s4. stomach 1 and 2

Question 1

role of the stomach

Answer 1

storage facility
start digestion of protein
continue digestion of carb and fat
disinfect> innate defence

Question 2

anatomical areas of stomach

Answer 2

funds- top portion
cardia- ‘neck’ kind of area where oesophagus meets stomach
body- main bulk
antrum- narrower distal area

Question 3

importance of pyloric sphincter

Answer 3

muscle which controls release of acidic chyme into duodenum

Question 4

describe epithelial cell type of oesophagus compared to stomach

Answer 4

oesophagus= stratified squamous
stomach= simple columnar

Question 5

which muscles prevent reflux of food from stomach into oesophagus

Answer 5

Lower Oesophageal sphincter
intrinsic smooth muscle
Right Crus of diaphragm > closes when intra abdominal pressure increases

Question 6

what is receptive relaxation

Answer 6

peristalsis alerts stomach when foods swallowed and there’s a reflex relaxation of proximal stomach musculature> so stomach can expand

• funds descends
• stomach can fill w/o significant rise in pressure

Question 7

importance of rugae

Answer 7

folds within stomach> ensures pressure doesn’t change too drastically when filled as accommodates when filled

Question 8

parts of diaphragm

Answer 8

costal diaphragm

crural part > right crus aids stomach reflux

Question 9

another concept that prevents reflux (non musculature)

Answer 9

acute angle entrance from oesophagus to stomach > prevents contents going back up when high intaabdominal pressure

Question 10

muscles of stomach

Answer 10

oblique (inner most)
circular
longitudinal

> forceful contractions
mechanically breakdown food

Question 11

describe the change in musculature from proximal to distal stomach

Answer 11

proximal- thinner walled

distal- more muscular

Question 12

relevance of the thicker distal wall of stomach

Answer 12

the thicker distal wall helps move smaller particles towards pyloric sphincter to s. intestine
leave larger particles to get smaller in stomach
> separates contents

Question 13

what are gastric pits

Answer 13

found on surface of stomach

invaginations of epithelia >lead to gastric glands

Question 14

which cells found on surface of stomach

Answer 14

surface mucous cells>secrete mucous

>forms protective layer between acidic lumen and epithelial layer

Question 15

what cells are found in gastric glands

Answer 15

parietal cells> produce acid
chief cells> produce pepsinogen (inactive form of pepsin)
enteroendocrine cells (G cells- gastrin release. facilitate acid production)

Question 16

which area of stomach are G cells most commonly found

Answer 16

antrum (distal end if stomach)

Question 17

which area of stomach are parietal cells most commonly found

Answer 17

body of stomach

Question 18

describe protective mechanisms of stomach

Answer 18

• prostaglandin release
  >inc mucosal blood flow
  > support mucus layer
  >generally protective
• rich blood supply >move acid away quickly
• high epithelial cell turnover >if damaged quickly replaced to keep intact epithelial layer
• epithelia produce HCO3 > produce pH neutral layer

Question 19

which cell controls acid secretion

Answer 19

parietal cell via proton pump exchange between H+ and K+

Question 20

compare parietal cell in resting vs active phase

Answer 20

Resting phase:
Tubulovesicles > lack K+ permeability

Active phase:
Tubulovesicles make contact with apical membrane (which contains K+ channels)
via the canaliculi

Question 21

3 phases of digestion

Answer 21

Cephalic
Gastric
Intestinal

Question 22

what stimulates acid production

Answer 22

sensory triggers
e.g. smell sight taste

gastric triggers
e.g. stretch, presence of aa and small peptides
(produce most acid here)

intestinal triggers
e.g. chyme in duodenum
presence of partially digested proteins

Question 23

what stimulates parietal cell?

Answer 23

gastrin receptors
histamine receptors
muscarinic receptors (Ach)

Question 24

describe gastrin stimulation of parietal cell

Answer 24

peptides and aa stimulate gastrin to be released from G cell.
gastrin binds with CCK receptor on parietal cell (cholecystokinin)

Question 25

describe vagal stimulation of G cell

Answer 25

acetylcholine and muscarinic receptor

gastric releasing peptide (GRP) > sensitive to stretch

Question 26

describe histamine stimulation of parietal cell

Answer 26

Entero-chromaffin like cell (ECL) produces histamine which binds to H2 receptor on parietal cell

ECL stimulated by Ach and gastrin.

Question 27

how is acid secretion inhibited?

Answer 27

D cell producing somatostatin
> inhibiting hormone. inhibits G cells y binding to them via somatostatin receptors

> less gastrin produced

Question 28

how is HCl produced in the parietal cell

Answer 28

H20 and CO2 within parietal cell combine to form carbonic acid (H2CO3)
> dissociates into H+ and HCO3- ions.
via carbonic anhydrase enzyme in cytosol of parietal cell
> H+ ions then pumped across apical membrane into stomach lumen through proton pump (NaK ATPase)
> H+ form with Cl- in lumen

• As H+ is pumped out via proton pump, K+ enters so there is also a K+ channel on apical membrane to pump the K+ back out to lumen

Question 29

what is alkaline tide

Answer 29

raise in pH of venous blood leaving stomach