Is the blood enters the right atrium?

Answer 1

Blood entering the right atrium is blood returning from the upper and lower body and it has been to the cells and given up all its oxygen. This is sometimes called blue blood and is very dark in colour. [A high oxygen content would cause it to be bright red]. In place of oxygen, it is now carrying carbon dioxide and this blood will enter the right side of the heart where it will be pumped a short distance to the lungs. The carbon dioxide will be exchanged for oxygen and this red blood is then pumped back to the heart, only this time it arrives at the left side, the left atrium, then into the left ventricle where it is pumped all around the body. Hope this helps.