What happens to the blood when it reaches lungs?

When the blood reaches the lungs, it undergoes a crucial process called pulmonary circulation. Here's what happens to the blood in the lungs:

1. Blood Delivery: Deoxygenated blood from the body is carried to the lungs through the pulmonary arteries. Pulmonary arteries are blood vessels that carry blood from the heart to the lungs.

2. Gas Exchange: The lungs are filled with numerous tiny air sacs called alveoli, which provide a large surface area for efficient gas exchange. As the blood reaches the capillaries surrounding the alveoli, a process called external respiration occurs.

* Oxygen Absorption: Inside the capillaries, carbon dioxide (CO2), a waste product of cellular respiration, diffuses out of the blood into the alveoli. At the same time, oxygen (O2) from the inhaled air diffuses from the alveoli into the blood. This process oxygenates the blood.

* Hemoglobin: Hemoglobin, the oxygen-carrying protein in red blood cells, picks up oxygen molecules and becomes saturated with oxygen. Oxygenated blood carries approximately 98% of the total oxygen content, with most of it bound to hemoglobin.

3. Return to the Heart: Once the blood in the capillaries around the alveoli is oxygenated, it flows into small vessels called pulmonary venules. These venules merge to form pulmonary veins, which carry the freshly oxygenated blood back to the heart.

4. Complete Circuit: The oxygenated blood returns to the heart, specifically the left atrium, completing the pulmonary circulation. From the left atrium, it flows into the left ventricle, and during systole (contraction), it is pumped out of the heart via the aorta to provide oxygenated blood to all tissues and organs in the body, completing the systemic circulation.

In summary, the blood is oxygenated in the lungs, releasing carbon dioxide and absorbing oxygen in a process called gas exchange. The oxygenated blood is then carried by pulmonary veins back to the heart to be distributed to the entire body.