Gastric Function Flashcards
what are the three main tasks of the stomach?
temporary food store (most important)
some degradation of protein and starch - smaller surface area
Hydrochloric acid kills bacteria in food - and enzyme (Pepsin) activation
most important stomach function?
temporary food store
band of muscle down the pipe of the oesophagus?
sphincter
what is almost absent in horses and really small in other species apart from pigs where it is large?
cardia
sphincters are?
muscular bands
when the stomach is empty, what is maintained?
contraction is maintained = tonic contraction
when an animal eats, what happens to the stomach?
the muscles relax = receptive relaxation
what is receptive relaxation regulated by?
via vagal fibres
what does relaxation allow for?
it allows for increase in stomach content without the increase in pressure - this aids the ‘food storage’ function of the stomach
what area of the stomach is the distal stomach referring to?
mainly to pyloric area
what does the arrival of waves of depolarisation result in?
large parts of the pylorus wall contracting simultaneously, increasing luminal pressure and forcing chyme through the partially open sphincter
type of epithelial on oesophageal sphincter?
stratified squamous
why does more active digestion occur in the distal stomach?
due to stronger peristaltic contractions
why are larger particles held back in the stomach?
so they can be broken down further
what are the 4 types of cells in the crypts/pits of the stomach?
mucin producing
parietal
chief
endocrine
what do the mucin producing cells secrete?
mucin
‘ogen’
inactive precursors
what do parietal cells secrete?
HCl and intrinsic factor
what do chief cells secrete?
pepsinogen
what do endocrine cells secrete?
G cells secrtee gastrin or ECL cells which secrtee histamine)
where is most gastric juice produced?
in the glands of fundus and corpus
what do the glands in the cardia region secrete?
only mucus - protective role
what do gastric juices consist mainly of?
HCl and pepsinogen
what mainly secretes HCl?
mainly from parietal cells
what does HCl do to tissue/muscle?
degrades connective tissue and muscle
what does HCl do to microorganisms?
kills them
carbonic anhydrase>?
enzyme for conversion of co2 and h2o to h2co3
after being fed, pH?
increases
pepsinogen stored and synthesised by?
chief cells
what is pepsinogen?
the inactive form of pepsin
what does pepsin do?
degrades feed proteins to peptides
type of catalysis that pepsinogen is used in?
autocatalysis role of pepsin
what three substances exert stimulatory effects in order to regulate gastric secretion?
ACh
gastrin
histamine
Where is HCl mainly secreted from?
mainly from parietal cells
for the regulation of gastric secretion, what three substances exert stimulatory effects?
ACh
Gastrin
Histamine
signals to nervous system good for?
stops overfeeding and over secretion
what happens during anticipatory part of secretion?
saliva and vagal nerve stimulation
summary of secretion:
saliva + vagal nerve stimu
vagal stimu of chief cells - pepsinogen
vagal stimulation of parietal cells - HCl
stimulation of G cells to release gastrin (+ve feedback on parietal cells and ECL cells)
ECL cell stimulation (histamine) drivers further HCl secretion
point of mechanoreceptors in stomach?
they detect the stomach wall stretching - drives secretion until feed is complete
how is secretion inhibited?
signals from duodenum
if pH falls too low - somatostatin release (blocks gastrin release)
At start of meal (b4 food reaches stomach) HCl secretion is low but H+ conc high
This blocks further acid secretion
When animal eats, stomach supplied with buffer (proteins) so [H+] decreased + gastrin is released
what happens when the animal is going to eat?
the stomach is supplied with buffer (proteins), [H+] decreases and gastrin is released
what happens if pH falls too low?
somatostatin release (blocks gastrin release)
level of HCl before food reaches the stomach (at the start of the meal)?
HCl secretion is low but [H+] is high
what does low HCl and high [H+] do?
it blocks further acid secretion
where is recently swallowed food found?
in the proximal area of the stomach
contraction in the proximal area of stomach - strength, meaning?
the contractions are weak so food layers in the order it was eaten - enables enzymes to act before becoming deactivated e.g. amylase for starch
describe the food found in the distal portion of the stomach?
it is well mixed with HCl and pepsin
gut’s own nervous system?
enteric nervous system
factors affecting gastric emptying?
expansion of the stomach wall
gastrin
Distension of duodenum
high fat and protein concentrations (requires slower digestion)
reduced pH
important mediators
what does GIP do?
mediates changes in gastric emptying
what does secretin do?
stimulated by acidity, increases HCO3 production by pancreas
what do the epithelial glands of the abomasum produce?
producing pepsinogen and HCl
what do young ruminants produce from the abomasum? what is this used for?
they also produce rennin
helps with digestion of milk
because the absomasum is not a storage organ - what does it do?
it receives a continuous flow of ruimen content
pH of the absomasum?
low pH
how is emptying regulated in the abomasum?
the same way as the stomach
what does HCl do for the stomach?
degrades connective tissue and muscle
and kills microorganisms
what does HCl do to pepsinogen?
it transforms pepsinogen (precursor) to pepsin (active enzyme)
How is HCl produced?
Produced by: H/K ATP-ase pump which provides the H+
and the HCO3-/Cl- pump which provides Cl-
How is HCl produced after a meal?
Production of HCl after a meal requires simultaneous stimulation of parietal cells by all three substances (ACh, gastrin, histamine)
Gastrin is released into the blood to stimulate secretion of HCl, pepsinogen and to promote gastric motility
Histamine acts as a paracrine hormone, stimulating HCl secretion
Vagal reflexed are stimulated by stomach expansion
