The pathway of oxygen in the breathing system can be described as follows:
- Oxygen enters the body through inhalation via the nose or mouth, where the air is warmed, moistened, and filtered
- The air then travels down the pharynx (throat) and passes through the larynx (voice box) into the trachea (windpipe)
- From the trachea, air moves into the two primary bronchi, each leading into a lung. These bronchi branch repeatedly into smaller tubes called secondary and tertiary bronchi, and then into even smaller bronchioles
- The bronchioles end in clusters of tiny air sacs called alveoli, which are surrounded by a network of capillaries (tiny blood vessels)
- Oxygen diffuses across the thin walls of the alveoli and the capillaries into the blood. This diffusion occurs because the oxygen concentration is higher in the alveoli than in the blood
- Once in the blood, oxygen binds to hemoglobin molecules in red blood cells and is transported via the pulmonary veins to the left side of the heart
- The heart pumps the oxygen-rich blood through arteries to tissues and cells throughout the body, where oxygen is released for cellular respiration, producing energy
- Carbon dioxide, a waste product of cellular respiration, diffuses from the cells into the blood, is transported back to the lungs, and is expelled during exhalation
This entire process involves ventilation (air movement in and out of lungs), diffusion (gas exchange at alveoli), and perfusion (blood flow through lungs)
. In summary, oxygen travels from the external environment through the nose/mouth → pharynx → larynx → trachea → bronchi → bronchioles → alveoli → diffuses into blood → transported by heart to body tissues
