Which of the following acid is secreted in the stomach ?
Hydrochloric acid
The stomach secretes hydrochloric acid — option 4.
Which cells make it. The gastric glands in the stomach lining contain several cell types, and the parietal (oxyntic) cells are the ones that secrete HCl. They pump hydrogen ions into the stomach lumen using the H+/K+ ATPase — the proton pump — against a concentration gradient of about a million to one, which makes it one of the most energy-expensive transport processes in the body.
| Gastric cell | Secretion | Function |
|---|---|---|
| Parietal (oxyntic) | Hydrochloric acid, intrinsic factor | Acidifies the stomach; intrinsic factor allows vitamin B12 absorption |
| Chief (peptic) | Pepsinogen | Converted by acid into pepsin |
| Mucous neck | Mucus, bicarbonate | Protects the wall from the acid |
| G cells | Gastrin | Hormone that stimulates acid secretion |
What the acid does. Gastric juice is held at a pH of roughly 1·5 to 3·5. At that acidity it converts inactive pepsinogen into the active protein-splitting enzyme pepsin, denatures dietary proteins so the enzyme can reach their peptide bonds, kills most ingested bacteria, and helps release iron and calcium from food for absorption.
Why the stomach is not destroyed by it. The mucous neck cells lay down a thick alkaline mucus-bicarbonate layer over the epithelium, and the enzyme is secreted as an inactive precursor so that digestion only begins in the lumen. When this barrier fails — commonly through infection with Helicobacter pylori or long use of NSAIDs — the result is a peptic ulcer, which is why antacids and proton-pump inhibitors such as omeprazole are prescribed.
Why the other options are wrong. Sulphuric and nitric acid are strong mineral acids used in industry and are not produced by any human tissue. Phosphoric acid occurs in the body as phosphate in bone, DNA and ATP, but it is never secreted as a digestive acid.
Hence, the answer is hydrochloric acid.
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