True about cephalic phase of gastric acid secretion-
**Core Concept**
The cephalic phase of gastric acid secretion refers to the initial phase of gastric acid release in response to the sight, smell, and thought of food, which is mediated by the vagus nerve and the release of neurotransmitters such as acetylcholine.
**Why the Correct Answer is Right**
The cephalic phase is triggered by the anticipation of food, which stimulates the vagus nerve to release acetylcholine, a neurotransmitter that binds to muscarinic receptors on parietal cells in the stomach, leading to the release of gastric acid. This phase is responsible for approximately 20-30% of total gastric acid secretion. The cephalic phase is an example of a conditioned reflex, where the brain associates certain stimuli (such as the sight or smell of food) with the anticipation of eating, leading to the release of gastric acid.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the role of the vagus nerve in the cephalic phase of gastric acid secretion.
**Option B:** This option is incorrect because it implies that the cephalic phase is solely responsible for gastric acid secretion, when in fact it is only one of three phases.
**Option C:** This option is incorrect because it does not accurately describe the mechanism of action of the cephalic phase.
**Clinical Pearl / High-Yield Fact**
The cephalic phase of gastric acid secretion is an important example of the brain-gut axis, where the central nervous system influences the functioning of the gastrointestinal tract.
**Correct Answer: C.** The cephalic phase of gastric acid secretion is mediated by the vagus nerve and the release of acetylcholine.