HCL Learning | Structure of the Human Heart

The human heart has four chambers. The two upper chambers are the atria and the two lower chambers are the ventricles. The interatrial septum separates the two atria and the interventricular septum is the partition between the two ventricles. The right atrium and right ventricle are connected through a tricuspid valve. As the name suggests, it has three leaflets or cusps. On the other side, the left atrium and ventricle are connected through a bicuspid valve. The bicuspid valve is also called the mitral valve because of its resemblance to a bishop's two-sided mitre or hat. The leaflets of these atrioventricular valves are connected to fibrous tissue called the chordae tendineae which in turn are attached to papillary muscles. Contraction and relaxation of these muscles make the valves open and close. There are also valves at the opening of the pulmonary trunk and the aorta. These are called the pulmonary valve and the aortic valve, respectively. Because of their crescent moon shape, these two valves are also called semilunar valves. The characteristic double-up sound of the heartbeat is produced during the closing of the heart valves. The thickness of the walls of the four heart chambers varies with their functions. The walls of the atria are thinner than those of the ventricles as the blood needs to be pumped into adjacent ventricles only. The left ventricle pumps blood a greater distance at higher pressure. Therefore, the wall of the left ventricle is thicker than that of the right ventricle. The sinoatrial node, atrioventricular node, bundle of HIS and Purkinje fibers represent the specialized cardiac tissue. These fibers are auto-excitable as they have the potential to generate electrical activity without any external stimuli. This makes the heartbeat continuously.