Final answer:
The statement that every hormone has a specific receptor is true. Hormones affect cells through specific hormone receptors which can be on the cell surface or intracellular, and the presence and number of these receptors regulate the cell's response to the hormone.
Step-by-step explanation:
The statement that every hormone has a specific receptor that causes an action for that cell is true. Hormones function by binding to specific hormone receptors, which can be located on the cell’s surface or within its interior. The hormone-receptor interaction triggers various changes within the cell. In fact, a particular hormone will only affect a cell if that cell has the receptors that can bind to the hormone. Receptors can be widespread or limited to specific types of cells. For instance, thyroid hormones have receptors on many different tissues and are responsible for increasing the whole body's metabolic activity.
The number of receptors on a cell's surface can fluctuate, leading to changes in the cell's sensitivity to a hormone. This is known as up-regulation or down-regulation. Up-regulation involves an increase in receptor numbers, enhancing the cell's response to a hormone, whereas down-regulation decreases the number of receptors, dampening the cellular response. The specificity and sensitivity of cells to hormones are critical for maintaining balanced physiological processes.