Which of the following would cause vasodilation of arterioles?
a. increased activity of the parasympathetic nervous system
b. decreased activity of the parasympathetic nervous system
c. increased activity of the sympathetic nervous system
d. decreased activity of the sympathetic nervous system
The Correct Answer and Explanation is :
The correct answer is:
d. decreased activity of the sympathetic nervous system
Explanation:
Vasodilation refers to the widening of blood vessels, particularly arterioles, which increases blood flow. The regulation of blood vessel tone is primarily controlled by the autonomic nervous system, specifically the sympathetic and parasympathetic branches.
Sympathetic Nervous System:
The sympathetic nervous system typically causes vasoconstriction, which is the narrowing of blood vessels. It does this by releasing norepinephrine (noradrenaline) that binds to alpha-adrenergic receptors on smooth muscle cells of blood vessel walls, causing the muscle to contract. This increases vascular resistance and reduces blood flow to certain tissues.
When there is decreased activity of the sympathetic nervous system, there is less release of norepinephrine, leading to less activation of alpha-adrenergic receptors. This results in vasodilation, as the smooth muscle cells relax, and the vessels widen. This can improve blood flow and reduce blood pressure in certain areas of the body.
Parasympathetic Nervous System:
The parasympathetic nervous system generally has the opposite effect on the heart and blood vessels compared to the sympathetic nervous system. It mainly affects heart rate and digestive processes, but its role in directly controlling blood vessel tone is limited. However, in certain areas such as the skin, parasympathetic activity can indirectly cause vasodilation through the release of acetylcholine and other signaling molecules. Increased parasympathetic activity would cause vasodilation, but it is less directly involved in arteriole regulation than the sympathetic system.
In summary:
- Increased activity of the parasympathetic nervous system can cause vasodilation in some areas but is not the dominant factor in arterioles.
- Decreased sympathetic nervous activity leads to vasodilation in arterioles due to reduced vasoconstriction signals.
Thus, decreased activity of the sympathetic nervous system is the primary cause of vasodilation in arterioles.