Stomach pH Regulation, Antacids, Hydrogen Receptor Antagonists, Active Metabolites, Buffers

Question 1

How is pH regulated in the stomach?

For what reason is the pH so low?

What happens when there is an excess of these acidic secretions?

Answer 1

pH stomach is between 1-2 from the production of HCL by parietal cells in the stomach

the acidic environment is not tolerated by microorganisms (bacteria) that enter with food (defence)

the digestive enzymes in the stomach (pepsin, which breaks down proteins) require a low pH for optimum catalytic activity

excess gastric juice: caused by excess alcohol, smoking, caffeine, stress, some anti-inflammatory drugs

can lead to acid indigestion, heartburn/acid reflux, ulceration (dmg to the lining of the gut wall)

dyspepsia: feelings of pain and discomfort in the upper abdomen, including indigestion and heartburn

Question 2

What can help treat dyspepsia?

Answer 2

antacids: weakly basic compounds that neutralize acids allow repair of the mucous layer, neutralization of the acid prevents further erosion of the gut lining to allow ulcers to heal

Most common antacids are metal hydroxides, carbonates, sodium hydrogen carbonates

1) calcium hydroxide
Ca(OH)2 + 2HCl -> CaCl2 + 2H2O

2) magnesium hydroxide

3) aluminum hydroxide
Al(OH)3 + 3HCl -> AlCl3 + 3H2O

4) sodium hydrogen carbonate
NaHCO3 + HCl -> NaCl + H2O + CO2

5) calcium carbonate
CaCO3 + 2HCl -> CaCl2 + H2O + CO2

Question 3

What are the side effects of antacids?

Answer 3

gas released can cause boating, reduced by antifoaming agents that are added to the formulation

some antacids contain alginate which out to the top of the stomach forming a raft, a barrier preventing reflux into the esophagus

Question 4

What is histamine?

Answer 4

histamine for different functions in the body and several different receptor sites. in the stomach it stimulates the secretion of stomach acid by interacting with H2 receptors (not hydrogen) in the parietal cells in the gastric glands

many complex mechanisms ensure that gastric juice is only released when required

Question 5

What competes with histamine?

Answer 5

H2-receptor antagonists; compete with histamine for the binding at H2 receptors

Question 6

What is the last step of gastric acid secretion?

Answer 6

parietal cells pump protons across their membranes into the lumen of the stomach

for one H+ pumped into the lumen, one K+ ions pumped out (no charge build-up)

movement of the ions occurs against their concentration gradient, and requires energy, provided by the hydrolysis of an energy carrier ATP, using the enzyme ATPase, or H+/K+ ATPase, or gastric proton pump