BIOL 1840U Lecture Notes - Ribonuclease, Trypsin, Chymotrypsinogen

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29 Jan 2013
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GI Histology II: Glands of Digestion
I. Definitions
a. Intrinsic Glands—located in wall of GI tract
b. Extrinsic Glands—outside wall of GI tract: liver, pancreas, salivary glands
c. Types of Glands
i. Tubular exocrine gland—tubular secretory portion
ii. Alveolar or acinous gland—flask-like secretory portion
iii. Tubulo-alveolar gland—both tubular & flask-like
iv. Simple gland—duct doesn’t branch
v. Compound gland—duct branches
d. Serous—secretory products are proteins/ glycoproteins (eg: amylase, lipases, etc)
e. Mucous—secretory proteins are heavily glycoylated proteins (large)
II. Major Salivary Glands
a. Types
i. Parotid—contributes 25% saliva volume; serous; largest of the three
ii. Submandibular—contributes 70% saliva volume; mixed serous &
mucous
iii. Sublingual—contributes 5% saliva volume; mostly mucous; smallest
b. Function—microbial control, remineralization of teeth, digestion, lubrication,
mucosal production, pH maintenance, taste mediation
c. Components of Saliva—protein, glucose, urea, + some inorganic ions
d. Stimulation of secretion
i. ANS—sympathetic & parasympathetic stimulate secretion
(parasympathetic => largest increase in volume)
ii. Food in mouth—causes increase in salivary secretion
iii. Acid solutions—most potent salivation stimuli
e. Structure
i. Acini—secretory units composed of pyramidal secretory cells arranged in
spheres
1. mucous cells—basal compressed nucleus; apex granule-filled
2. serous cells—basal round nucleus; plentiful RER; protein-poor
granules in apex
3. may be purely mucous, purely serous, or mixed (Demilunes)
4. myoepithelial cells—flat, contractile cells which surround acini &
promote contraction/ excretion
ii. Ducts (parenchyma)
1. Intralobular
a. Intercalated—very small; low cuboidal cells
b. Striated—cuboidal or columnar cells w/ infolded basal
membranes & aligned mitochondria => striations
i. Striated ducts resorb Na & K (imperm to H2O) =>
final saliva is hypotonic (but w/ more K+)
2. Interlobular—simple columnar; VERY large & non-striated
3. Primary (excretory)—open into oral cavity; stratified squamous
iii. Connective Tissue (Stroma)—large vessels enter along major ducts
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