Final answer:
The process that causes a reduction in receptor numbers when hormone levels are high is called downregulation. This mechanism reduces cell sensitivity to the hormone and maintains homeostasis.
Step-by-step explanation:
When there are elevated hormone levels, the process that triggers a reduction in the number of receptors is known as downregulation. This feedback mechanism helps to maintain homeostasis by reducing a cell’s sensitivity to a specific hormone when it is in excess. In contrast, upregulation occurs when hormone levels are chronically reduced, leading cells to increase their number of receptors, thus becoming more sensitive to the hormone present. Downregulation helps cells become less reactive to excessive hormone levels, while upregulation makes them more reactive to hormones when they are scarce.