Summary
Highlights
Air reaches the alveoli deep within the lungs, where oxygen leaves the air to enter the blood, and carbon dioxide escapes from the blood to be expelled back into the air. This gas exchange happens at the level of the capillaries lining the alveolar walls.
With 600 to 800 million alveoli, the total contact surface between air and blood in the lungs is about 100 m², equivalent to a tennis court. This large, richly vascularized surface increases the amount of oxygen entering the blood.
Blood, enriched with oxygen after passing through the alveoli, leaves the lungs via the pulmonary vein to irrigate the body's various organs. It returns to the heart, which pumps it through the circulatory system, distributing oxygen to all organs.
At the cellular level of the organs, the reverse exchange occurs: blood delivers oxygen for cellular metabolism, which produces CO2 as waste. This CO2 is then collected by the blood and transported back to the pulmonary alveoli.
In essence, the respiratory system's role is to capture atmospheric oxygen and deliver it to the blood, while simultaneously extracting CO2 from the blood to expel it into the atmosphere.
During inhalation, air enters through the nose, passes through the nasal passages, pharynx, larynx, trachea, and bronchi, dividing into smaller bronchioles that lead to the alveoli. These fragile, grape-shaped sacs are where gas exchange occurs.
The main function of the respiratory system is to supply the body with oxygen and, at the same time, rid it of carbon dioxide.