Final answer:
Hormone receptor molecules can be up-regulated or down-regulated to alter a target cell's sensitivity to hormones, which in turn affects cellular activity and responsiveness to hormonal signals.
Step-by-step explanation:
Hormone receptor molecules may be up-regulated or down-regulated in order to change the target cell's sensitivity to a given hormone. This process affects cellular activity by modifying how responsive a cell is to hormonal signals. Up-regulation increases the number of receptors in response to rising hormone levels, making cells more sensitive to the hormone. Conversely, down-regulation decreases the number of receptors when hormone levels are high, which reduces the cell's sensitivity and activity. Receptor binding, whether to intracellular hormone receptors affecting gene transcription or to cell surface receptors stimulating signaling pathways, is crucial for normal body processes.
Cells can change their sensitivity to a given hormone by modifying the number of hormone receptor molecules present. This is known as receptor modulation. Receptor modulation can occur through up-regulation, where the number of receptors increases in response to rising hormone levels, or through down-regulation, where the number of receptors decreases in response to rising hormone levels. For example, if there is an increase in thyroid hormone levels, target cells may up-regulate their thyroid hormone receptors to become more sensitive to the hormone and increase cellular activity.