Question: why do we need to study respiratory system

title: Respiratory system
text: There are oxygen sensors in the smaller bronchi and bronchioles . In response to low partial pressures of oxygen in the inhaled air these sensors reflexly cause the pulmonary arterioles to constrict . ( This is the exact opposite of the corresponding reflex in the tissues , where low arterial partial pressures of O cause arteriolar vasodilation . ) At altitude this causes the pulmonary arterial pressure to rise resulting in a much more even distribution of blood flow to the lungs than occurs at sea level . At sea level the pulmonary arterial pressure is very low , with the result that the tops of the lungs receive far less blood than the bases , which are relatively over-perfused with blood . It is only in middle of the lungs that the blood and air flow to the alveoli are ideally matched . At altitude this variation in the ventilation / perfusion ratio of alveoli from the tops of the lungs to the bottoms is eliminated , with all the alveoli perfused and ventilated in more or less the physiologically ideal manner . This is a further important contributor to the acclimatatization to high altitudes and low oxygen pressures .