Final answer:
Serotonin has a vasodilatory effect primarily in the blood vessels of skeletal muscles, particularly in the lower limbs, and also affects the vessels of the brain, promoting an increase in blood flow in these areas.
Step-by-step explanation:
Serotonin (5-hydroxytryptamine or 5-HT) is known to be a crucial neurotransmitter in the central nervous system. However, it also plays a significant role outside of the nervous system, particularly in the cardiovascular system. Serotonin has a vasodilatory effect on blood vessels in several areas of the body, including the skeletal muscles, especially in the lower limbs, which dilate in response to specific stimuli such as the fight-or-flight response.
This vasodilation allows for an increase in blood flow to the active skeletal muscles. Additionally, serotonin induces vasodilation in the vessels of the brain and enhances vascular permeability in general. Furthermore, serotonin can stimulate smooth muscle contraction and is involved in the regulation of vascular tone.