Gastric Secretion Flashcards
What does the sight or smell of food stimulate
Cephalic reflex
Increased vagus nerve activity
What dos the vagus nerve do in the cephalic reflex
Releases Ach stimulating parietal cells
Innervates G cells which release Gastrin
What does gastrin and Ach do
Stimulates ECL to release histamine which acts on parietal cells
How is acid secreted
CO2 diffuses across membrane of parietal cells
Combined with H20 to make carbonic acid
Dissociates into hydrogen and bicarbonate
Bicarbonate transported out into blood and chloride pumped in
Hydrogen transported out into stomach lumen and K pumped in
Osmotic gradient pulls water out into lumen
Combined with chloride to make HCL
What enzyme facilitates
Carbonic anhydrase
How does Ach work
Increases Ca activating protein kinase and increased hydrogen K pump activity
How does gastrin work
Binds to G protein grouped receptor
Increases Ca
How does histamine work
Activates AC which converts ATP to cAMP and activating protein kinase
What does prostaglandin do
Switches off AC so no cAMP produced and decreased activity
What does somatostatin do
Released by stomach at end of meal and is inhibitory
What is the gastric phase of secretion stimulated by
Distention of stomach
Increases vagal and ENS
What does acid in the stomach stimulate
Pepsinogen release from chief cells through ENS reflex
Paralel to HCL secretion
What decreases vagal tone
Stopping eating
What is released if acid in duodenum
Secretin from S cells causing bicarbonate secretion from Brunner’s glands
Bicarbonate released from pancreas and liver - most from this
Gastrin production stopped so less acid secreted
Decreased emptying of stomach
What is released if fat in duodenum and what does this do (fat takes longer to digest)
CCK Decreased gastric motility Decreased acid secretion Increased zymogen Contraction of gall bladder Increased fullness
Wha does mucous contain
High levels of bicarbonate to neutralise acid
What is the purpose of mucous
Pepsin deactivated when enters mucous
Acid is buffered
So epithelial cells aren’t destroyed
What is the function of intrinsic factor
B12 absorption
Where is B12 absorped
Ileum
How does bicarbonate neutralise acid
Bicarbonate meets H from stomach to form carbonic acid
What produces strong contractions and grinds food
Antrum of stomach = thick muscle
What does contraction of pyloric sphincter allow
A small amount of gastric content to enter duodenum
Further mixing
What causes food to move down GI tract
Peristaltic waves
What produces peristaltic waves
PAcemker cells in longitudinal muscle layer
Basic electrical rhythm produces slow waves which is subthreshold for contraction
What is needed to make a contraction
Number of AP determines strength of contraction
What produces depolarisation and AP
Gastrin
Vagus nerve stimulation (para) - release Ach
What inhibits motlity
Fat, acid, AA, hypertonicity in duodenum
