This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
Down-regulation is 
Select and explain. 
A. Increased destruction of a hormone, B. Feed back inhibition of hormone secretion, C. Decreased concentration of a hormone in blood, D. Decrease in number of receptors for a hormone
D: Decrease in number of receptors for a hormone
Answer: D: Decrease in number of receptors for a hormone 
Explanation: Downregulation: An decrease in the number of receptors on the surface of target cells, making the cells less sensitive to a hormone or another agent Downregulation of receptors happens when receptors have been chronically exposed to an excessive amount of hormone Ref : Biochemistry by U. Satyanarayana 3rd edition Pgno : 428