Complete the passage to describe the function of the heart.
The pumping of the heart involves the alternate contraction and relaxation of the chambers of the heart. The upper chambers of the heart are called
, and the lower chambers of the heart are called
.
The upper chambers of the heart are called atria, and the lower chambers of the heart are called ventricles. The atria receive blood from the veins and then squeeze it into the ventricles. The ventricles pump the blood out of the heart through the arteries to the rest of the body. This continuous process ensures that oxygen-rich blood is circulated throughout the body and carbon dioxide is removed, providing essential nutrients and oxygen to the body's tissues and organs.
