Question

When oxygen passes from the lungs into the circulatory system as a gas, how many cells does it have to pass through to be in the circulatory system?

Answer 1

Animal respiratory systems are intended to encourage gas exchange. In well evolved creatures, air is warmed and humidified in the nasal cavity. Air at that point goes down the pharynx, through the trachea, and into the lungs. In the lungs, air goes through the branching bronchi, achieving the respiratory bronchioles, which house the main site of gas exchange. The respiratory bronchioles open into the alveolar ducts, alveolar sacs, and alveoli. Since there are such huge numbers of alveoli and alveolar sacs in the lung, the surface area for gas trade is huge. A few defensive instruments are set up to forestall harm or contamination.