Down-regulation refers to which of the following changes in receptor numbers?

Down-regulation refers to which of the following changes in receptor numbers?

• A. The increase in number of receptors
• B. No change in receptor numbers
• C. Desensitization
• D. The decrease in number of receptors

Answer: (D)

Down-regulation is when a cell reduces the number of receptors on its surface in response to persistent stimulation by a ligand. With ongoing exposure, receptors are often internalized and degraded or their production is decreased, so fewer receptors are available to respond. This lowers the cell’s overall responsiveness to the same level of signaling molecule, contributing to tolerance. The option describing an increase in receptors would be up-regulation, not down-regulation. No change doesn’t fit because this question is about changes in receptor density. Desensitization refers to a diminished response that can happen without changing receptor numbers (through receptor uncoupling or phosphorylation), whereas down-regulation specifically describes a decrease in receptor quantity.

Down-regulation is when a cell reduces the number of receptors on its surface in response to persistent stimulation by a ligand. With ongoing exposure, receptors are often internalized and degraded or their production is decreased, so fewer receptors are available to respond. This lowers the cell’s overall responsiveness to the same level of signaling molecule, contributing to tolerance. The option describing an increase in receptors would be up-regulation, not down-regulation. No change doesn’t fit because this question is about changes in receptor density. Desensitization refers to a diminished response that can happen without changing receptor numbers (through receptor uncoupling or phosphorylation), whereas down-regulation specifically describes a decrease in receptor quantity.