Final answer:
Nitric oxide (NO) causes blood vessels to dilate by causing the relaxation of smooth muscle cells in the vessel walls, leading to increased blood flow. This mechanism is crucial for regulating blood pressure and is also utilized in medications for heart conditions and erectile dysfunction.
Step-by-step explanation:
Nitric oxide (NO) causes blood vessels to dilate due to its interaction with smooth muscle cells in the walls of the blood vessels. Specifically, NO causes these smooth muscle cells to relax, which results in the widening of the blood vessel's lumen, allowing more blood to flow through. This process is a part of the body's regulation of blood pressure and local blood flow. When drugs like nitroglycerin are used, they release NO, which can restore blood flow to areas like the heart. This same pathway is manipulated by erectile dysfunction medications, such as Viagra, which inhibit the enzyme phosphodiesterase type 5 (PDE5) and increase levels of cyclic GMP (cGMP), further promoting vasodilation and blood flow.