s4. stomach 1 and 2 Flashcards
role of the stomach
storage facility
start digestion of protein
continue digestion of carb and fat
disinfect> innate defence
anatomical areas of stomach
funds- top portion
cardia- ‘neck’ kind of area where oesophagus meets stomach
body- main bulk
antrum- narrower distal area
importance of pyloric sphincter
muscle which controls release of acidic chyme into duodenum
describe epithelial cell type of oesophagus compared to stomach
oesophagus= stratified squamous stomach= simple columnar
which muscles prevent reflux of food from stomach into oesophagus
Lower Oesophageal sphincter
intrinsic smooth muscle
Right Crus of diaphragm > closes when intra abdominal pressure increases
what is receptive relaxation
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
importance of rugae
folds within stomach> ensures pressure doesn’t change too drastically when filled as accommodates when filled
parts of diaphragm
costal diaphragm
crural part > right crus aids stomach reflux
another concept that prevents reflux (non musculature)
acute angle entrance from oesophagus to stomach > prevents contents going back up when high intaabdominal pressure
muscles of stomach
oblique (inner most)
circular
longitudinal
> forceful contractions
mechanically breakdown food
describe the change in musculature from proximal to distal stomach
proximal- thinner walled
distal- more muscular
relevance of the thicker distal wall of stomach
the thicker distal wall helps move smaller particles towards pyloric sphincter to s. intestine
leave larger particles to get smaller in stomach
> separates contents
what are gastric pits
found on surface of stomach
invaginations of epithelia >lead to gastric glands
which cells found on surface of stomach
surface mucous cells>secrete mucous
>forms protective layer between acidic lumen and epithelial layer
what cells are found in gastric glands
parietal cells> produce acid
chief cells> produce pepsinogen (inactive form of pepsin)
enteroendocrine cells (G cells- gastrin release. facilitate acid production)
which area of stomach are G cells most commonly found
antrum (distal end if stomach)
which area of stomach are parietal cells most commonly found
body of stomach
describe protective mechanisms of stomach
- 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
which cell controls acid secretion
parietal cell via proton pump exchange between H+ and K+
compare parietal cell in resting vs active phase
Resting phase:
Tubulovesicles > lack K+ permeability
Active phase:
Tubulovesicles make contact with apical membrane (which contains K+ channels)
via the canaliculi
3 phases of digestion
Cephalic
Gastric
Intestinal
what stimulates acid production
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
what stimulates parietal cell?
gastrin receptors
histamine receptors
muscarinic receptors (Ach)
describe gastrin stimulation of parietal cell
peptides and aa stimulate gastrin to be released from G cell.
gastrin binds with CCK receptor on parietal cell (cholecystokinin)
describe vagal stimulation of G cell
acetylcholine and muscarinic receptor
gastric releasing peptide (GRP) > sensitive to stretch
describe histamine stimulation of parietal cell
Entero-chromaffin like cell (ECL) produces histamine which binds to H2 receptor on parietal cell
ECL stimulated by Ach and gastrin.
how is acid secretion inhibited?
D cell producing somatostatin
> inhibiting hormone. inhibits G cells y binding to them via somatostatin receptors
> less gastrin produced
how is HCl produced in the parietal cell
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
what is alkaline tide
raise in pH of venous blood leaving stomach
