The heart is a cardiac muscle composed of four chambers. The chambers are responsible for pumping blood throughout the body. The circulating blood delivers important nutrients and oxygen to tissues while bringing back toxins and wastes for filtering. The heart is fired by electrical impulses.
The four chambers of the heart are called atria and ventricles. The atria are located at the top, on the left and right sides of the heart. The ventricles are on the bottom left and right sides. The left side of the heart is responsible for circulating oxygenated blood into the body, while the right side takes deoxygenated blood and pumps it back into the lungs.
As you breathe, your lungs take in oxygen-rich air. This oxygen is absorbed by tissue in the lungs. The oxygen is then sent into the circulatory system. Blood comes from the lungs into the pulmonary vein which passes the blood to the left atrium. The left atrium pumps the blood into the left ventricle. The left ventricle then passes the blood through the aorta. The aorta will take the blood onwards throughout the body, supplying oxygen to all of your tissues.
When the blood comes back to the heart, is it depleted of oxygen. It also is carrying wastes and toxins. Because the blood must be purified and replenished, it passes back into the heart through either the superior or inferior venae cavae. The superior vena cava delivers blood from the head and upper body while the inferior vena cava delivers blood from the abdomen and lower extremities. The incoming blood enters the right atrium where it is pumped into the right ventricle. This ventricle then pushes the oxygen-deprived blood into the lungs.
Atria walls are thinner than those of the ventricles. Atria expand to receive incoming blood and ventricles contract and push. The atria work together and pump at the same time, which opens the valves leading into the ventricles. The ventricles contract at the about the same time, which causes the valves between the atria and ventricles to close.
There are also valves between the ventricles and the pulmonary artery and aorta which close with each contraction. This prevents any back flow of blood into the heart. The heart makes a distinct sound as it pumps, which is the closing and opening of the valves. If your valves are damaged, blood can leak backwards. This causes a swishing sound, or murmur.
Your heart beats due to electrical impulses. These impulses are generated in the sinoatrial node. All smooth muscle in your body contracts when a motor nerve stimulates it. In your heart’s case, it has the sinoatrial node to tell it when to contract and beat. This is like the action of a pacemaker, and is why a human heart will continue to beat even if taken out of the body. As long as the heart has an oxygen supply, it will contract and work.
The impulses sent by the sinoatrial node run along specialized cardiac muscle cells to the right and left atria. The atria contract and release simultaneously. These impulses are lightning quick and stimulate the next sequence of events. The second area of nodal tissue is the atrioventricular node. This node sends impulses along more specialized cardiac muscle cells which act in conjunction to stimulate the right and left ventricles. The ventricles contract almost at the same time. The delay is caused by the atrioventricular node, whose fibers are a bit slower to conduct impulses. This ends up working in your favor, however, as it ensures the atrial beat is finished before the ventricular beat begins.