Physiology of breathing I

The main function of the respiratory system is gas exchange. The lungs also break down microthrombi arriving from the veins, and have several metabolic actions, including the activation of angiotensin I to angiotensin II and the breakdown or deactivation of substances (e.g. 5-hydroxytryptamine, bradykinin, noradrenaline, acetylcholine, some drugs). This contribution discusses lung volumes and ventilation, respiratory muscles and the mechanism of breathing, and resistance to breathing.