Baroreceptors are stretch-sensitive mechanoreceptors that detect changes in blood pressure. Which statement about baroreceptors is true?

• A. Baroreceptors are located in venous valves
• B. They respond to osmotic changes
• C. They sense chemical composition of blood
• D. They are located in arterial walls and sense stretch

Answer: (D)

Baroreceptors monitor how stretched the arterial walls are, not the chemical content of the blood. They sit in the walls of major arteries, notably the carotid sinus and the aortic arch. When blood pressure rises, the increased stretch makes them fire more rapidly, signaling the brainstem to boost parasympathetic output and reduce sympathetic tone, which slows the heart and dilates vessels to bring blood pressure down. When pressure falls, their firing reduces, leading to increased sympathetic activity to raise heart rate and constrict vessels. The other statements are not correct because baroreceptors are not located in venous valves, they do not primarily respond to osmotic changes, and they do not sense the chemical composition of blood (that role belongs to osmoreceptors and chemoreceptors, respectively).