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Functions of epithelium
- Protection
- Absorption
- Secretion
- Sensation
- Contraction
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Characteristics of epithelium
- Avascular
- Cells are tightly packed
- All epithelium have a basal lamina
- Forms coverings / linings of organs
- Forms glands
- Characterized by intercellular junctions or specializations
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Protective epithelium are ______ where Absorptive epithelium are _________
- Stratified
- Simple (with high surface area)
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Components of Basal Lamina
- Type IV collagen
- Laminin
- Fibronectin
- Heperin Sulfate
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Epithelial Cell Apical Specializations
- Apical Domain:
- microvilli
- cilia
- stereocilia
- keratin
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Epithelial Cell Basal Specializations
Basal Domain:
hemidesmosomes - focal adhesions
- basement membrane
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Epithelial Cell Lateral Specializations
Lateral Domain: (CAM's)
- Zonula Occludens (tight junction)
- Zonula Adherens
- Macula Adherens (desmosomes)
- Gap Junctions
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Type VII Collagen
Anchoring fibrils of basal lamina
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Type III Collagen
Reticular fibers
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Type IV Collagen
Basal Lamina
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Desmosomes
(Macula Adherens)
"Spot weld" between epithelial cells
Associated with cytokeratin intermediate filaments
abundant in epithelia that are exposed to physical stress
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Hemidesmosome
Attaches cells to basement membrane
Prominent in epithelia exposed to physical forces
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Gap Junctions
(Nexus Junctions)
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
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Terminal Bar
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)
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Zonula Occludens
(Tight Junctions)
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.
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Zonula Adherens
Circles the entire cell.
Morphological similarities to the desmosome
Holds adjacent cells together.
Associated with actin microfilaments
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Focal Adhesions
Basal anchoring junction
Attaches cytoskeletal actin filaments to B.M.
Prominent role in migration of ep. cells (wound repair)
Mechanosensative to changes in ECM
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Microvilli
Specialized for absorption (kidney/small intestine)
Shorter than cilia
Core of actin microfilaments
Anchored to terminal web (microfilaments & intermediate filaments)
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Cilia
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
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Stereocilia
Sensory structure
Found in epididymis and inner ear
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Simple Squamous Epithelium
- Vascular system (endothelium)
- Body cavities (mesothelium)
- Bowman's Capsule (parietal layer - kidney)
- Respiratory spaces (lung)
- Endocardium
Exchange / Barrier (esp. CNS) / Lubrication
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Simple Cuboidal Epithelium
- Ducts / tubules of the kidneys
- Small ducts of exocrine glands
- Surface of ovaries (germinal epithelium)
- Thyroid follicles
Absorption / Secretion / Barrier / Conduit
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Simple Columnar Epithelium
- GI Tract!!!
- (small intestine, colon, stomach lining, gastric glands, gall bladder)
Absorption / Secretion
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Stratified Squamous Non-Keratinized Epithelium
- Esophagus
- Vagina
- Oral cavity
- Nasal cavity
Protection
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Stratified Squamous Keratinized Epithelium
Skin (epidermis)
Protection / Water proof
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Pseudostratified Epithelium
(Ciliated vs. Stereociliated)
- Cilia
- Trachea & Bronchal tree
- StereociliaMale reproductive tract (epididymis / ductus deferens)
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Transitional Epithelium
Urothelium!
- Renal calyces
- Ureters
- Bladder
- Urethra
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Types of Glands
- Endocrine
- Exocrine
- - holocrine
- - apocrine
- - merocrine (eccrine)
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Classification of multicellular glands
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Where are unicellular glands in the GI are first found?
GI Goblet cells in the duodenum
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What are crypts of Lieberkühn?
Simple tubular glands found in the colon
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What are the eccrine sweat glands of the skin? What is special about the ducts?
Simple coiled tubular glands. Ducts are stratified cuboidal epithelium
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Where are compound acinar glands found?
- Mucous secreting glands of the larynx
- Exocrine pancreas
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