelial
Abundant flat cells
Small amount
Muscle
Elongated myofibers
Moderate amount
Connective
Various wandering and fixed cells
Abundant

5. General features Derived from 3 germ layers: ectodermal-skin
mesodermal-inner lining of blood vessels
endodermal-inner lining of the GI tract)
Layer formed – either one (simple) or more (stratified) thick
Epithelial tissues are composed of closely aggregated polyhedral cells with limited ECM.
Epithelial cells are closely apposed to each other by adhesion molecules, membrane interdigitations, and intercellular junctions.
Intercellular connections – Influence the cells to form cellular sheets and form covering of body surfaces body and line internal cavities and glands are arranged as 3-D secretory units.

6. Basement membrane – underlying support where epithelial cells are rested. It demarcates the underlying CT from epithelium.
It is composed of:
Basal Lamina - Membrane proteins of the epithelial cells are anchored in the basal lamina.
The major 2 glycoproteins - LAMININ and Type IV COLLAGEN
FXN: acts as a selective, permeable filter between epithelium and connective tissue (CT).
Reticular Lamina - Reticular fibers embedded in ground substance that connect the basal lamina with the underlying CT. It is synthesized by cells of the CT.

8. LP
LP contain blood vessels, fibroblasts, etc.

9. General features
Generally avascular, nourishment through diffusion supplied by underlying CT (vascular).
Epithelial cells rest on connective tissue. The epithelia lining the cavity of internal organs of digestive, respiratory and urinary systems rests on Lamina propia (LP).

10. Squamous / Polyhedral
Flat, attached like tiles. Thinness allows rapid movement of substances through them.
Cuboidal
Cube / hexagon shaped. Important for secretion and some absorption.
Columnar Tall and cylindrical – protect underlying tissues.
For secretion and absorption.

11. Epithelial cells modifications:
Specialized apical surface-stereocilia, cilia & microvilli (surface area & absorption)
Specialization of lateral & basal cell surfaces: desmosomes –for adhesion in lateral cell membranes
zonula adherens or intermediate junctions - scattered around the epithelial cell
tight jxn. or zonula occludens supports the essential fxns. of epithelial tissues (strength; flexibility; endurance; regeneration).
Cellular Adhesion is due in part to the binding action of a family of transmembrane glycoproteins called cadherins. Cadherins lose their adhesive properties in the absence of Ca2+.

13. Types of cell junctions:
1. Tight junctions (occluding jxns.) – seal the intercellular spaces so that luminal contents cannot penetrate between the lining cells. “occlude” – to block / hinder
(ex: intestinal cells’ apex beneath the luminal surface of simple columnar epithelium) – Sealing strands (claudin)
2. Adhering jxns. – Zonula adherens, Desmosomes – macula adherens or spot adhering junctions (ex: Keratin in epithelium, epithelial tissue, cardiac & smooth muscles).
Hemidesmosome – half of the connexon (connexin) is attached to the basement membrane
3. Communicating jxns. – gap or nexus jxns, provide a conduit for passage of small molecules between adjacent cells. (ex:epithelium, cardiac & smooth muscles)

14. Specialization of cells:
Apical surfaces of epithelial cells:
Cilia – motile structures that contracts
Microvilli – supported by terminal web (microfilaments), that makes them contract and perform absorption.
Stereocilia – “not a cilia”; long microvilli but non-motile
Kartagener’s syndrome – inherited abnormality in cilia, compromising respiratory functions, with ineffective clearance of mucus.
Basal surface of cells – between epithelium and CT
Hemidesmosome – binds base of basal cells to the basement membrane

16. 1. Membranous epithelium Nomenclature
Simple epithelium Single layer of cells found in areas with activities such as diffusion, osmosis, filtration, secretion and absorption occur.
Stratified epithelium 2 < layers – protect underlying tissues in area of frequent exposure to environment.
Pseudostratified epithelium Looks like it, but it isn’t! Due to varying cell shapes and sizes. Lies only in single epithelium.

17. Naming Formula: Generally, If there are modifications present:
Number of cell layer + cell shape + epithelium
Ex: Simple cuboidal epithelium
If there are modifications present:
Number of cell layer + cell shape + modification + epithelium
Ex: Stratified squamous keratinized epithelium

18. Simple squamous epithelium
a single layer of flattened, scale- or plate-like cells; quite common in the body
The nuclei of the epithelial cells are often flattened or ovoid, i.e. egg-shaped, and they are located close to the center of the cells.
Organs: Heart, lymph vessels, capillaries, some serous membranes.
Fxn: Filtration, diffusion, osmosis and some secretion

19. Simple squamous epithelium
“Pavemented epithelium” – cells form continuous surface
Cell shape is similar to fish scales
Endothelium – epithelium of blood vessels
Mesothelium – epithelium of body cavity (peritoneal/abdominal cavity)

20. L – Mesothelium, serosal lining; R – Endothelium (arrows)

21. Simple squamous epithelium, Renal parenchyma

22. Simple cuboidal epithelium
Cells appear cuboidal / polygonal
Organ: Small excretory ducts of salivary and pancreas, the follicles of the thyroid gland, kidney tubules and on the surface of the ovaries.
Fxn: Secretion and absorption

24. L- Parotid gland, excretory duct (striated duct); R – Pancreatic duct (intercalated duct)

25. Simple columnar epithelium
Tall, pillar-like cells but slim. The nuclei of cells within the epithelium are usually located at the same height within the cells - often close to the base of the cells.
Modifications:
Non-ciliated type - 1 Layer of rectangular cells, often containing goblet cells; (+)microvilli
Organ: GI tract (stomach to anus), ducts of glands and gallbladder
Fxn: Secretion and Absorption
Ciliated type – (+)cilia
Organ: parts of upper resp. tract, uterine tubes, uterus, central canal of spinal cord
Fxn: Moves fluids / particles along passageways

26. Gall bladder
L & R – Non-ciliated type: Simple columnar non-ciliated epithelium or
Simple columnar with microvilli/brush border epithelium

27. Ciliated type: Simple columnar ciliated epithelium, Oviduct or Fallopian tube

28. Stratified squamous epithelium
Vary in thickness depending on the number of cell layers present; (+/-) keratin
Basal cell layer-the deepest Basal cells (cuboidal or columnar) are in contact with the basement membrane; mitotically active and replace the cells of the epithelium which are lost by "wear and tear".
Polyhedral cells – superior to basal cell layer
Flat/Squamous cells – at the surface of the epithelium (keratinized or non-keratinized)

29. Keratin layer Squamous cell layer Basal cell layer
Stratified squamous keratinized epithelium, Skin

30. Stratified squamous non-keratinized epithelium, Esophagus

31. Stratified cuboidal epithelium
2< layers of cuboid cells
Organs: Ducts of sweat glands, male urethra
Fxn: Protection
Stratified columnar epithelium
Many polyhedral cell layers – columnar cells in superficial layer
Organ:Lines part of urethra, excretory ducts of glands, anal mucous membrane
Fxn: Protection and Secretion

32. Stratified cuboidal epithelium,
L- excretory duct of sweat gland, R- excretory duct of salivary gland

33. Stratified columnar ciliated epithelium,
L- Mammary tissue (nipple) excretory duct, R – Parotid gland

34. Transitional epithelium
Variable appearance – cuboid to squamous
Organs: exclusively in excretory urinary passages (renal calyces and pelvis, ureter, urinary bladder, and part of the urethra).
Fxn: Permits distension
‘Relaxed‘ (contracted) state of the epithelium: it seems to be formed by many cell layers. The most basal cells have a cuboidal or columnar shape. Followed by several layers of polyhedral cells, and, finally, a layer of superficial cells, which have convex, Dome-shaped surface (Umbrella or dome-shaped cells).
‘Distended’ (stretched or uncontracted) state: epithelium resemble a stratified squamous epithelium.

35. Transitional epithelium (relaxed state)

36. Transitional epithelium (distended state), Urinary bladder
Note: The dome-shaped or “umbrella” cells appear to have a linear arrangement.  Flattened epithelium  Full bladder

37. Pseudostratified columnar epithelium
All cells attached to membrane, but not all reach surface; Nuclei of the epithelial cells are located in the widest part of the cell.
The nuclei of cells which do or do not reach the surface of the epithelium are often located at different heights within the epithelium giving a “stratified” appearance but only lies in a single layer.
Organs: Upper resp. tract; epididymis; male urethra
Fxn: Secretion and movement of mucus

38. Pseudostratified columnar ciliated epithelium, Trachea

39. Pseudostratified columnar non-ciliated epithelium, Ductus epididymis

40. Name the tissue:
An epithelium consists of single layer of cells with scale –like shaped cells.
Name: Simple squamous epithelium
An epithelium with double-layered cube-shaped cells.
Name: Stratified cuboidal epithelium