gastric acid secretion - regulation

Question 1

what are the contents of normal gastric juice in the fasting state

Answer 1

cations: na, k, mg, h
anions: cl, hpo4, so4
pepsins, lipase
mucus
intrinsic factor

Question 2

normal pH of fasting gastric juice

Answer 2

about 3.0

Question 3

what are secreted by the fundus and body of the stomach

Answer 3

mucus
HCl
pepsinogen
ALL EXOCRINE

Question 4

what are secreted by the antrum

Answer 4

dec HCl

inc gastrin

Question 5

what are the walls of tubular glands in epithelial cells lined with

Answer 5

parietal cells

Question 6

what do parietal cells secrete

Answer 6

HCl and intrinsic factor

Question 7

What do enterochromaffin-like cells (ECL) secrete

Answer 7

paracrine agents eg histamine

Question 8

how is gastric acid made in the stomach lumen

Answer 8

bicarb exhanged for Cl- in the blood - acidity of venous blood from stomach is dec c.f. blood serving it.
excess Cl- diffused into stomach through cl channels; H+ pumped into stomach via K+ATPase
results in net flow of H+ and Cl- out of parietal cell and into lumen

Question 9

how does mucus protect against H+ secretion

Answer 9

inc HCO3 forms water insoluble gel on epithelial surface

Question 10

effect of lipase on triglycerides

Answer 10

converts into fatty acids and triglycerol

Question 11

what does intrinsic factor do

Answer 11

prevents pernicious anemia - absorbs Vit B12

Question 12

what does HCl do

Answer 12

kills bacteria
denatures digested food
activates PEPSINOGEN

Question 13

What are the phases of HCl secretion by parietal cells

Answer 13

cephalic
gastric
intestinal

Question 14

what regulates HCl secretion

Answer 14

neuronal pathways, duodenal hormones

Question 15

how do neuronal pathways and duodenal hormones regulate secretion of HCL

Answer 15

1. directly, on parietal cell
2. indirectly influence gastrin and histamine secretion
   BOTH UPREGUALTE ACID SECRETION

Question 16

how is gastric acid secretion regulation in the cephalic phase

Answer 16

ach released
stimulated release of histamine from ECL cells
ach acts directly on parietal cells - inc HCl

Question 17

how is gastric acid secretion regulated in the gastric phase

Answer 17

stomach distension inc pepitde conc

inc acidity/ lowering of [H+]

Question 18

why is the acidity of the lumen of the stomach higher before a meal

Answer 18

no bueffers

Question 19

what do proteins do to luminal acidity

Answer 19

act as buffers in the gastric lumen - so HCl secretion increases

Question 20

mechanism for effect of proteins on luminal acidity

Answer 20

proteins remove free H+ - their conc decreases; proteins remove inhibitory effect of HCl on gastrin and therefore acid secretion
gastrin-mediated acid secretion is increased

Question 21

summary of gastric phase

Answer 21

food in stomach:

1. distension - neural reflex - ach on parietal cells
2. buffers acid - blocks stimulation of somatostatin secretion
3. peptides, AAs, act on G cells for gastrin release

Question 22

what increases gastrin secretion

Answer 22

luminal distension, inc activity of PSNS nerves to stomach

Question 23

what inhibits gastrin secretion

Answer 23

increased HCl secretion

Question 24

what does gastrin secretion promote

Answer 24

histamine secretion, acid secretion from parietal cells

Question 25

what can act on parietal cells to increase acid secretion

Answer 25

gastrin, histamine | increased activity of PSNS nerves on stomach

Question 26

function of the intestinal phases of gastric acid secretion

Answer 26

balances secretory activity of stomach and digestive/absorptive capacities of the SI

Question 27

how does the high acidity of the duodenal contents affect acid secretion

Answer 27

reflexly inhibits it

Question 28

what can inhibit acid secretion

Answer 28

``` duodenal distension hypertonic solution AA fatty acids monosaccharides ```

Question 29

what does inhibition of acid secretion in the SI depend on

Answer 29

chyme volume and composition

Question 30

how is acid secretion inhibited in the intestinal phase

Answer 30

short and long neuronal reflexes, hormones eg secretin and CCK inhibit parietal cell acid secretion

Question 31

what can lack of HCl result in

Answer 31

failure of protein digestion - production of gastric acid in the stomach is absent or low

Question 32

symptoms of HCl deficiency

Answer 32

undigested food in stool flatulence, bloating lack of intrinsic factor

Question 33

treatment of HCl deficiency

Answer 33

bitter herbs lemon juice, vinegar, vit b1 all stimulate HCl secretion

Question 34

other ways HCl secretion can be stimulated

Answer 34

``` caffeine alcohol nsaids nicotine h. pylori stress ```

Question 35

effect of histamine on gastric acid secretion

Answer 35

inhibition

Question 36

effect of histamine / ach/ gastrin on binding to parietal cells -

Answer 36

increased HCl secretion

Question 37

where is pepsin secreted from

Answer 37

chief cells as pepsinogen

Question 38

how is pepsinogen activated

Answer 38

high [proton] - high acidity exposes its active site

Question 39

how is pepsinogen inactivated

Answer 39

entry of food into SI - HCO3 - and peptides neutralise H+

Question 40

what stimulates pepsinogen secretion

Answer 40

inputs to chief cells from nerve plexus | stimulators/inhibitors of acid secretion in cephalic and intestinal phases exert the same effect on pepsinogen secretion

Question 41

what does pepsin do

Answer 41

initiates protein digestion - degrades proteins in food into peptides

Question 42

pepsin in not required for food digestion, but what is?

Answer 42

intrinsic factor - secreted by the parietal cells

Question 43

how do NSAIDS eg aspirin affect acid secretion

Answer 43

impair barrier properties of mucosa supress gastric prostaglandin synthesis - COX inhibtion inhibit platelet aggregation