Why does the blood returning to the heart have very little oxygen in it
1 answer
The blood returning to the heart has very little oxygen in it because the oxygen in the blood was already used up by the body's tissues during circulation. In the systemic circulation, oxygen-rich blood is pumped from the heart to the body's tissues through arteries. The tissues extract the oxygen from the blood to fuel cellular respiration, and the oxygen-poor blood is returned to the heart through veins. This is called venous blood, and it contains carbon dioxide and other waste products from cellular metabolism. The heart then pumps the venous blood to the lungs, where it is oxygenated once again through the process of gas exchange.