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How does the respiratory system bring oxygen into the body?

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Vintage anatomy chart showing front and back views of the human skeletal system and muscular system, with detailed illustrations of bones and muscles. — human body Vintage anatomy charts of the human body showing the skeletal and muscle systems.

The human respiratory system brings oxygen into the body through a coordinated process of ventilation and gas exchange.

Mechanics of Breathing

The process begins with ventilation, the movement of air between the environment and the lungs. This is driven by the diaphragm, the primary muscle of respiration. When the diaphragm contracts, it increases the volume of the thoracic cavity, lowering the internal pressure and drawing air into the lungs through the conducting airways—including the nose, pharynx, larynx, trachea, and bronchi.12

Gas Exchange

Once air reaches the pulmonary alveoli, oxygen enters the blood through diffusion. This process is driven by differences in partial pressure: oxygen moves from the alveoli, where its partial pressure is higher, across a thin membranous barrier into the pulmonary capillaries.34

Because oxygen is poorly soluble in blood, it is primarily transported to tissues by red blood cells via the circulatory system. The efficiency of this system is supported by the immense surface area of the alveoli and the continuous, well-matched flow of air and blood throughout the lungs.453