Why does sympathetic activity constrict pulmonary vessels?

Question

I don't know understand why sympathetic stimulation constricts pulmonary vessels? I thought that the sympathetic nervous system activated the body for physical activity. Physical activity would need more oxygen supply. Doesn't constriction of pulmonary vessels reduce the gas exchange?

Answer 1

Sympathetic activity can cause both bronchodilation and vasoconstriction in the respiratory system, but the effects are mediated by different receptors and have different purposes.

Bronchodilation is primarily mediated by beta-adrenergic receptors on the smooth muscle cells that line the airways. When these receptors are activated by sympathetic activity, they cause the smooth muscle to relax, leading to dilation or widening of the airways. This helps to increase the flow of air into and out of the lungs, which can improve oxygen delivery to the tissues.

On the other hand, vasoconstriction in the pulmonary vessels is primarily mediated by alpha-adrenergic receptors on the smooth muscle cells that line the blood vessels. When these receptors are activated by sympathetic activity, they cause the smooth muscle to contract, leading to narrowing or constriction of the blood vessels. This can increase resistance to blood flow and decrease blood flow to the lungs.

The reason for this differential response is that the airways and the pulmonary blood vessels have different functions and different needs. Bronchodilation helps to increase airflow to the lungs and improve oxygen delivery to the tissues, while vasoconstriction helps to redirect blood flow away from the lungs and towards other organs during periods of stress or exercise.

In summary, sympathetic activity can cause both bronchodilation and vasoconstriction in the respiratory system, but the effects are mediated by different receptors and have different purposes. Bronchodilation helps to increase airflow and oxygen delivery to the tissues, while vasoconstriction helps to redirect blood flow away from the lungs and towards other organs during periods of stress or exercise.

Answer 2

Adrenergic or sympathetic stimulation vasoconstriction all vessels, pulmonary or otherwise, in order to increase the cardiac output of the heart. Gas exchange is increased in adrenergic stimulation through bronchodilation.