Physiology 3120 Lecture Notes - Gastrin, Pylorus, G Cell

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Published on 26 Nov 2011
School
Western University
Department
Physiology
Course
Physiology 3120
Professor
Human Physiology
Monday, March 22, 2010
“Gastrointestinal II”
Stomach Secretion
Functionally different regions (look the same, but different functions)
Proximal part (2/3 of total volume) = oxyntic gland area
Has major exocrine secretory role (major product is HCl)
Secreted actively by H/K ATPase that pumps against a tremendous concentration
gradient (pH of plasma = 7; pH of stomach acid may be as low as 1) that is
1,000,000 to 1
The cell that produces HCl is called the oxyntic/parietal cell
Diffuse scattering of cells throughout mucosa (i.e. there isn’t a distinct gland)
Distal part (1/3 of total volume) = pyloric gland area
Small exocrine function, but its major function is endocrine; the hormone released is
gastrin (eventually released into vasculature)
Gastrin circulates in the blood and gets to the oxyntic cells; has a stimulatory effect on
HCl secretion
The cell that releases gastrin is called the G cell; also randomly distributed throughout
pyloric gland area
Regulation of acid secretion
Typically, acid secretion is broken down into 3 phases, divided based on where the stimulation is
at any point in time; food is the primary stimulation for any area of the GI tract
Not a sequential process; may have all 3 phases activated simultaneously
1. Cephalic phase
Refers to the brain
Any stimulation in the region of the brain stimulates GI tract
This occurs before food enters the stomach (can occur by sight, smell, thought, etc.)
Activate vagal nucleus; information is transported via the vagus nerve to the stomach;
vagus releases ACh, which has a stimulatory effect on oxyntic cells to increase acid
secretion
The vagal output activates both proximal and distal portion of the stomach; 2 stimulatory
agents then act on the oxyntic cells
ACh (directly from vagus)
Gastrin (vagus activates G cells, which release gastrin)
Have 2 different receptors for these agents; why would this happen?
oSynergism/potentiation: two distinct stimulators act on the same cell;
think of the analogy 1 + 1 = 100; having 2 stimulators acting on the same
cell amplifies the effect; therefore, it is a way of ensuring you get enough
acid; actually have a 3-way synergized response (see below)
ECL (enterochromaffin-like) cells (share some characteristics with mast cells) releases
histamine as well; histamine = potent activator of oxyntic cell; therefore, get a 3-way
synergized response; over-the-counter drugs that control acid block histamine
Under positive regulation by ACh and gastrin as well
**physiologically, it is impossible not to get the 3-way synergized response (it is all-or-none)**
Component Effect
ACh
Gastrin
Histamine
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Document Summary

Stomach secretion: functionally different regions (look the same, but different functions) Proximal part (2/3 of total volume) = oxyntic gland area. The cell that produces hcl is called the oxyntic/parietal cell: diffuse scattering of cells throughout mucosa (i. e. there isn"t a distinct gland) Distal part (1/3 of total volume) = pyloric gland area. Small exocrine function, but its major function is endocrine; the hormone released is gastrin (eventually released into vasculature) Gastrin circulates in the blood and gets to the oxyntic cells; has a stimulatory effect on. The cell that releases gastrin is called the g cell; also randomly distributed throughout. Hcl secretion: regulation of acid secretion pyloric gland area. Typically, acid secretion is broken down into 3 phases, divided based on where the stimulation is at any point in time; food is the primary stimulation for any area of the gi tract. Not a sequential process; may have all 3 phases activated simultaneously: cephalic phase.

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