What happens during down regulation of receptors?

• A. Decrease in receptor sensitivity
• B. Decrease in receptor numbers
• C. Increase in receptor numbers
• D. Increase in ligand production

Answer: (B)

During down regulation of receptors, there is a decrease in receptor numbers on the surface of the cell. This process typically occurs in response to prolonged exposure to high levels of a ligand, such as a hormone or neurotransmitter. When the ligand binds to the receptors, the cellular response may become less effective over time due to an oversaturation of signals. To maintain homeostasis and prevent overstimulation, the cell responds by internalizing or degrading some of the receptors, leading to a reduced number of receptors available for ligand binding.

This mechanism serves as a protective adaptation, helping the cell to avoid excessive signaling and maintain proper physiological function. For example, in the case of insulin, prolonged high levels of insulin can result in a decrease in insulin receptors on cell surfaces, contributing to insulin resistance. Understanding this concept is crucial as it highlights how cells regulate their sensitivity in response to changing environments and signaling molecules.