BIOL 1840U Lecture Notes - Aldosterone, Endocrine System, Active Transport

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29 Jan 2013
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Overview Of GI Physiology
I. Introduction
a. Gastrointestinal System—GI tract, gall bladder, liver, pancreas
b. Function—transform (digest) large things into their absorbable components
II. Comparison With Nephron
a. Both tubes are lined w/ an absorptive epithelium
b. Dependent on Na-coupled mechanisms
c. Use leaky & tight jxns to support bulk flow
III. Mechanisms for Na reabsorption
a. Na/solute cotransport across basal membrane
b. Na/K exchange (Na absorption w/ K secretion; requires 1 ATP) per cycle
c. Na/H & Cl/HCO3 exchange (=> net excretion of HCl)
d. Aldosterone increases Na reabsorption & K secretion (as in kidney)
IV. Enteric Nervous System (ENS)
a. Second integrator of GI function (along with endocrine system)
b. 3 hard-wired programs
i. Fed motor pattern—mixture of segmental & propagated contractions
ii. Fasting motor pattern—migrating myogenic complex (MMC), repeats
x90 min, fxn is to remove residual gut contents periodically
iii. Ileus—a relaxive reflex
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