(1) The heart is an organ that beats continuously to act as a pump for the transport of blood, which carries other substances with it.
(2) The human heart is divided into four chambers. The upper two chambers are called the right and left atrium and the lower two chambers are called the right and left ventricles.
(3) The partition between the chambers helps to avoid mixing up blood-rich oxygen with the blood-rich in carbon dioxide.
(4) The right atrium receives carbon dioxide-rich blood from the body. Blood from the right atrium enters the right ventricle, which contracts and pumps the blood to the lungs.
(5) On the other hand, oxygen-rich blood from the lungs returns to the left atrium. From the left atrium, blood enters the left ventricle. Left ventricle contracts and pumps the blood to all parts of the body.
(6) Hence, the rhythmic contraction and expansion of various chambers of the heart maintain the transport of oxygen to all parts of the body.
Blood flows from the heart to the lungs and back to the heart from where it is pumped to the rest of the body.