Lecture 35 - Gastric physiology Flashcards
what are the 4 main functions of the stomach
- storage
- “grinding down” of food
- controlled delivery rate of food to the duodenum
- acid secretion and regulation
as food enters the stomach, the stomach relaxes in a process called ____
receptive relaxation/accomodation
give the function of the stomach product:
H+ ion
kills microbes, converts pepsinogen into pepsin and denatures protein
give the function of the stomach product:
pepsinogen
partial digestion of protein
give the function of the stomach product:
mucus
lubricates and protects mucosa
give the function of the stomach product:
bicarbonate
protects mucosa
give the function of the stomach product:
intrinsic factor
needed for normal absorption of B12
give the function of the stomach product:
water
dissolves and dilutes ingested material
give the function of the stomach product:
gastrin
stimulates acid secretion
regulates mucosal growth
stimulate pepsinogen secretion
give the function of the stomach product:
somatostatin
inhibits gastrin release
what is the “true stomach” in a ruminant? why is it called this?
abomasum; secretes HCl and other digestive enzymes
what is the cell type found lining the stomachs of ruminants, horses, and pigs
stratified squamous
absorptive epithelium contains ____ and _____
NaCl; SCFA
what are the 3 regions of mucosa in the stomach epithelium
- cardiac
- proper gastric
- antral/pyloric mucosa
describe the cardiac mucosa
cardiac glands secrete protective mucus and bicarbonate
describe proper gastric mucosa
contains parietal glands, chief cells, enterochromaffin-like cells, and D cells
describe antral/pyloric mucosa
contains D and G cells
match the cell type to its secretion
a. parietal cells
b. chief cells
c. enterochromaffin-like cells
d. D cells
e. G cells
- histamine
- pepsinogen
- gastrin
- somatostatin
- H+
a = 5
b = 2
c = 1
d = 4
e = 3
parietal cells are also called _____
oxyntic glands
describe the activation and action of:
parietal cells
produce HCl via a proton pump (activated by acetylcholine, histamine, and gastrin), creating an acidic environment to kill microbes
describe the activation and action of:
G cells
produce gastrin in response to stretching of stomach wall, higher gastric pH, protein in chyme
describe the activation and action of:
enterochromaffin cells
produce histamine in response to gastrin and pituitary peptides
the gastric proton pump is inhibited by what 3 things
- prostaglandins
- antihistamines
- somatostatin
what are the 3 main mediators of gastric acid secretion
- gastrin (acts on CCK and releases Ca2+)
- histamine (acts on H2 and releases cAMP)
- acetylcholine (acts on muscarinic cells and releases Ca2+)
describe gastric acid secretion in 5 steps
- gastric glands are stimulated and release H+ and Cl-
- H+ is secreted through a proton pump in exchange for 1 K+
- H+ ions come from the dissociation of intracellular carbonic acid
- as H+ is secreted, bicarbonate builds up in the cell
- exchanges Cl- into cell
gastrin release is stimulated by what 3 things
- gastric distension
- protein products in lumen of stomach
- vagal stimulation
acetylcholine comes from where
the vagus nerve
what 3 inputs stimulate the vagus nerve
- cephalic - sight, smell, physical presence of food
- gastric - distension and products in lumen of stomach
- intestinal - food in duodenum
what is the most important mediatory of acid secretion? why?
histamine
- ECL secretes it under most circumstances
- activates messenger that synergizes other secondary messengers
- H2 receptors are selectively expressed on parietal cells
summarize inhibition of gastric secretion in 2 steps
- stimuli that promote gastric secretion are not longer active
- at low intragastric pH, D cells secrete somatostatin which inhibits gastric release
the regulation of acid secretion is maintained by the relationship between
stomach volume, proton pump activity, and gastric acidity
high acidity means ___ pump activity and a[n] ____ stomach
low; empty
