Stomach function

Question 1

What are the basic functions of the stomach?

Answer 1

Short-term storage of food

Disrupt food

Continue digestion of food

Disinfect the food

Question 2

Why does the stomach need to store food?

Answer 2

Because we eat faster than we digest and absorb

Question 3

How is the stomach adapted to storing food?

Answer 3

It has temporary folds called rugae

these can unfold, expanding the stomach

Question 4

How else does the stomach store food, apart from unfolding rugae?

Answer 4

Receptive relaxation

-vagovagal reflex

Question 5

What is the vagovagal reflex?

Answer 5

Mechanoreceptors in stomach wall detect stretch
vagal afferents carry this sensory information to medulla
vagal efferents to smooth muscle in stomach wall cause it to relax
stomach expands

Question 6

What is the importance of the stomach expanding to store food?

Answer 6

Intra-gastric pressure is not increased

prevents reflux of gastric contents into oesophagus

Question 7

How does the stomach disrupt the food?

Answer 7

Muscular contractions of its wall

mix contents

Question 8

How is the stomach adapted to disrupting food?

Answer 8

Has an extra layer of smooth muscle in its muscularis externae
called the oblique layer

Question 9

How does the stomach mix its contents?

Answer 9

Every 15-20 seconds
waves of peristalsis from proximal to distal parts of stomach
these get more intense in the distal stomach

Question 10

Why do the waves of peristalsis get more intense in the distal stomach?

Answer 10

Because it has a thicker muscular wall than the proximal stomach

Question 11

How does the stomach continue digestion of the food?

Answer 11

Chief cells secrete pepsinogen
which is activated to form pepsin
and that digests proteins

Question 12

How is pepsinogen activated into pepsin?

Answer 12

By hydrocholoric acid in stomach

secreted by parietal cells

Question 13

What is the function of hydrochloric acid in the stomach, apart from activating pepsinogen into pepsin?

Answer 13

Innate chemical barrier, kills bacteria

disinfects the food

Question 14

How do parietal cells secrete hydrochloric acid?

Answer 14

H+ K+ ATPase on apical domain of parietal cell
actively transports one hydrogen ion out of cell into stomach lumen and one potassium ion into cell from stomach lumen

AE on basolateral domain of parietal cell
moves bicarbonate ion from cell into interstitial fluid, chloride ion from interstitial fluid into cell

Chloride on channel on apical domain of parietal cell
chloride ions move through from cell into stomach lumen

Question 15

Where do the hydrogen and bicarbonate ions in parietal cells come from?

Answer 15

Carbon dioxide reacts with water
reaction is catalysed by carbonic anhydrase
produces hydrogen ion and bicarbonate ion

Question 16

What is the effect of the AE on the basolateral domain of the parietal cell moving bicarbonate ions into the interstitial fluid?

Answer 16

They diffuse into the plasma
makes the plasma of venous blood leaving the stomach more alkaline
called the alkaline tide

Question 17

What stimulates the secretion of hydrochloric acid from parietal cells?

Answer 17

Gastrin secreted by G cells

Histamine secreted by enterochromaffin cells

Acetylcholine from vagus nerve

Question 18

How does histamine interact with parietal cells to stimulate them to secrete hydrochloric acid?

Answer 18

Binds to H2 receptors on parietal cells

Question 20

How does gastrin interact with parietal cells to stimulate them to secrete hydrochloric acid?

Answer 20

Binds to CCK receptor on parietal cells

Question 21

What stimulates the vagus nerve to release acetylcholine?

Answer 21

Vagovagal reflex

Question 22

How does acetylcholine interact with parietal cells to stimulate them to secrete hydrochloric acid?

Answer 22

Binds to muscarinic receptors on parietal cells

Question 23

What stimulates G cells to secrete gastrin?

Answer 23

Peptides or amino acids in stomach lumen

Acetylcholine from vagus nerve

Gastrin-releasing peptide from vagus nerve

Question 24

How does acetylcholine interact with G cells to stimulae them to release gastrin?

Answer 24

Binds to muscarinic receptors on G cells

Question 25

How does gastrin-releasing peptide interact with G cells to stimulate them to release gastrin?

Answer 25

Binds to GRP receptors on G cells

Question 26

What inhibits the release of gastrin from G cells?

Answer 26

Somatostatin secreted by D cells

Question 27

How does somatostatin interact with G cells to inhibit the release of gastrin?

Answer 27

Binds to somatostatin receptors on G cells

Question 28

What stimulates D cells to secrete stomatostatin?

Answer 28

Low pH

Question 29

When is there a low pH in the stomach?

Answer 29

When food leaves the stomach as chyme | because food present in the stomach lumen acts as a buffer of gastric acid

Question 30

What are the phases of gastric secretion?

Answer 30

Cephalic Gastric Intestinal

Question 31

When does the cephalic phase of gastric secretion occur?

Answer 31

Before the food has reached the stomach

Question 32

What happens in the cephalic phase of gastric secretion?

Answer 32

Smell, taste, chewing, swallowing etc. are stimuli vagal efferents to G cells, parietal cells release acetylcholine stimulates G cells to secrete gastrin, parietal cells to secrete hydrochloric acid release gastrin-releasing peptide stimulates G cells to secrete gastrin

Question 33

When does the gastric phase of gastric secretion occur?

Answer 33

When the food is in the stomach

Question 34

What happens in the gastric phase of gastric secretion?

Answer 34

Vagovagal reflex releases acetylcholine, gastrin-releasing peptide... stimulates G cells to secrete gastrin, parietal cells to secrete hydrochloric acid Amino acids and small peptides in stomach lumen stimulates G cells to secrete gastrin Food in stomach buffers low pH less somatostatin secreted from D cells less inhibition of G cells secreting gastrin

Question 35

When does the intestinal phase of gastric secretion occur?

Answer 35

When chyme enters the duodenum from the stomach

Question 36

What happens in the intestinal phase of gastric secretion?

Answer 36

Partially digested proteins in chyme in duodenum stimulates G cells in duodenum to secrete gastrin stimulates parietal cells in the stomach to secrete hydrochloric acid Reverse enterogastric reflex Inhibitory hormone released

Question 37

What stimulates the reverse enterogastric reflex?

Answer 37

Lipids in chyme in duodenum

Question 38

What happens in the reverse enterogastric reflex?

Answer 38

Reduced vagus nerve stimulation

Question 39

What inhibitory hormone is released in the later intestinal phase of gastric secretion?

Answer 39

Secretin

Question 40

What are the functions of secretin?

Answer 40

Inhibits release of hydrochloric acid from parietal cells

Question 41

Which phases of gastric secretion contribute most to the total secretion of hydrochloric acid from parietal cells?

Answer 41

Gastric phase then cephalic phase then intestinal phase

Question 42

What protects the stomach epithelial from damage by hydrochloric acid?

Answer 42

Thick mucus layer acts as a physical barrier also contains bicarbonate ions, neutralises acid Epithelial cells proliferate old ones replaced with new ones quite often Prostaglandins

Question 43

How do prostaglandins protect stomach epithelial cells?

Answer 43

Maintain mucosal blood flow | increased delivery of nutrients to epithelial cells

Question 44

How does the stomach only allow chyme to move through the duodenum, and not larger parts of food?

Answer 44

Stomach contents accelerate as they move downwards leaves larger parts behind liquid chyme reaches pylorus Pyloric sphincter controls what passes through from stomach to duodenum only allows chyme to pass through it

Question 45

How often does chyme move into the duodenum during gastric emptying?

Answer 45

3 times a minute

Question 46

What are the different parts of the stomach mainly responsible for secreting?

Answer 46

Cardia -mucus Fundus and body - mucus - hydrochloric acid - pepsinogen Pyloris - gastrin - somatostatin

Question 47

What inhibits the release of hydrochloric acid from parietal cells?

Answer 47

Somatostatin secreted by D cells inhibit release of gastrin from G cells and histamine from enterochromaffin cells which reduces the secretion of hydrochloric acid from parietal cells