What changes are expected when carotid sinus is digitally compressed?
**Core Concept**
The carotid sinus is a baroreceptor located at the bifurcation of the common carotid artery, responsible for detecting changes in arterial blood pressure. It plays a crucial role in regulating heart rate and blood pressure through the carotid sinus reflex.
**Why the Correct Answer is Right**
When the carotid sinus is digitally compressed, it activates the baroreceptors, leading to an increase in the afferent nerve impulses to the brain. This triggers the carotid sinus reflex, resulting in a decrease in heart rate (negative chronotropic effect) and a decrease in force of contraction (negative inotropic effect). The carotid sinus reflex also causes vasodilation of the blood vessels, leading to a decrease in blood pressure. This response is mediated by the vagus nerve, which releases acetylcholine, and the sympathetic nervous system, which releases noradrenaline.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because compression of the carotid sinus would not lead to an increase in heart rate. The carotid sinus reflex is a baroreceptor-mediated response that decreases heart rate.
* **Option B:** This option is incorrect because the carotid sinus reflex does not cause vasoconstriction. Instead, it leads to vasodilation, which decreases blood pressure.
* **Option D:** This option is incorrect because the carotid sinus reflex does not cause an increase in blood pressure. In fact, it leads to a decrease in blood pressure through vasodilation.
**Clinical Pearl / High-Yield Fact**
The carotid sinus reflex is a vital mechanism that helps regulate blood pressure and heart rate. It is often tested in clinical exams, and knowledge of its effects on heart rate and blood pressure is essential for postgraduate medical students.
**Correct Answer:** C. Decrease in heart rate and force of contraction, with vasodilation.