How The Oxygen You Breathe Gets Delivered to the Cells of Your Body

The respiratory system is responsible for regulating oxygen and carbon dioxide levels in the blood. This process includes ventilation, gas exchange between air, blood, and tissues, and the use of oxygen for metabolism.

Inhalation draws oxygen into the body, through the nose and mouth, into the lungs, and finally into air sacs called alveoli. Here, gas exchange occurs, with oxygen entering the bloodstream and carbon dioxide exiting through small blood vessels called capillaries lining the alveoli.

Once in the capillaries, oxygen molecules dissolve into plasma and enter red blood cells (erythrocytes). These cells contain millions of hemoglobin proteins, each with four subunits capable of binding one oxygen molecule. The binding of one oxygen molecule to hemoglobin increases the affinity for subsequent oxygen molecules.

Dissolved and bound oxygen flows through the arterial bloodstream to capillaries in tissues. Upon arrival, carbon dioxide loading onto the erythrocyte promotes oxygen unloading. Cellular oxygen metabolism produces carbon dioxide gas as waste.

Carbon dioxide exits cells and tissues, converting into bicarbonate within the erythrocytes. This conversion releases hydrogen ions, which decrease hemoglobin's oxygen affinity, freeing oxygen for delivery to tissue cells. The carbon dioxide-rich blood then returns to the lungs via venous circulation and the pulmonary artery.

Inside each erythrocyte in the lungs, the bicarbonate conversion is reversed, recreating carbon dioxide. This carbon dioxide then diffuses across the erythrocyte into the alveoli and lungs, to be exhaled from the body.