The sequence of oxygen, carbon dioxide, and blood flow in the body involves a continuous cycle between the lungs, heart, and tissues:
- Oxygen enters the body through inhalation and reaches the lungs, specifically the alveoli, tiny air sacs surrounded by capillaries. Here, oxygen passes through a very thin barrier from the alveoli into the blood in the capillaries
- The oxygen-rich blood then travels from the lungs to the left side of the heart via the pulmonary veins. The heart pumps this oxygenated blood through the aorta and arteries to the rest of the body
- As blood flows through body tissues, oxygen is delivered to cells, and carbon dioxide, a waste product of cellular respiration, is absorbed into the blood. This deoxygenated, carbon dioxide-rich blood returns to the right side of the heart through veins
- From the right ventricle, the blood is pumped into the pulmonary arteries and sent back to the lungs. In the lungs, carbon dioxide diffuses from the blood into the alveoli to be exhaled, while oxygen is taken up again by the blood, completing the cycle
This process is supported by two interconnected circulatory loops: the systemic circulation, which delivers oxygenated blood to the body, and the pulmonary circulation, which exchanges gases in the lungs
. In summary, oxygen is inhaled and transferred to the blood in the lungs, pumped by the heart to the body, where it is used by cells; carbon dioxide produced by cells is carried back in the blood to the lungs to be exhaled, maintaining a vital exchange for life
