Final answer:
Acetylcholine primarily stimulates the secretion of digestive enzymes in the GI tract, as part of the 'rest-and-digest' response of the parasympathetic nervous system.
Step-by-step explanation:
The effect of acetylcholine on the GI tract relates to its role in the autonomic nervous system, specifically in the parasympathetic division, which is often called the 'rest-and-digest' system. Acetylcholine, when released, tends to increase GI secretion and motility. It stimulates neurons of the enteric nervous system, which lead to enhanced digestion processes.
Regarding the options provided:
- (a) Inhibition of peristalsis - This is not correct; acetylcholine generally promotes peristalsis.
- (b) Constriction of sphincters - While acetylcholine can affect sphincters, this is not its primary role in the digestive process.
- (strong)>(c) Stimulation of digestive enzymes - This is the correct effect of acetylcholine on the GI tract.
- (d) Relaxation of smooth muscles - This is not the main effect, as acetylcholine usually has a stimulatory effect on smooth muscle contraction in the GI tract.
Therefore, the correct answer is (c) Stimulation of digestive enzymes, which aids in the digestion of food.