How and where is the blood enriched with oxygen in humans?

The lungs enrich the blood with oxygen.

The process of circulating oxygen-rich blood in humans is as follows:-

1. A human heart has four chambers :

(i) Right atrium (ii) Left atrium (iii) Right ventricle (iv) Left ventricle.

2. The oxygen-deficient blood enters the Right Atrium from the whole body and then flows into Right Ventricle.

3. From there, this oxygen-deficient blood is transported to the lungs.

4. Here, in the lungs, the blood gets enriched with oxygen.

5. From here, the oxygen-rich blood enters the Left Atrium of the heart, from the lungs, via four pulmonary veins.

6. Now, the blood enters the Left ventricle from the Left Atrium, which pumps the oxygen-rich blood to the whole body through the aorta and the arterial system.