Stomach

Question 0

Describe the components of gastric secretions and their cellular origins

Answer 0

Attack:
Chief cells - enzymes (pepsin)
Parietal cells - acid
Defence:
Neck cells - mucus
Endocrine cells - gastrin

Question 1

Describe the functions of the stomach

Answer 1

Stores food
Disinfects food
Breaks food down to chyme

Question 2

Explain the mechanics of secretion of stomach acid

Answer 2

In mitochondrion:
H2O –> H+ OH-
OH- + CO2 –> HCO3- (into bloodstream)
In parietal cell:
Mitochondria provide energy for proton pumps
H+ ions pumped into canaliculi –> stomach lumen

Question 3

Explain the control of gastric acid secretion

Answer 3

Gastrin –> bind to surface receptor –> secondary messanger pathway
Histamine –> bind to H2 surface receptor –> cAMP
ACh –> muscarinic receptor –> secondary messenger pathway
Peptides, ACh –> stimulate gastrin
Distension, CNS –> stimulate ACh
Gastrin, ACh –> stimulate histamine

Question 4

Outline the ways in which gastric acid secretion may be reduced by drugs

Answer 4

NSAIDS inhibit acid secretion

Question 5

Describe the function of the stomach defences

Answer 5

Mucus
Unstirred layer (H+ reacts with mucus –> HCO3-)
Prevent stomach epithelia from being damaged by acid
Prevent ulceration

Question 6

Describe the patterns of motility of the stomach, including receptive relaxation and peristalsis

Answer 6

Receptive relaxation - stomach relaxes as it is filled with food to prevent reflux
Peristalsis - 3x/min, rate of acceleration of peristaltic wave
Stomach emptying = rate of digestion

Question 7

Describe the process of gastric emptying and its control

Answer 7

Gastric emptying = rate of digestion 
Cephalic:
Detected and ingested food
Autonomic
Gastric:
Increased pH
Stomach distends
Digestion releases peptides --> histamine release
Intestinal:
Stomach empties
Chyme --> release of hormones --> decreased gastrin 
Low pH --> decreased gastrin

Question 8

Describe the gross structure, parts and curvatures of the stomach

Answer 8

Greater curvature - LHS
Lesser curvature - RHS
Cardia, fundus, body, antrum, pylorus