J Receptor Reflexes Terminate Exercise to Reduce Pulmonary Inflow

Abstract

A great increase in ventilation and cardiac output is set off by and even before rapid locomotion begins. An investigation into the neural mechanisms involved revealed that the subsequent increase in pulmonary blood flow stimulates J or juxtapulmonary capillary receptors that lie in the pulmonary parenchyma. Reflexes arising from stimulation of these sensory receptors are an increase in ventilation accompanied by sensations of breathlessness, bradycardia and reduction or stopping of exercise. Of these, the significance of reflex bradycardia is to reduce the great rise in pulmonary capillary pressure during strenuous exercise and protect the pulmonary arterioles from rupture as they are vulnerable to mechanical stress.