Physiology: Gastric secretions

Question 1

which CN nerve relaxes the stomach?

Answer 1

CNX (vagus)

Question 2

rate of stomach emptying increases/ decreases when volume and consistency of chyme in the stomach increases?

Answer 2

increases

distension increases motility, activity of intrinsic nerve plexuses, vagus nerve activity, gastrin release

Question 3

what 2 responses does the duodenum use to delay gastric emptying when it is not yet ready to receive chyme?

Answer 3

• neuronal response: the enterogastric reflex (which decreases antral peristaltic activity via signalling from the intrinsic nerve plexuses and the autonomic nervous system)
• hormonal response: release of enterogastrones e.g. secretin and cholecystokinin (CCK) - these inhibit stomach contraction

Question 4

what are some duodenal factors that would intitiate the neuronal response(enterogastric reflex) and the hormonal response (enterogastron release) in order to delay gastric emptying?

Answer 4

fat
acid - time needed to neutralise this
hypertonicity
distension

Question 5

where is gastrin secreted from and what is its function?

Answer 5

secreted from G cells in the pyloric glands (located in the antrum)
it stimulates acid production from the parietal cells

Question 6

where is somatostatin secreted from and what is its function?

Answer 6

secreted from D cells in the pyloric glands (located in the antrum)
it is a potent inhibitor of gastric secretion (e.g. acid) and histamine

Question 7

where are parietal cells and what do they secrete?

Answer 7

they are in the fundus and body of the stomach

they secrete HCl and intrinsic factor

Question 8

where is histamine secreted from and what is its function?

Answer 8

secreted from enterochromaffin-like cells (located in the fundus and body)
it stimulates HCl secretion

Question 9

what is the precursor of pepsin? where is it secreted from?

Answer 9

precursor is pepsinogen, which is secreted by chief cells (located in the fundus and body)

Question 10

where is intrinsic factor produced, and what is its function?

Answer 10

produced by parietal cells (located in the oxyntic mucosa)

it binds vitamin B12, allowing for its absorption in the terminal ileum

Question 11

what are three things which stimulate HCl secretion from parietal cells?

Answer 11

histamine (strongest agonist)
gastrin
parasympathetic stimulation (via ACh to M3 receptors)

Question 12

what inhibits gastrin secretion between meals?

Answer 12

somatostatin (produced in the pyloric gland are by D cells)

Question 13

name the 3 phases of gastric secretion?

Answer 13

• cephalic (before food reaches stomach - e.g. sight, smell, taste of food)
• gastric (when food is in stomach - e.g. distension and protein digestion products stimulates gastric secretion)
• intestinal (after food has left stomach - e.g. the same factors that reduce gastric motility also reduce gastric secretion, as stomach empties, stimuli for secretion becomes less and less, secretion of somatostatin resumes)