From which part of the heart does blood enter the right atrium?

Blood enters the right atrium primarily from the vena cava, which consists of two major veins: the superior vena cava and the inferior vena cava. The superior vena cava brings deoxygenated blood from the upper parts of the body, such as the head, neck, and arms, while the inferior vena cava carries deoxygenated blood from the lower parts of the body, including the abdomen and legs. Once the blood is collected in the right atrium, it is then directed into the right ventricle, from where it will move to the lungs for oxygenation. Understanding the role of the vena cava is essential in grasping how the circulatory system functions, particularly in managing deoxygenated blood returning to the heart.