Coronary vasodilatation is caused by:
**Core Concept**
Coronary vasodilatation refers to the widening of the coronary arteries, which supply blood to the heart muscle. This process is crucial for maintaining a stable blood flow to the heart, especially during periods of increased demand or stress.
**Why the Correct Answer is Right**
Coronary vasodilatation is primarily mediated by the endothelium-derived relaxing factor, nitric oxide (NO). NO activates guanylyl cyclase in the smooth muscle cells of the coronary arteries, leading to an increase in cyclic guanosine monophosphate (cGMP) levels. This results in the relaxation of smooth muscle cells, causing the coronary arteries to dilate. Additionally, adenosine, a potent vasodilator, plays a significant role in coronary vasodilatation, particularly during periods of ischemia or increased metabolic demand.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a known mediator of coronary vasodilatation.
**Option B:** This option is incorrect because it is a term related to the regulation of blood pressure, not coronary vasodilatation.
**Option C:** This option is incorrect because it is a term related to the regulation of cardiac contractility, not coronary vasodilatation.
**Clinical Pearl / High-Yield Fact**
The endothelium plays a crucial role in maintaining coronary vasodilatation, and dysfunction of the endothelium is a key feature of atherosclerosis and coronary artery disease.
**Correct Answer:** A. Nitric oxide (NO)