Which stimulus do osmoreceptors primarily respond to?

Which stimulus do osmoreceptors primarily respond to?

• A. Solute concentrations of body fluids.
• B. Temperature changes.
• C. Light intensity.
• D. Mechanical pressure.

Answer: (A)

Osmoreceptors monitor the osmolarity of body fluids—the solute concentration in extracellular fluid. When osmolarity rises, water moves out of the osmoreceptor cells by osmosis, causing them to shrink and increase their activity. This signals the brain to induce thirst and to release antidiuretic hormone (ADH), promoting water retention and helping restore normal osmolar balance. They’re not primarily responding to temperature, light, or mechanical pressure—the other options correspond to thermoreceptors, photoreceptors, and mechanoreceptors/baroreceptors, respectively.

Osmoreceptors monitor the osmolarity of body fluids—the solute concentration in extracellular fluid. When osmolarity rises, water moves out of the osmoreceptor cells by osmosis, causing them to shrink and increase their activity. This signals the brain to induce thirst and to release antidiuretic hormone (ADH), promoting water retention and helping restore normal osmolar balance. They’re not primarily responding to temperature, light, or mechanical pressure—the other options correspond to thermoreceptors, photoreceptors, and mechanoreceptors/baroreceptors, respectively.