The sequence of oxygen, carbon dioxide, and blood flow can be described as follows:
- Oxygen-poor (deoxygenated), carbon dioxide-rich blood returns to the heart’s right side through large veins (the superior and inferior vena cava).
- This blood is pumped from the right ventricle through the pulmonary artery to the lungs.
- In the lungs, blood flows through tiny capillaries surrounding the alveoli (air sacs). Here, oxygen from the inhaled air diffuses through the thin walls of the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli to be exhaled.
- The now oxygen-rich blood travels from the lungs through the pulmonary veins to the left side of the heart.
- The left ventricle pumps this oxygenated blood through the aorta and systemic arteries to the rest of the body.
- In the body’s tissues, oxygen diffuses from the blood into cells, and carbon dioxide produced by cellular metabolism diffuses into the blood.
- The blood, now carrying carbon dioxide and low oxygen, returns via veins to the right atrium of the heart, completing the cycle.
This continuous loop of pulmonary (heart to lungs and back) and systemic (heart to body and back) circulation ensures oxygen delivery to tissues and removal of carbon dioxide waste
