physiology of the stomach 1 Flashcards
what are the functions of the stomach
- temp storage of food
- mechanical digestion by stomach movements
- chem digestion of proteins
- regulation of passage of chyme into small intestine
- secretion of intrinsic factor, essential for absorption of vitB12
how does mechanical digestion in the stomach work
the muscularis enables food to be churned - particularly in the antrum where the muscle wall is thicker
food mixed with gastric juice to produce chyme, chyme passes through pyloric sphincter to duodenum
what are the three types of cells that together produce gastric juices
- zymogenic (chief/peptic) cells
- parietal (oxyntic) cells
- goblet (neck) cells
what are additional cells in gastric glands
- G cells
- Enterochromaffin (mast like) cells
- D cells
what do G cells do
secrete gastrin
what do enterochromaffic (mast like) cells do
secrete histamine
what do D cells do
secrete somatostatin
are there parietal cells in the antrum
no
what happens during chemical digestion in the stomach
- proteins are broken down by pepsin
- gastric lipase breaks down fat at a higher pH
where is pepsin active
only active in acid environment
how is pepsin produced
its converted from pepsinogen by HCl
what stops the stomach from digesting itself
the mucosal barrier
how does the mucosal barrier work
- tight junctions between mucosal epithelial cells prevents leakage of gastric juice onto underlying tissue
- mucous secreted by epithelial/goblet cells has a higher pH, providing localised neutralisation and physical barrier to acid
- prostaglandins increase mucosal thickness and stimulate bicarbonate production
what are the three phases of gastric secretion
- cephalic phase
- gastric phase
- intestinal phase
what happens and stimulates the cephalic phase
increased secretion.
drop in blood glucose
stimulated by sight, smell taste, thought of food
