GIT physiology 2 Flashcards
4 regions of the stomach
cardia, fundus, corpus (body), antrum
pepsinogen
inactivated pepsin (so it doesn’t digest the secreting cell)
3 types of exocrine gland cells in the stomach
mucous neck cells - mucus
parietal cells - intrinsic factor and HCL
chief cells - pepsinogen and gastric lipase
2 types of endocrine cells in the stomach
G cell - secretes gastrin
D cell - secretes somatostatin
the body is
a reservoir
the antrum is
a mixer
receptive relaxation
sago-vagal response
relaxes the stomach
triggered by stretch of bolus of food
allows stomach to expand
mixing and grinding
closure of the pyloric sphincter
rhythmic waves of muscular activity
duodenal distension causes
CCK/secretin secretion
causes the stomach to relax to prevent overloading of the duodenum
pyloric sphincter contracts to prevent regurgitation
what controls gastric emptying
feedback from the duodenum
acidity, fat, amino acids, hypertonicity, distension
vomiting is stimulated by
irritation
balance
limbic system - emotional
blood chemical
mucous neck cells secrete
mucus and bicarbonate
mucus secreted in response to
tonic secretion (constant) and irritation of mucosa
bicarbonate is for
neutralisation - trapped in the mucosa
purpose of mucus
physical barrier between the lumen and the epithelium
purpose of bicarbonate
buffers gastric acid to prevent damage to epithelium
parietal cells secrete
gastric acid and intrinsic factor
gastric acid and intrinsic factor are secreted in response to
acetyl choline, gastrin, histamine
purpose of gastric acid
activates pepsin, kills bacteria
purpose of intrinsic factor
complexes with vitamin B12 to permit absorption
enterochromaffin-like cell secretes
histamine
histamine is secreted in response to
acetylcholine, gastrin
purpose of histamine
stimulates gastric acid secretion
chief cells produce
pepsinogen, gastric lipase
pepsin and gastric lipase are secreted in response to
acetylcholine, acid, secretin
purpose of pepsin(ogen)
digests proteins
purpose of gastric lipase
digests fats
D cells secrete
somatostatin
somatostatin is secreted in response to
acid in the stomach
purpose of somatostatin
inhibits gastric acid secretion
G cells secrete
gastrin
gastrin secreted in response to
acetylcholine, peptides and amino acids
purpose of gastrin
stimulates gastric acid secretion
gastric mucosa surface
secretes mucus and HCO3- (acid protection)
oxyntic gland area
acid producing
body and fundus (proximal 80%)
secretes HCl, pepsinogen, IF, mucus
pyloric gland area
antrum (distal 20%)
produces mucus
secrets gastrin (G and D cells)
mechanism for acid secretion
maximal in gastric secretions
proton pump which actively transports H+ out in exchange for K+ in
proton pumps are located
in the canalicular membrane of the secreting cell, in vessicles in quiescent cell
hydrochloric acid produced from
CO2 in the blood being made into carbonic acid
for every mole of hydrochloric acid produced
one mole of bicarbonate is produced
when inactive proton pumps are
stored in vessicles so they can’t be activated
to activate proton pumps
vessicles containing them are exocytosed
3 hormones activated exocytosing of proton pump containing vesicles
acetylcholine, histamine, gastrin
stimulants of gastrin release from G cells
vagal stimulation
small proteins and protein digestion products
antral distension
gastrin release is inhibited by
acid
somatostatin
blood borne - secretin, GIP, VIP, glucagon, calcitonin
roles of gastrin
stimulate acid from parietal cells
release histamine from ECL cells
release pepsinogen from chief cells
D cells
when stomach pH is too low secrete somatostatin to stop gastrin production to stop acid production
pH sensitive
parietal cells produce
acid
mucus gel contains
muffins (glycoproteins) plus trefoil factor (peptides) which stabilise the mucous layer