Question

What does increasing sympathetic tone do to the respiratory system?

		B. It increase pulmonary perfusion by increasing cardiac output.
		A. It increases blood pressure by contracting arterial smooth muscles, thus increasing pulmonary blood flow.
		C. It decreases pulmonary ventilation by bronchoconstriction.
		D. It increases pulmonary ventilation by bronchodilation.

Answer 1

The sympathetic tone controls the physiological systems of our body by neurotransmitters like adrenaline, noradrenaline, and dopamine. The actions of these neurotransmitters are mediated through adrenergic receptors like Alpha and Beta-adrenergic receptors.

In the respiratory system, the bronchial smooth muscles possess Beta2 receptors upon sympathetic stimulation receptors to cause bronchodilation and inhibition of release of allergic mediators from mast cells present in the lungs. The blood vessels of the mucus membrane and upper respiratory tract possess Alpha1 receptors they cause vasoconstriction upon sympathetic stimulation.

These effects of Beta2 and Alpha1 receptors lead to a reduction in bronchial resistance and connection. Both of these effects help to increase pulmonary ventilation.

Hence, the correct answer is D. It increases pulmonary ventilation by bronchodilation.