This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: GIT, Subject name: Surgery
Serotonin (5-HT) is one of several mediators of the signs and symptoms of carcinoid tumor. When released from this neoplasm, most of the manifestations of 5-HT are the result of activation of the 5-HT2 receptor. These manifestations are therefore likely to include which of the following effects? 
Select and explain. 
A. Bronchospasm, B. Constipation, C. Skeletal muscle weakness, D. Tachycardia
A: Bronchospasm
Answer: A: Bronchospasm 
Explanation: - 5-HT2 receptors mediate smooth muscle contraction and thus cause bronchospasm and diarrhea, not constipation.- Skeletal muscle and cardiac muscle are relatively insensitive to 5-HT.- Peptic ulceration is not mediated in pa by 5-HT; the autacoid actually reduces acid secretion.