Final answer:
Acetylcholine stimulates endothelial cells to produce Nitric Oxide (NO) by activating Nitric Oxide Synthase (NOS), which causes vasodilation.
Step-by-step explanation:
The correct answer is a. Acetylcholine.
Acetylcholine stimulates endothelial cells to produce Nitric Oxide (NO) by activating Nitric Oxide Synthase (NOS). Nitric oxide acts as a paracrine chemical that causes vasodilation, meaning it relaxes blood vessels and widens their diameter, allowing for increased blood flow. This process is important for regulating blood pressure and maintaining proper circulation throughout the body.
For example, nitroglycerin, a treatment for heart disease, triggers the release of nitric oxide, which causes blood vessels to dilate and restores blood flow to the heart.