Epithelium

• Protection
• Absorption
• Secretion
• Sensation
• Contraction

• Avascular
• Cells are tightly packed
• All epithelium have a basal lamina
• Forms coverings / linings of organs
• Forms glands
• Characterized by intercellular junctions or specializations

• Stratified
• Simple (with high surface area)

• Type IV collagen
• Laminin
• Fibronectin
• Heperin Sulfate

• Apical Domain:
• microvilli
• cilia
• stereocilia
• keratin

Basal Domain:

• hemidesmosomes
• focal adhesions
• basement membrane

Lateral Domain: (CAM's)

• Zonula Occludens (tight junction)
• Zonula Adherens
• Macula Adherens (desmosomes)
• Gap Junctions

Anchoring fibrils of basal lamina

Reticular fibers

Basal Lamina

"Spot weld" between epithelial cells

Associated with cytokeratin intermediate filaments

abundant in epithelia that are exposed to physical stress

Attaches cells to basement membrane

Prominent in epithelia exposed to physical forces

Very close appositions of adjacent cellular membranes

Characterized by actual open channels (connexons) between cells.

Allow for rapid cell-to-cell communication (small molecules)

Common in cardiac m. and sometimes in nervous tissue

Band surrounding apical end of cell

Barrier to passage of material between cells

• Formed by:
• 1. Zonula Occludens (tight junction)
• 2. Zonula Adherens
• 3. Macula Adherens (desmosome)

Surrounds the cell like a belt or band.

Tight fusion of adjacent membranes

Prevents luminal materials from diffusing between adjacent cells

Membranes are fused into a pentalaminar (five-layered) structure.

Circles the entire cell.

Morphological similarities to the desmosome

Holds adjacent cells together.

Associated with actin microfilaments

Basal anchoring junction

Attaches cytoskeletal actin filaments to B.M.

Prominent role in migration of ep. cells (wound repair)

Mechanosensative to changes in ECM

Specialized for absorption (kidney/small intestine)

Shorter than cilia

Core of actin microfilaments

Anchored to terminal web (microfilaments & intermediate filaments)

Function is movement (respiratory tract)

Move together due to gap junctions

Organized cytoskeleton - nine doublets and central pair of microtubules

Microtubules anchored to basal bodies

Sensory structure

Found in epididymis and inner ear

• Vascular system (endothelium)
• Body cavities (mesothelium)
• Bowman's Capsule (parietal layer - kidney)
• Respiratory spaces (lung)
• Endocardium

Exchange / Barrier (esp. CNS) / Lubrication

• Ducts / tubules of the kidneys
• Small ducts of exocrine glands
• Surface of ovaries (germinal epithelium)
• Thyroid follicles

Absorption / Secretion / Barrier / Conduit

• GI Tract!!!
• (small intestine, colon, stomach lining, gastric glands, gall bladder)

Absorption / Secretion

• Esophagus
• Vagina
• Oral cavity
• Nasal cavity

Protection

Skin (epidermis)

Protection / Water proof

• Cilia
• Trachea & Bronchal tree

• Stereocilia
• Male reproductive tract (epididymis / ductus deferens)

Urothelium!

• Renal calyces
• Ureters
• Bladder
• Urethra

• Endocrine
• Exocrine
• - holocrine
• - apocrine
• - merocrine (eccrine)

GI Goblet cells in the duodenum

Simple tubular glands found in the colon

Simple coiled tubular glands. Ducts are stratified cuboidal epithelium

• Mucous secreting glands of the larynx
• Exocrine pancreas