Stomach

Question 1

Functions of stomach

Answer 1

Stores food
Mixes food with secretions
Regulates release of food into duodenum
Secretes gastric juice

Question 2

Functions of acid

Answer 2

Kills micro-organisms
Denatures proteins/enzymes in food
Activates pepsin
Breaks down plant cell walls + meat connective tissue

Question 3

Production of acid

Answer 3

In Parietal cells
H2o + co2 - h2co3 - H+ + Hc03 
The H+ is transported out into lumen via H-K ATPase pump (K in)
HC03 out into IS against CL
H + Cl join in lumen

Question 4

Where are cells in the stomach?

Answer 4

Fundus - chief + parietal cells

Pylorus/antrum - G + D cells

Question 5

Function of G, D, chief, parietal cells?

Answer 5

G - secrete gastrin - stimulates chief + parietal cells + stimulates contraction of gastric wall to mix

D - somatostatin - inhibits gastrin

Parietal - Hcl + Intrinsic Factor

Chief - secrete pepsinogen

Question 6

Control of acid secretion

Answer 6

Controlled by acetylcholine, histamine, gastrin + somatostatin 
Parietal cells have: 
M3 R
CCK R
H2 R
Somatostatin R

Ach from vagus nerve stimulates M3 on parietal, M3 on ECL cell, G cell with GRP and inhibits D cells

Question 7

Drug inhibitors of acid

Answer 7

PPIs - H-K ATPase pump inhibitor

H2 R antagonist e.g. ranitidine

Question 8

Inhibitors of acid

Answer 8

CCK - released from I cells in duodenum + jejunum in response to fat. Antagonises gastrin mediated acid production

Secretin - released from S cells in duodenum in response to fat + acid. Inhibits antral gastrin release + increases somatostatin release

Question 9

Phases of acid secretion: basal + cephalic

Answer 9

Basal - follows circadian rhythm. High pm, low am. Not much contribution

Cephalic - smell, sight, taste of food. Contributes 30%. Mediated by Ach + vagus nerve

Question 10

Phases of acid secretion: gastric + intestinal

Answer 10

Gastric - 50-60%. Distension of stomach leads to Ach - Ach + GRP. Partial digestion of proteins leads to gastrin from G cell

Intestinal - 5-10%. Partial digestion of AAs/peptides - stimulates G cells in duodenum to release gastrin

Question 11

Mucosal protection

Answer 11

Mucus layer traps HCO3 to maintain ph of 7

PGs important to increase HCO3 production, decrease acid production and increase mucous production

Question 12

H. pylori

Answer 12

Colonises 40% of stomachs
In antrum, causes G cells to hyper secrete gastrin + D cells to reduce somatostatin so hypergastrinaemia
In body, causes reduced acid + get gastric ulcers as bacteria cause inflammation - IL1B - reduces acid

Have flagella for motility, secrete urease which converts urea into NH4 + HCO3 to neutralise their enviro to survive