D4

Question 1

Condition and cause

Answer 1

Acid indigestion - discomfort in stomach
Heartburn - acid rising into oesophagus
Ulcers - damage to stomach lining and inflammation
Caused when excess hydrochloric acid is produced by gastric glands in walls of stomach, making gastric juice too acidic
Acid is needed to kill any bacteria in food ingested, provide optimum pH environment for digestive enzymes which act in stomach (pepsins)

Question 2

H2 receptor antagonists

Answer 2

Bind histamine in the parietal cells and stimulate stomach acid secretion
Histamines have a number of roles - mainly allergy response
H2 receptor antagonists block the action of histamines on the parietal cell receptors
Ranitidine is an example and it inhibits stomach acid production - delivered orally and is generally formulated as a hydrochloride salt

Question 3

Proton pump inhibitors

Answer 3

e.g. omeprazole and esomeprazole
Release of H+ ions from the parietal cells of stomach to lumen is final stage of acid secretion
As H+ is pumped out of cell, K+ is taken in across membrane to maintain charge within cell - requires energy as it works against proton gradients
These drugs block the proton pump, preventing the release of acid in the stomach

Question 4

Mode of action for H2 antagonists and proton pump inhibitors

Answer 4

Question 5

Antacids

Answer 5

typically weak bases used to neutralise excess hydrochloric acid and relieve the associated pain
commonly used ingredients: aluminium hydroxide (most effective as it has 3 -OH groups), magnesium hydroxide, magnesium carbonate, sodium hydrogen carbonate
Sodium hydroxide and potassium hydroxide not used as antacids because they are strong alkalis and too corrosive to body tissue

Question 6

Neutralisation reactants

Answer 6

Question 7

Alginates and antifoaming agents

Answer 7

alginates help prevent heartburn by producing a neutralising layer (Raft) on top of the stomach contents - prevents acid in stomach from rising into the oesophagus and causing heartburn
Antacids that contain carbonates will also contain anti-foaming agents such as dimethicone (reduces bloating of the stomach as a result of CO2 production)

Question 8

Interactions with other medications

Answer 8

Change in pH of stomach due to use of antacids can interfere with other reactions that occur in stomach
Can alter digestive behaviour of patients
Absorption and effectiveness of other medications can also be altered

Question 9

pH and buffering

Answer 9

Small changes in pH can have large impact on biological system
Key way biological systems are protected from pH fluctuations is through buffers - resist small changes in pH as a result of the addition of a small amount of strong acid or base
Buffer - made from solution of weak acid and salt of its conjugate base

Question 10

Buffer equilibrium

Answer 10

For a buffer, pH is dependent on the interactions of components
2 systems present - weak acid equilibrium (HA(aq) ⇌ H+(aq) + A-(aq)) and salt (MA (aq) ⇌ M+ (aq) + A- (aq))

Question 11

Acid buffer action

Answer 11

When acid is added, pH initially decreases due to addition of H+
According to Le Chatelier’s principle, the extra H+ will react with A-, therefore reducing H+ again and raising pH to original value
When base is added, pH initially increases as the OH- reacts with H+ in solution
Due to Le Chatelier’s principle, weak acid will dissociate to increase H+ again and lower pH to original value

Question 12

Henderson-Hasselbach equations

Answer 12

Provided in Section 1 data booklet
possible to determine pH of a buffer solution as long as Ka or Kb component acid or base and the ratio of initial concentrations of acid and salt used to prepare buffer are known