Physiology and Pharmacology of Gastric Secretion Flashcards
what is the volume range of the stomach?
50-1000ml depending on whether recently ate or not
how does the stomach expand and relax without changing tension on the walls?
ruggae (folds) allow it to expand receptive relaxation (driven by vagus) to accommodate food from oesophagus
what are the 2 functional areas of the stomach?
body/fundus = storage antrum = grinding
how is the chyme mixed in the stomach?
churning action of gastric smooth muscle (peristalsis) pushes chyme against closed pyloric sphincter which forces it back (retropulsion) mixing it around
what determines escape of chyme through the intermittently opened pyloric sphincter?
strength of antral wave (peristalsis) which is governed by gastric and duodenal factors
what gastric factors increase the rate of emptying of chyme in the stomach?
volume of chyme in stomach
distension (increases emptying due to stretching smooth muscle, stimulates intrinsic nerve plexuses, increases vagus nerve activity - vagal bagal reflex)
consistency of chyme (thinner = faster emptying)
what duodenal factors influence the rate of emptying of chyme in the stomach?
neuronal (signals from enteric nervous system decrease antral wave activity) hormonal responses ( release of enterogastrones from duodenum inhibits stomach contraction via activation of endocrine cells producing secretin and CKK)
what 4 stimuli in the duodenum drive the neuronal and hormonal response?
1) fat (delays emptying)
2) acid (delays emptying)
3) Hypertonicity (delays emptying)
4) distension
what are the 2 divisions of the gastric pit which descends through sunmucosa into the lamina propria?
pyloric gland area
oxyntic mucosa
what is produced in the pyloric gland area of the gastric pit?
D cells release somatostatin
G cells release gastrin
what is produced in the oxyntic mucosa of the gastric pit?
chief cells release pepsinogen
parietal cells release HCl, intrinsic factor and gastroferrin
Endochromaffin like cells secrete histamine
what is the function of HCl?
activates pepsinogen into pepsin
denatures protein
kills most micro-organisms ingested with food
what is the function of pepsinogen?
inactive precursor of pepsin
pepsin, once formed, is autocatalytic so can convert more pepsinogen to pepsin
what is the function of intrinsic factor and gastroferrin?
absorption of B12 and iron respectively in duodenum
what is the function of histamine?
stimulates HCl secretion
