Final answer:
Down-regulation is the process of decreasing receptor numbers in response to high hormone levels, which reduces cellular sensitivity and activity as a means to maintain balanced bodily functions.
Step-by-step explanation:
Down-regulation is a biological process where there is a decrease in the number of receptors on target cells, which occurs in response to an increase in hormone levels. This mechanism serves to dampen the cell's response to excessive amounts of the hormone, thereby helping to maintain homeostasis within the body. The presence of an elevated hormone concentration can cause cells to reduce their receptor numbers, making them less sensitive to the hormone and thus decreasing cellular activity.
Conversely, when hormone levels are low, cells may undergo up-regulation, where the number of hormone receptors increases, making the cells more sensitive to the hormone that is present. This sensitivity adjustment is crucial in the body's ability to respond appropriately to varying hormone levels and is an example of negative feedback control in endocrine systems.