From where does oxygen diffuse after entering the alveoli?

Oxygen diffusion in the lungs primarily occurs from the alveoli into the capillaries, which is why the correct answer is capillaries. When air is inhaled, it travels through the respiratory system and reaches the alveoli, tiny air sacs in the lungs where gas exchange takes place. The walls of the alveoli are extremely thin, allowing for the efficient transfer of oxygen from the air within the alveoli into the bloodstream.

Once in the capillaries, oxygen binds to hemoglobin in red blood cells and gets transported throughout the body to supply oxygen to tissues and organs. This process is crucial for sustaining cellular metabolism and overall body function. The reverse also occurs, with carbon dioxide diffusing from the blood into the alveoli, where it can be exhaled.

In contrast, structures such as the bronchi, trachea, and pharynx are parts of the respiratory pathway but do not participate directly in the oxygen exchange process. They serve primarily as conduits for air movement rather than sites for diffusion.