pancreas

Question 1

stimuli of bicarbonate secretion

Answer 1

presence of acid chyme in proximal duodenum

Question 2

effect of decrease in pH (acid) in pancreas on HCO3- efflux into pancreatic juice

Answer 2

activates S-cells in luminal wall → release secretin → moves into bloodstream to pancreas → binds to basolateral duct cell receptors → increase IC cAMP concentration → activation of Cl- channels in apical membrane → efflux of Cl- → Cl-/HCO3- anion exchange into pancreatic juice

Question 3

effect of HCO3- efflux on pH

Answer 3

bicarbonate-rich fluid moves along ducts into duodenum (via ampulla of vater and sphincter of oddi); bicarbonate reaches lumen as acid chyme moves across secretion, reducing free acid available, forming carbonic acid, water and CO2

Question 4

consequence on enzyme activity of returning to normal higher pH in pancreas

Answer 4

more optimal so increase rates of reactions

Question 5

pancreatic regulation after ingestion of mixed meal (fats and peptides): hormonal imput

Answer 5

I-cells and S-cells in duodenal wall detect fats and peptides → CCK released from I-cells, secretin released from S-cells → CCK travels in blood to pancreas via hepatic circulation, venous drainage and systemic arteriole system → binds to CCK-1 receptors on acinar cells on basolateral surface → activation of PLC and IP3 seconday messenger system → increase in cytosolic Ca2+ → exocytosis of granules containing zymogens, inhibitors and active enzymes → secreted into terminal ducts of pancreatic ducts → secretin binds to duct cells and stimulates secretion of watery HCO3- rich fluid → move out into duodenum → activated by enterokinase → trypsinogen converted to trypsin → activates other zymogens

Question 6

pancreatic regulation after ingestion of mixed meal (fats and peptides): central imput

Answer 6

vagus nerve secretes acetylcholine → binds to muscarinic receptors on acinar cells → activation of PLC and IP3 seconday messenger system → increase in cytosolic Ca2+ → exocytosis of granules containing zymogens, inhibitors and active enzymes → secreted into terminal ducts of pancreatic ducts → move out into duodenum → activated by enterokinase

Question 7

3 phases of pancreatic secretion and proportions

Answer 7

cephalic (20%), gastric (10%), intestinal (70%)

Question 8

stimuli of cephalic phase

Answer 8

thought, sight, smell and taste of food

Question 9

key mediator of cephalic phase

Answer 9

vagus nerve

Question 10

activated cells of cephalic phase

Answer 10

acinar cells

Question 11

stimuli of gastric phase

Answer 11

mechanoreceptors detect distension of stomach

Question 12

key mediator of gastric phase

Answer 12

vagus nerve

Question 13

activated cells of gastric phase

Answer 13

acinar cells

Question 14

stimuli of intestinal phase

Answer 14

acid and nutrient detection in proximal duodenum (acid chyme; S and I-cells)

Question 15

key mediator of intestinal phase

Answer 15

hormones (act on stimuli of intestinal phase by negative feedback, as pH increases and products digested)

Question 16

activated cells of intestinal phase

Answer 16

acinar cells, duct cells

Question 17

effect of bicarbonate secretion of infusion of CCK alone

Answer 17

no effect

Question 18

effect of bicarbonate secretion of infusion of secretin alone

Answer 18

increases bicarbonate secretion

Question 19

effect of bicarbonate secretion of infusion of CCK and secretin

Answer 19

CCK amplifies effect of secretin on bicarbonate secretion

Question 20

effect of secretin on CCK-mediated enzyme secretion from acinar cells

Answer 20

no effect

Question 21

rate of HCO3- compared to duodenal pH

Answer 21

at higher pH (more alkali), less HCO3- released as already sufficiently alkali; as pH decreases (causing damage to duodenum epithelia and outside optimum enzyme pH), more HCO3- secreted; only up to pH 5 as other HCO3- secretions occur (e.g. Brunner’s cells, bile)