Final answer:
Down-regulation results in target cells becoming less sensitive to hormones due to a decrease in receptor numbers, while up-regulation leads to a higher sensitivity through an increase in hormone receptors.
Step-by-step explanation:
Down-regulation makes a target cell less sensitive to a hormone while up-regulation makes a target cell more sensitive to a hormone.
Hormones mediate changes in target cells by binding to specific hormone receptors. The sensitivity of a cell to a hormone is partly determined by the number of receptors on the cell's surface that the hormone can bind to. When there is an increase in hormone levels, down-regulation can occur, which means there is a decrease in the number of receptors on the target cell. This makes the cell less sensitive to the hormone, reducing cellular activity.
Conversely, during up-regulation, the number of receptors on the cell's surface increases in response to a decrease in hormone levels or other regulatory signals, thus making the cell more sensitive to the hormone. This leads to an increase in the cellular response and activity. Therefore, cells can adjust their sensitivity to hormones through these mechanisms, maintaining homeostasis in response to varying levels of hormonal signals.