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Functions of epithelium
Characteristics of epithelium
- Cells are tightly packed
- All epithelium have a basal lamina
- Forms coverings / linings of organs
- Forms glands
- Characterized by intercellular junctions or specializations
Protective epithelium are ______ where Absorptive epithelium are _________
- Simple (with high surface area)
Components of Basal Lamina
- Type IV collagen
- Heperin Sulfate
Epithelial Cell Apical Specializations
- Apical Domain:
Epithelial Cell Basal Specializations
- focal adhesions
- basement membrane
Epithelial Cell Lateral Specializations
- Zonula Occludens (tight junction)
- Zonula Adherens
- Macula Adherens (desmosomes)
- Gap Junctions
Type VII Collagen
Anchoring fibrils of basal lamina
Type III Collagen
Type IV Collagen
"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
Found in epididymis and inner ear
Simple Squamous Epithelium
- Vascular system (endothelium)
- Body cavities (mesothelium)
- Bowman's Capsule (parietal layer - kidney)
- Respiratory spaces (lung)
Exchange / Barrier (esp. CNS) / Lubrication
Simple Cuboidal Epithelium
- Ducts / tubules of the kidneys
- Small ducts of exocrine glands
- Surface of ovaries (germinal epithelium)
- Thyroid follicles
Absorption / Secretion / Barrier / Conduit
Simple Columnar Epithelium
- GI Tract!!!
- (small intestine, colon, stomach lining, gastric glands, gall bladder)
Absorption / Secretion
Stratified Squamous Non-Keratinized Epithelium
- Oral cavity
- Nasal cavity
Stratified Squamous Keratinized Epithelium
Protection / Water proof
(Ciliated vs. Stereociliated)
- Trachea & Bronchal tree
- StereociliaMale reproductive tract (epididymis / ductus deferens)
- Renal calyces
Types of Glands
- - holocrine
- - apocrine
- - merocrine (eccrine)
Classification of multicellular glands
Where are unicellular glands in the GI are first found?
GI Goblet cells in the duodenum
What are crypts of Lieberkühn?
Simple tubular glands found in the colon
What are the eccrine sweat glands of the skin? What is special about the ducts?
Simple coiled tubular glands. Ducts are stratified cuboidal epithelium
Where are compound acinar glands found?
- Mucous secreting glands of the larynx
- Exocrine pancreas
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