Physiology 3120 Lecture Notes - Enteric Nervous System, Gastrin, Pylorus

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Published on 26 Nov 2011
Department
Professor
Human Physiology
Wednesday, March 24, 2010
“Gastro III”
Gastric Acid Secretion
2. Gastric phase
Occurs after food has entered the stomach and sits there
Perceptive input has been removed
2 ways to modulate acid secretion during this phase
a. Physical presence of the food mass, which causes mechanical stretching of the
stomach wall
oDistension of stomach increases acid secretion; put balloon in stomach and
inflate it increases acid
i. Primarily due to nervous reflexes; activate stretch receptors within muscle and mucosa that can activate a vagal
afferent-efferent reflex pathway; this releases ACh and gastrin; called the vago-vagal reflex
ii. Within the wall of the stomach, have enteric nervous system (cholinergic); it is a plexus (connects around the
entire gut) that receives information from stretch receptors; enteric nerves synapse on the oxyntic cells, and
receives information from stretch receptors
oThe enteric-mediated responses are inter-regional as well as intra-regional;
can stimulate in oxyntic area and get responses in oxyntic and pyloric
gland area
b. Chemical caused by some of the foodstuffs
oMost potent stimulus is protein or even small peptides; seems that the cells
respond directly to these compounds to activate secretion of their
compounds
3. Intestinal phase
Least important phase; contributes very little to the increase in acid secretion that results
from ingestion of a meal
Other Important Components of Gastric Exocrine Secretion
Pepsin
Secreted from oxyntic glandular mucosa, but not from the oxyntic cell; secreted by chief cell,
which secretes an inactive precursor called pepsinogen
Secretes inactive form because you don’t want pepsin breaking down the mucosal
proteins itself (i.e. auto-digestion)
Within the lumen, pepsinogen activated to pepsin by cleavage; acid catalyzes this
conversion
Chief cell under cholinergic control
ACh released due to food anticipation or presence
ACh thus stimulates the secretion of both HCl (from oxyntic cells) and
pepsinogen (from chief cells)
Within mucosa, there are chemoreceptors that detects H+ concentrations and release ACh
to activate the chief cells
Digests proteins by hydrolysis
Intrinsic factor (IF)
Mucoprotein secreted by oxyntic cell
Just a washout product of the oxyntic cell (i.e. anytime oxyntic cell secretes, IF secreted as well)
Binds vitamin B12 in stomach lumen because the only way to absorb that vitamin is if it is in
complex with IF; have uptake mechanism in ileum (distal portion of small intestine) that only
recognizes the IF-B12 complex
Required for RBC formation & maturation
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Document Summary

Occurs after food has entered the stomach and sits there. Least important phase; contributes very little to the increase in acid secretion that results from ingestion of a meal. Other important components of gastric exocrine secretion: pepsin. Secreted from oxyntic glandular mucosa, but not from the oxyntic cell; secreted by chief cell, which secretes an inactive precursor called pepsinogen. Secretes inactive form because you don"t want pepsin breaking down the mucosal. Within the lumen, pepsinogen activated to pepsin by cleavage; acid catalyzes this proteins itself (i. e. auto-digestion) conversion. Chief cell under cholinergic control: ach released due to food anticipation or presence, ach thus stimulates the secretion of both hcl (from oxyntic cells) and pepsinogen (from chief cells) Within mucosa, there are chemoreceptors that detects h+ concentrations and release ach to activate the chief cells. Just a washout product of the oxyntic cell (i. e. anytime oxyntic cell secretes, if secreted as well)

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