Question

Explain four chambers of the mammalian heart in brief.

Answer 1

Hint: Warm bloodedness requires great deal of oxygen, as oxygen is used to generate both heat and ATP. Over a three-chambered heart, a four-chambered heart is an enormous evolutionary advantage.

Complete answer:
In mammals, the heart has four chambers: two atria and two ventricles. There is one atrium and one ventricle on the left and right side each. The ventricles are the chambers that pump blood; similarly the atria are the chambers that receive blood.
Right atrium: The atrium on the right side receives deoxygenated blood from the inferior vena cava which receives blood from the veins that come from the lower organs and the legs, and from the superior vena cava, which receives blood from the jugular vein that comes from the veins that come from the arms and from the brain. The right atrium also receives blood from the coronary sinus which drains the deoxygenated blood from the heart itself.
Right ventricle: This deoxygenated blood then passes to the right ventricle through tricuspid valve or the atrio-ventricular valve, a flap of connective tissue which opens in only one direction to prevent the backflow of blood. The valve separating the chambers on the left side of the heart valve is known as the mitral valve or the bicuspid valve. After it is filled, the right ventricle pumps blood through the pulmonary arteries, by-passing the pulmonic valve or the semilunar valve to the lungs for re-oxygenation. After the blood passes through the pulmonary arteries, right semilunar valves close to prevent the blood from flowing backwards into the right ventricle.
Left atrium: The left atrium then receives the oxygenated blood from the lungs via pulmonary veins.
Left ventricle: The blood from left atrium passes through the mitral valve or the atrioventricular valve on the left side of the heart or the bicuspid valve to the left ventricle, where the blood is pumped out through the aorta, which is the major artery of the body, taking oxygenated blood to the muscles and organs of the body. Once blood is pumped into the aorta and out of the left ventricle, the aortic valve or the aortic semilunar valve closes to prevent the blood from flowing backward into the left ventricle.

Note: The pumping pattern in mammals is referred to as double circulation. Chambered hearts with valves and relatively thick muscular walls are least common in invertebrates but it does occur in some mollusks, especially cephalopods (squid and octopus).