ANATOMY

Detailed explanation-1: -Oxygen is inhaled into the lungs and passes through the alveoli (the tiny air sacs at the end of the bronchioles ) and into the bloodstream (see inset), where it travels to the tissues throughout the body.

Detailed explanation-2: -In a process called diffusion, oxygen moves from the alveoli to the blood through the capillaries (tiny blood vessels) lining the alveolar walls. Once in the bloodstream, oxygen gets picked up by the hemoglobin in red blood cells.

Detailed explanation-3: -Gas exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them. As shown below, inhaled oxygen moves from the alveoli to the blood in the capillaries, and carbon dioxide moves from the blood in the capillaries to the air in the alveoli.