Session 4- The Stomach

Question 1

functions of the stomach

Answer 1

storage
start digestion
a little bit of carb and fat digeston
disinfect

Question 2

what is chyme

Answer 2

resuly of stomach beginning digestion of proteins continuing digestion of fats and carbs

Question 3

what is the stomach made up of

Answer 3

fundus
body
antrum

Question 4

what type of epithelia is present

Answer 4

simple columnar

Question 5

where are the cardia

Answer 5

where the oesophagus joins the stomach close to heart

Question 6

receptive relaxtation of the stomach

Answer 6

peristalsis causes reflex relaxation of proximal stomach which causes the fundus to distend and then the stomach can fill without significant rise in pressure

Question 7

what are the muscles from innermost to outer

Answer 7

oblique
circular
longitudinal

they mechanically break down food by forceful contractions

Question 8

as you go down the stomach how does the tickeness of the wall change

Answer 8

gets thicker and more muscular

Question 9

what do parietal cells produce

Answer 9

hcl

Question 10

what do chief cells produce

Answer 10

pepsinogen which is converted to pepsin by the action of HCL which is produced by the parietal cells

Question 11

what is a G cell

Answer 11

enteroendocrine cell which is more prevalent in antral section in stomach
produce gastrin

Question 12

What do stomach epithelia secrete as protection

Answer 12

HCO3- into the mucus so eventually you get a layer that is neutral compared to the stomach lumen

Question 13

how do parietal cells produce acid

Answer 13

proton pump exchanges K+ with H + into the stomach lumen

Question 14

what stimulates acid production

Answer 14

smell
taste
sight 
stretch
presence of amino acids as small peptides
chyme in duodenum
presence of partially disgested proteins

Question 15

what stimulates a parietal cell - gastrin

Answer 15

peptides in the stomach lumen stimulate g cells to produce gastrin which binds to CCK receptors

Question 16

parietal cell stimulation- vagal

Answer 16

vagal stimulation of the cell through Mcr

also ACh binds ro G cells causing them to release gastrin which binds to CCK receptors

Question 17

how is an entero-chromaffin cell stimulated

Answer 17

vagal stimulation of entero-chromaffin like cell-ECL
histamine released which binds to H2 cell

there are also CCK receptors on the ECL so can be stimulated by gastrin

Question 18

how is acid secretion inhibited

Answer 18

D cells are stimulated by a drop in pH so produce somatostatin

Question 19

how is HCL produced

Answer 19

hydrgen ions from the H+/K+/ATPase combine with Cl- which diffuse into the stomach lumen

the hydrogen ions come from
H20 + C02 = H2C03 -carbonic anhydrage

the Cl- ions come from the HCO3-/Cl- exchanger on the basal surface

Question 20

Briefly explain to a friend why the parietal cell is unable to secrete acid during its resting
phase

Answer 20

During its resting phase the apical membrane of the parietal cell does not have any proton pumps (H+/K+ ATPases) associated with it as these are found (in the resting phase) within tubulovesicles in the cytosol of the cell.

Like wise the tubulovesicles only contain H+ component of the proton pump and need to be associated with the apical membrane to become functioning.

Therefore in its resting phase, the acid secreting mechanism (the proton pump) is
dissociated from itself and therefore no acid can be secreted.

Question 21

When the parietal cell is in its resting phase, what cytosolic structures contain the proton
pumps?

Answer 21

tubovesicles

Question 22

What receptor does the hormone Gastrin bind to on the parietal cell

Answer 22

CCK receptor

Question 23

How does the stomach separate out larger food molecules, that need to remain in the
stomach for further processing, from the smaller food molecules that can pass into the
duodenum?

Answer 23

The shape of the stomach is a funnel which means that when the stomach muscles contract the smaller molecules accelerate more quickly than the larger molecules, which separates them out, with the smaller molecules moving distally and the larger molecules staying in the body of the stomach for further processing.

Question 24

In simple terms explain why, when food enters the stomach, acid secretion is triggered

Answer 24

Food stretches the stomach activates vagal nerve stimulation of acid production

Food effectively raises the pH of the stomach by buffering the acid secretions. This removes the negative feedback on acid secretion that a low pH causes…therefore acid can be secreted.

Small peptides and amino acids are produced because of the action of pepsin in the
stomach and these stimulate acid secretion

Question 25

What are the various mechanisms that the stomach uses to resist injury from its own secretions

Answer 25

The stomach produces acid and proteases both of which could damage its structural
integrity (the stomach is made of protein).

The stomach is lined with surface mucous cells that secrete a mucus layer. Into this layer
bicarbonate ions are secreted so that a pH neutral barrier is formed.

The stomach mucosa also has a good blood supply that helps it H+ molecules that get
through the mucus barrier.

The stomach epithelia are replaced regularly so that damaged cells do not pose a threat to the integrity of the mucosa

Prostaglandins are released which boost the protective mechanisms in many ways,
especially by ensuring adequate mucosal blood flow.