4. pH regulation of the stomach

Question 1

Antacids

Answer 1

Antacids reduce excess stomach acid by neutralization.

HCl in stomach kills bacteria and provides optimum pH
Excess HCl causes acid indigestion, heartburn and ulcers

Question 2

Antacid Equations

Answer 2

Must be a weak base (strong are harmful)

CaOH2 + 2HCl => CaCl2 + 2H2O

MgOH2 + 2HCl => MgCl2 + 2H2O

AlOH3 + 3HCl => AlCl3 + 3H2O

Na2CO3 + 2HCl => 2NaCl + CO2 + H2O

NaHCO3 + HCl => NaCl + CO2 + H2O

Question 3

Antacid additives

Answer 3

Alginates
- Creates a neutralising layer
- Prevents acid rising into the oesophagus

Dimethicone (anti-foaming agent)
- Prevents bloating and flatulence

Question 4

Stomach acid Inhibitors

Answer 4

Relieve acid reflux, heartburn and indigestion

1) Proton Pump Inhibitors (PPI)
2) H2 Receptor Antagonists / Blocker

PPIs inhibit whilst Antacids neutralise.
PPIs have a much longer lasting effect than antacids.

Question 5

Proton Pump Inhibitors (PPI)

Answer 5

Omeprazole

Gastric Proton Pumps pump H+ in the stomach
PPI Inhibits the pump, and prevents release of the protons.

Longer lasting effect (3 days)
They’re used to treat stomach ulcers and provide relief from symptoms of acid reflux

Question 6

H2 Receptor Antagonists / Blocker

Answer 6

Ranitidine

Histamine stimulates secretion of stomach acid by interacting with H2 receptors in the lining of the stomach
H2 blockers compete with histamine to bind with the receptors, blocking histamine.
H2 receptor antagonist example: Ranitidine

Question 7

Calculating pH of buffer solutions

Answer 7

Hendersson-Hasselbalch equation

pH = pKa + log10 ([A-] / [HA])

Where [A-] = initial concentration of the salt
Where [HA] = initial concentration of the weak acid.

Question 8

Assumptions of the Hendersson-Hasselbalch equation

Answer 8

1st assumption
Weak acids only partially dissociate and not much, so it’s assumed that the [HA]initial = [HA]final

2nd assumption
Salt fully dissociates within the solution so that initial [A-] concentration is the same as [AB]