Gastric secretion

Question 1

Regulation of acid secretion

• parasympathetic
• gastrin
• histamine
• somatostaton
• secretin/CCK

Answer 1

Parasympathetic
-via X => Ach release in cephalic/gastric onto ECL

Gastrin

• via G cells => bind to CCK rec on ECL => histamine release
• binds to CCK rec on parietal cells => increased vesicular fusion
• acts on chief cells => increased pepsinogen secretion

Histamine
-via Ach/gastrin acting on ECL => binds to H2 rec on parietal cell => increased vesicular fusion

Somatostatin
-via D cells/low pH => inhibits gastrin prod

Secretin/CCK
-via S and I cells => inhibits acid sec

Question 2

Describe how parietal cells change in order to release acid

Answer 2

Most HKATPases in tubulovesicles in parietal cells
When stimulated => increased fusion of vesicles with membrane => increased acid and IF prod

Carbonic anhydrase => H and HCO3
HKATPase exchange => H release into stomach
HCO3Cl exchange => HCO3 release into interstitium
Cl channel => Cl release into stomach
H + Cl => HCl

Question 3

Function of HCL

Answer 3

Activates pepsinogen released from chief cells

Kills pathogens

Question 4

Name 2 drugs that you would use to treat a peptic ulcer and their mechanisms

Answer 4

Omeprazole
-irreversible HKATPase inhibitor

Famotidine
-H2 rec antagonist => reduced histamine production

Question 5

Name the 5 main cells in the gastric pit

Answer 5

Parietal
-HCL/IF prod

Endocrine
-Gastrin

Stem
-Replace cells

Chief
-Pepsinogen

Mucus
-HCO3/mucus secretion

Question 6

Describe the cephalic phase of digestion

Answer 6

Sight/thought/smell/taste of food => vagus => increased secretions

Conditioned reflex, only occurs with food we like

Question 7

Describe the gastric phase of digestion

Answer 7

Stomach stretches => increased Ach, pH => increased gastrin => increased HCl and SM contractions

Question 8

Describe the intestinal phase of digestion

Answer 8

Duodenal chyme initially causes intestinal gastrin release => brief stimulation

Intestinal distention and fatty chyme => inhibits secretions

Question 9

Describe the

• parasympathetic
• prostaglandin involvement in mucus secretion regulation

Answer 9

Parasympathetic
-via X => Ach onto mucus cells

Prostaglandins

• stimulates mucus and HCO3 secretion
• increases mucosal blood flow

Question 10

Describe the importance of mucus

How does it work

Answer 10

Protects stomach wall from acid and enzymes
Produces HCO3 rich barrier (pH7)

Carbonic anhydrase => H + HCO3
HCO3 exchanged for Cl

Question 11

What causes peptic ulcers

Answer 11

NSAIDs, increased acid, Helicobacter Pylori => breached mucus barrier
HCl and enzymes act on epithelium => ulcer forms => cell death