D.4 (PART 1): pH REGULATION OF THE STOMACH
UNDERSTANDINGS
- Non-specific reactions, such as the use of antacids, are those that work to reduce excess ______________ acid.
- Active metabolites are the active forms of a drug after it has been processed by the body.
APPLICATION AND SKILLS
- Explanation of how excess acidity in the stomach can be reduced by the use of different bases.
- Construction and balancing of equations for neutralization reactions and the stoichiometric application of these equations.
- Solving buffer problems using the Henderson-Hasselbalch equation.
- Explanation of how compounds such as ranitidine (Zantac) can be used to inhibit stomach acid production.
- Explanation of how compounds like omeprazole (Prilosec) and esomeprazole (Nexium) can be used to suppress acid secretion in
the stomach.
NATURE OF SCIENCE
- Collecting data through sampling and trialing – one of the symptoms of dyspepsia is the overproduction of stomach acid. Medical
treatment of this condition often includes the prescription of antacids to instantly neutralize the acid, or H2-receptor antagonists or
proton pump inhibitors which prevent the production of stomach acid.
INTRO: STOMACH ACID / GASTRIC JUICE
- Digestive fluid/gastric juice is secreted by cells in the stomach lining.
*COMPONENTS OF GASTRIC JUICE / DIGESTIVE FLUID:
COMPONENT
FUNCTION
- denatures ______________ (acid itself does not break down food molecules)
Hydrochloric acid (HCl)
- provides optimum ____ (1.0 to 2.5) for pepsin and other enzymes in gastric juice
- _________________(kills harmful microorganisms digested with food)
- breakdown ___________________into peptides and individual amino acids
Enzymes (pepsins)
- ________________ the acid
Hydrogencarbonate ions
- prevent acid from digesting ___________ tissues
(HCO3-)
- _______________ the acid
Mucous
- prevent acid from digesting _______________ tissues
- breakdown of stomach’s mucous lining results in painful _________________
- solvent
Water
Salts (mostly KCl and NaCl)
1. ANTACIDS
- An antacid is a ____________ that neutralizes excess stomach acid (i.e. ___________) in order to adjust the stomach pH to the
desired level.
- Examples of antacids include metal oxides, hydroxides, carbonates or hydrogen-carbonates.
*SPECIFIC EXAMPLES - COMPLETE THE FOLLOWING:
HCl(aq) 
1. Magnesium oxide:
MgO(s) +
2. Magnesium hydroxide
Mg(OH)2(aq) + HCl(aq) 
3. Aluminum hydroxide
Al(OH)3(s) +
4. Calcium carbonate
CaCO3(s) +
5. Sodium hydrogen carbonate
NaHCO3(aq) + HCl(aq) 
HCl(aq) 
HCl(aq) 
*SAMPLE PROBLEMS (TITRATION / NEUTRALIZATION STOICH.)
1. Hypochlorhydria is a health condition caused by insufficient production of gastric acid. A 20.0 cm 3 sample of gastric juice with a
density of 1.03 g cm-3 was taken from a patient suffering from Hypochlorhydria and titrated with a
0.0215 mol dm-3 solution of sodium hydroxide to pH = 7.0. The volume of the titrant used was 1.47 cm 3. Calculate:
a) the molar concentration of hydrogen chloride in the sample
b) the pH of the sample, to two significant figures
c) the mass percentage of hydrogen chloride in the sample.
2. Which would be most effective in combating indigestion – a spoonful of liquid containing 1.00 g of magnesium hydroxide or a
spoonful of liquid containing 1.00 g of aluminum hydroxide?
2. INHIBITION OF STOMACH ACID PRODUCTION
*ULCER  results when protective mucous lining of stomach is damaged due to the production of excess stomach acid
SUMMARY OF DRUGS THAT INHIBIT STOMACH ACID PRODUCTION:
DRUG
-Ranitidine (ZANTAC)
MODE OF ACTION
- blocks the action of ____________________
*HISTAMINE - released by certain cells in the stomach
- stimulates other cells in the stomach to release ______________
- interact with a cysteine residue in the H+ / ATPase enzyme (the ‘proton pump) chemical
system
- this __________________ the ability of these cells to secrete ________________
*PPIs
[e.g. **Omeprazole (PRILOSEC)
and Esomeprazole (NEXIUM)
*PPI = proton pump inhibitor
**The formula of omeprazole is given in section 37 of the IB data booklet
N.B.
- Omeprazole (inactive) and Esomeprazole (active) are a pair of ____________________.
- Omeprazole (Prilosec) actually consists of a _________________ mixture of the two isomers and undergoes a chiral shift in the
body that converts the inactive enantiomer into the active enantiomer.
3. SIDE EFFECTS
- Side effects may result from the drugs themselves or by active metabolites – the active form of the drug after it has been processed
by the body.
- e.g. Belching to release gas is a common side-effect associated with most antacids.
SUMMARY OF COMMON SIDE EFFECTS
ANTACID
Magnesium-containing
Aluminum-containing
Zantac
PPIs (e.g. Nexium)
SIDE EFFECT(S)
- diarrhea
- constipation
- diarrhea
- headache
- dizziness
SHORT-TERM
- diarrhea
- headache
- dizziness
LONG-TERM
- ↑ risk of ________________
- ↑ risk of developing food and
drug ________________