Functions Of The Stomach

Question 1

What are the basic functions of the stomach?

Answer 1

Short term storage of food
Mechanical and chemical disruption of food
Continue digestion (proteins mainly)
Disinfect

Question 2

What epithelium lines the stomach?

Answer 2

Simple columnar

Question 3

What are rugae?

Answer 3

Fold in the mucosa and submucosa

Allow distension of the stomach

Question 4

How many layers of smooth muscle are there in the stomach?

Answer 4

3

Question 5

Why do we want to grind our food?

Answer 5

Increase the surface area for enzymes to work on

Question 6

Describe receptive relaxation of the stomach

Answer 6

Vagus nerve mediated
Allows food to enter the stomach without raising the intragastric pressure too much
Prevents reflux
Distension of rugae

Question 7

Why do we have acidic conditions in the stomach?

Answer 7

Help to unravel protein
Activates proteases
Disinfects stomach contents

Question 8

What do the parietal cells secrete?

Answer 8

HCl and intrinsic factor

Question 9

What do the G cells secrete?

Answer 9

Gastrin

Question 10

What do the enterochromaffin like cells (ECL) secrete?

Answer 10

Histamine

Question 11

What do the chief cells of the stomach secrete?

Answer 11

Pepsinogen

Question 12

What do the D cells secrete?

Answer 12

Somatostatin

Question 13

What do the mucous cells in the stomach secrete?

Answer 13

Mucus

Question 14

What is the predominant secretion in the cardia of the stomach?

Answer 14

Mucus

Question 15

What is secreted in the body and fundus of the stomach?

Answer 15

Mucus, HCl, pepsinogen

Question 16

What is secreted at the pylorus of the stomach?

Answer 16

Gastrin, somatostatin

Question 17

The parietal cells are stimulated to release HCl via …

Answer 17

Gastrin
Histamine
ACh

Question 18

How are parietal cells adapted for acid release?

Answer 18

Have many invaginations of the cell membrane to increase the surface area for acid release

Question 19

What receptors are present on the parietal cells and what binds to them?

Answer 19

CCK receptor - gastrin binds
H2 receptor - histamine
Muscarinic receptor - ACh

Question 20

What stimulates gastrin secretion?

Answer 20

Peptides/amino acids in the stomach lumen

Vagal stimulation

Question 21

Where are the G cells located?

Answer 21

Antrum

Question 22

What factors inhibit HCl production?

Answer 22

Inhibition of G cells - less gastrin
Food leaving the stomach, decrease in pH, activates D cells - somatostatin which inhibits G cells
Stomach distension reduces - reduced vagal stimulation
Somatostatin also prevents the production of histamine

Question 23

Describe HCl production

Answer 23

Water split inside the parietal cells (OH- and H+)
H+ moved into stomach lumen
Cl- moved into stomach lumen (the 2 combine)
CO2 combines with the OH- forming bicarbonate which is moved into the blood stream creating the alkaline tide during acid production

Question 24

Describe the antiporter present on the basolateral surface of parietal cells

Answer 24

HCO3- moves into blood (out of cell)

Cl- moves into cell (out of blood)

Question 25

How do we scientifically write the proton pump?

Answer 25

H+/K+/ATPase

Question 26

How does the proton pump work?

Answer 26

Uses ATP to pump H+ into stomach lumen against huge conc gradient In exchange for a K+ ion

Question 27

What are the 3 phases of digestion?

Answer 27

Cephalic Gastric Intestinal

Question 28

Describe the cephalic phase of digestion

Answer 28

``` Before things arrive in the stomach 30% total HCl secreted PNS stimuli - direct stimulation of parietal and G cells via vagus nerve Anticipating food Also increases gastric motility slightly ```

Question 29

Describe the gastric phase of digestion

Answer 29

Food actually in the stomach 60% of total HCl secreted in this stage Distension stimulates vagus -> parietal and G cells Presence of amino acids -> G cells Food acts as a buffer Enteric NS and gastrin cause strong muscular contractions - acceleration of food towards pyloric sphincter

Question 30

Describe the intestinal phase of digestion

Answer 30

10% of HCl production done in this phase Chyme initially stimulates HCl secretion Soon overtaken by inhibiton of G cells Presence of lipids activates enterogastric reflex - reduced vagal stimulation - reduced secretions Chyme stimulates CCK and secretin which help suppress secretions

Question 31

Name some factors that protect the stomach

Answer 31

Mucus Bicarbonate Rapid turnover of epithelial cells

Question 32

Why do we need the thick alkaline layer at the epithelium in the stomach?

Answer 32

Higher pH so that proteases are not activated near the stomach surface

Question 33

Why are NSAIDs bad for the stomach?

Answer 33

Reduce synthesis of prostaglandins Decrease the mucosal blood flow Decreased nutrients to epithelium Breaching stomach defences

Question 34

How does alcohol breach the stomach defences?

Answer 34

Dissolves the mucus layer

Question 35

What is the most effective way to stop acid production?

Answer 35

PPIs | Eg. Omeprazole, lansoprazole

Question 36

Give examples of H2 antagonists

Answer 36

Cimetidine | Ranitidine