GUT- Gastric Acid Secretion: Regulation

Question 1

describe the contents of gastric acid

Answer 1

Cations: Na+,K+,MG2+, H+
Anions: Cl-, HPO4-, SO4-
pepsins, lipases, mucus, intrinsic factor

Question 2

What is the pH of the stomach

Answer 2

3.0

Question 3

what type of cells is the body of the stomach lined with

Answer 3

epithelial cells with tubular glands which are lined with parietal cells

Question 4

what do the parietal cells secrete

Answer 4

HCl and intrinsic factor

Question 5

what substance is mainly secreted in the antrum of the stomach

Answer 5

gastrin (HCl still secreted but gastrin secretion increased)

Question 6

what are the exocrine secretions of the stomach

Answer 6

mucus, acid, pepsinogen

Question 7

what do enterochromaffin-like cells secrete (ECL cells)

Answer 7

paracrine agents e.g., histamine

Question 8

which cells secrete HCl

Answer 8

parietal cells

Question 9

how is gastric acid produced in the stomach lumen

Answer 9

water and carbon dioxide combine in the parietal cell cytoplasm to produce carbonic acid- catalysed by carbonic anhydrase

carbonic acid then disassociates into a hydrogen ion and bicarbonate ion

the hydrogen ion is transported into the stomach lumen via H+-K+ ATPase ion pump

bicarbonate is the transported out of the cell and into the blood in exchange for a Cl- ion

the Cl- ion is then transported into the stomach lumen

this means there are many H+ and Cl- ions in the stomach lumen which (due to their opposite charges_ combine to form HCL

Question 10

what are the three phases of gastric secretion

Answer 10

Cephalic phase
gastric phase
intestinal phase

Question 11

what is the purpose of mucus secretion in the stomach

Answer 11

mucus is alkaline, thick and sticky- increases bicarbonate; forms a water insoluble gel on the epithelial cells which protects against HCl

Question 12

what does rennin do?

Answer 12

curdles milk into caesin clot

Question 13

what do lipases do

Answer 13

breakdown fatty acids and glycerol

Question 14

what is the function of intrinsic factor

Answer 14

absorption of vitamin B12

Question 15

what is the purpose of HCl in the stomach

Answer 15

kills bacteria, aids in denaturation of digested food activates pepsinogen (protein digestion)

Question 16

what is the cephalic phase

Answer 16

first phase of digestion - seeing food, smelling food, chewing food - promotes the excretion of ACh and Gastrin

Question 17

how is gastric acid production increased in the stomach

Answer 17

ACh stimulation of parietal cells via release from the vagus nerve - cephalic phase
ACh release via vagus nerve on detection of distension of the stomach - gastric phase

gastrin secretion from G cells in the stomach which are activated by the vagus nerve. Gastrin binds to CCK receptors on the parietal cells which elevates calcium levels causing increases vesicular fusion and increased acid secretion

ECL cells in the stomach secrete histamine which binds to H2 receptors on the parietal cells. this happens as a result of the presence pf gastrin and ACh

Question 18

what is the gastric phase

Answer 18

distension of stomach, increase in peptide concnetration - promotes the secretion of ACh and Gastrin

Question 19

what is the intestinal phase

Answer 19

balances the secretory activity of the stomach and the digestive and absorptive capacities of the small intestine

Question 20

what occurs during the intestinal phase

Answer 20

high acidity of duodenal contents reflexively inhibits acid secretion (to prevent chyme from becoming too acidic)

increase in acidity will inhibit the activity of digestive enzymes, bicarbonate and bile salts

distension of the duodenum, hypertonic solution, amino acids, fatty acids and monosaccharides all inhibit acid secretion

Question 21

How is gastric acid production decreased

Answer 21

accumulation of acid in an empty stomach between meals - leads to a lower stomach pH which inhibits secretion of gastrin by the production of somatostatin from D cells

enterogastric reflex in the duodenum

presence of chyme in duodenum stimulates entero-endocrine cells to release cholecystokinin and secretin which inhibits gastric acid secretion

other hormones including GIP (glucose dependent insulinotropic peptide) and VIP (Vasoactive intestinal polypeptide) decrease acid production

Question 22

what are stimulants of HCl secretion

Answer 22

histamine, ACh, gastrin, caffine, alcohol, NSAIDS, nicotine, H.Pylori, genetics, stress

Question 23

why and how is pepsin secreted

Answer 23

secreted by chief cells in the form of pepsinogen - activated if the concentration of H+ is high

acidity alters the shape which exposes the active site

known as an autocatalytic feedback process

inactivated when food enters the small intestine (bicarbonate and peptides neutralise the H+ ions)