List the four chambers in an animal's heart.

A four-chamber heart is composed of two atria and two ventricles. The function of each chamber is briefly described below.

• Oxygen-poor blood that has been used by the cells is delivered back to the heat via the right atrium.


• The right atrium pumps this oxygen-depleted blood to the right ventricle.


• The right ventricle then pumps the blood to lungs, where oxygen is received.


• The oxygenated blood is brought back to the heart via the pulmonary veins.


• The pulmonary veins lead the blood to the left atrium.


• The left atrium pumps this oxygen-rich blood to the left ventricle.


• The left ventricle then pumps the oxygenated blood to the body.

The oxygen in the blood is then used by the mitochondria of the eukaryotic cells in a process known as cellular respiration. During cellular respiration, oxygen gas and the sugar glucose are converted into water, carbon dioxide gas, and an energy source called adenosine triphosphate (ATP).