Lecture 35 - Gastric physiology

Question 1

what are the 4 main functions of the stomach

Answer 1

1. storage
2. “grinding down” of food
3. controlled delivery rate of food to the duodenum
4. acid secretion and regulation

Question 2

as food enters the stomach, the stomach relaxes in a process called ____

Answer 2

receptive relaxation/accomodation

Question 3

give the function of the stomach product:

H+ ion

Answer 3

kills microbes, converts pepsinogen into pepsin and denatures protein

Question 4

give the function of the stomach product:

pepsinogen

Answer 4

partial digestion of protein

Question 5

give the function of the stomach product:

mucus

Answer 5

lubricates and protects mucosa

Question 6

give the function of the stomach product:

bicarbonate

Answer 6

protects mucosa

Question 7

give the function of the stomach product:

intrinsic factor

Answer 7

needed for normal absorption of B12

Question 8

give the function of the stomach product:

water

Answer 8

dissolves and dilutes ingested material

Question 9

give the function of the stomach product:

gastrin

Answer 9

stimulates acid secretion
regulates mucosal growth
stimulate pepsinogen secretion

Question 10

give the function of the stomach product:

somatostatin

Answer 10

inhibits gastrin release

Question 11

what is the “true stomach” in a ruminant? why is it called this?

Answer 11

abomasum; secretes HCl and other digestive enzymes

Question 12

what is the cell type found lining the stomachs of ruminants, horses, and pigs

Answer 12

stratified squamous

Question 13

absorptive epithelium contains ____ and _____

Answer 13

NaCl; SCFA

Question 14

what are the 3 regions of mucosa in the stomach epithelium

Answer 14

1. cardiac
2. proper gastric
3. antral/pyloric mucosa

Question 15

describe the cardiac mucosa

Answer 15

cardiac glands secrete protective mucus and bicarbonate

Question 16

describe proper gastric mucosa

Answer 16

contains parietal glands, chief cells, enterochromaffin-like cells, and D cells

Question 17

describe antral/pyloric mucosa

Answer 17

contains D and G cells

Question 18

match the cell type to its secretion

a. parietal cells
b. chief cells
c. enterochromaffin-like cells
d. D cells
e. G cells

1. histamine
2. pepsinogen
3. gastrin
4. somatostatin
5. H+

Answer 18

a = 5
b = 2
c = 1
d = 4
e = 3

Question 19

parietal cells are also called _____

Answer 19

oxyntic glands

Question 20

describe the activation and action of:

parietal cells

Answer 20

produce HCl via a proton pump (activated by acetylcholine, histamine, and gastrin), creating an acidic environment to kill microbes

Question 21

describe the activation and action of:

G cells

Answer 21

produce gastrin in response to stretching of stomach wall, higher gastric pH, protein in chyme

Question 22

describe the activation and action of:

enterochromaffin cells

Answer 22

produce histamine in response to gastrin and pituitary peptides

Question 23

the gastric proton pump is inhibited by what 3 things

Answer 23

1. prostaglandins
2. antihistamines
3. somatostatin

Question 24

what are the 3 main mediators of gastric acid secretion

Answer 24

1. gastrin (acts on CCK and releases Ca2+)
2. histamine (acts on H2 and releases cAMP)
3. acetylcholine (acts on muscarinic cells and releases Ca2+)

Question 25

describe gastric acid secretion in 5 steps

Answer 25

1. gastric glands are stimulated and release H+ and Cl- 2. H+ is secreted through a proton pump in exchange for 1 K+ 3. H+ ions come from the dissociation of intracellular carbonic acid 4. as H+ is secreted, bicarbonate builds up in the cell 5. exchanges Cl- into cell

Question 26

gastrin release is stimulated by what 3 things

Answer 26

1. gastric distension 2. protein products in lumen of stomach 3. vagal stimulation

Question 27

acetylcholine comes from where

Answer 27

the vagus nerve

Question 28

what 3 inputs stimulate the vagus nerve

Answer 28

1. cephalic - sight, smell, physical presence of food 2. gastric - distension and products in lumen of stomach 3. intestinal - food in duodenum

Question 29

what is the most important mediatory of acid secretion? why?

Answer 29

histamine 1. ECL secretes it under most circumstances 2. activates messenger that synergizes other secondary messengers 3. H2 receptors are selectively expressed on parietal cells

Question 30

summarize inhibition of gastric secretion in 2 steps

Answer 30

1. stimuli that promote gastric secretion are not longer active 2. at low intragastric pH, D cells secrete somatostatin which inhibits gastric release

Question 31

the regulation of acid secretion is maintained by the relationship between

Answer 31

stomach volume, proton pump activity, and gastric acidity

Question 32

high acidity means ___ pump activity and a[n] ____ stomach

Answer 32

low; empty