CBSE Class 12-science Answered
Why do antihistamines not affect the secretion of acid in stomach?
Receptors are proteins that bind to ligands like hormones and are responsible for mediating the effect of the ligand. For a ligand the different cells have receptors with different characteristics.
Histamine receptors are of 4 different types. H1 receptors are present on air passages, blood vessels while stomach cells express H2 receptors.
The H2 receptor antagonists (H2RA) are a class of drugs used to block the action of histamine on parietal cells (specifically the histamine H2 receptors) in the stomach, decreasing the production of acid by these cells.
The common antihistamines block the binding of histamine to H1 receptors but not H2 receptors and therefore do not affect the secretion of gastric juice.