The short-term controls of blood pressure, mediated by the nervous system and bloodborne chemicals, primarily operate via all but which of the following?

• A. reflex arcs involving baroreceptors
• B. baroreceptor reflexes
• C. autonomic neural pathways
• D. hormonal modulation by adrenaline and other factors

Answer: (A)

Short-term blood pressure control relies on fast neural reflexes and circulating chemicals that change heart rate, contractility, and vascular tone. Baroreceptors in the carotid sinus and aortic arch detect pressure and trigger baroreceptor reflexes that quickly adjust sympathetic and parasympathetic outflow to the heart and vessels. The autonomic neural pathways are the channels that carry these rapid signals to the heart and vessels, producing immediate changes in cardiac output and peripheral resistance. Hormonal modulation, especially adrenaline and other catecholamines, provides an additional quick means to tweak heart rate, contractility, and vascular tone during short-term fluctuations. The first option names reflex arcs involving baroreceptors, which is essentially the same mechanism as the second option (baroreceptor reflexes) and isn’t a distinct pathway. Because it isn’t describing a separate mechanism, it’s the one that doesn’t add a new category of short-term control.