Which control mechanism will a patient's target cells implement in order to adapt to high hor-mone concentrations?

a. Negative feedback
b. Positive feedback
c. Down-regulation
d. Up-regulation

ANS: C
High concentrations of hormone decrease the number of receptors; this is called down-regulation. Thus, the cell can adjust its sensitivity to the concentration of the signaling hormone. Negative and positive feedbacks regulate hormone release. Up-regulation is a response to low concentra-tions of hormone, thus increasing the number of receptors per cell.