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gihep 9: gastric function (i) (gastrin releasing peptide (postgang fibres…
gihep 9: gastric function (i)
proximal 1/3 of stomach
storage
up to 1500ml without changing pressure
receptive relaxation
distension causes reflex relaxation
involves local + central Ns, + NO
distal 2/3 of stomach
mixing + propulsion
spontaneous electricity @ pacemaker region -> depol -> AP @ threshold -> contractions
depol agents = vagus (ACh), hormones (gastrin), distension (enteric reflex)
narrow pyloric sphincter
only small amount of food enters duodenum per contraction (rest pushed back into stomach)
digestion in stomach
salivary amylase deactivated by low pH
Pepsin for protein digestion activated by low pH
esp collagen from meat
gastric juice
swallowed saliva
products from stomach
H2O,HCl,pepsin,mucus,bicarb,Na,K
reflux from duodenum
bile, pancreatic juice
1500ml per day
Oxyntic glands
in proximal + some of distal stomach
several cell types
mucous neck cells
secret mucus + pepsinogen
peptic/chief cells
secrete pepsinogen
oxyntic/parietal cells
secrete HCl + intrinsic factor (for B12 absorption)
D cells
secrete somatostatin (acts on chief cells)
Mast-like cells
secrete histamine (acts on chief cells)
Pyloric glands
in pyloric antrum
mostly mucous cells
G cells (secrete gastrin into blood)
D cells
Surface epithelial cells
mucus
contains mucins + bicarb
lubrication + protection from acid
gastrin releasing peptide
postgang fibres of vagus stimulate G cells to produce it
autocrine
stimulates G cells to make gastrin
small amount made in cephalic phase (before food)
large amount made in gastric phase (food ingested)