Ventricles Contract

The heart is crucial to all walks of life and although the heart is approximately the size of a fist, it plays a vital role in life. The heart is broken down into four chambers, four valves, and different arteries and veins along with it. The atrium are located on the upper half of the heart, known as the right and left atria. On the bottom half of the heart, the chambers are known as the right and left ventricles. The atria work together simultaneously and then the ventricles will work in a synchronized manner. The atria will contract and then the ventricles will in tandem. Although it seems simple enough, the heart is one extraordinary organ that has a mind of its own.

It all starts with the sinoatrial (SA) node in the upper right corner

of the right atrium. The SA node, also known as the pacemaker of the heart, starts off the heartbeat and allowing for a rhythm to follow. The depolarization rate, negative to positive, is so high that it tells the atria to contract. As soon as the signal leaves the SA node it arrives at the atrioventricular (AV) node, and there is a pause allowing the rest of the blood to exit the atria into the ventricles. The blood passes through the atrioventricular valves. On the right side of the heart, blood passes through the right AV valve, also known as the tricuspid valve. On the left side of the heart blood is passed from the left atrium to the left ventricle via the mitral valve, also known as the left AV valve or the bicuspid.
As the blood now flows into the lower chambers of the heart, the impulse from the AV node now jumps to the AV bundle, also known as the bundle of His.

From there the impulse travels along the left and right bundle branches in the septum of the heart all the way to the Purkinje fibers. At this point, the blood has flowed from the atria to the ventricles. The impulse signal in the Purkinje fibers is allowing the apex of the heart to contract. Allowing the apex to contract first allows for the heart to work more efficiently. As soon as the apex contracts, the AV valves close and the walls of the heart begin to contract which pull the papillary muscles. The papillary muscles have chordae tendineae that attach themselves to the atrioventricular valves. These chordae tendineae work to try and prevent AV valve prolapse. When the pressure is great enough in the ventricles to overcome the resting blood on the other side of the arteries, the blood will be pushed out of the ventricles and will be passed through the semilunar valves. The right ventricle pushed blood through the pulmonary semilunar valve, and the left ventricle will push blood through the aortic semilunar valve. When the ventricles have expelled as much blood as they can and the pressure returns to a lower level the heart will begin to relax allowing the semilunar valves to close. Excess blood that does not get pushed along the arteries will remain on the artery side of the semilunar

valves.
The blood that passed through the pulmonary semilunar valve travels along the pulmonary arteries to the lungs where they get passed down from arteries, to arterioles, to the capillary beds where the gas exchange occurs from carbon dioxide to oxygen occurs. From there, the blood is now oxygenated travels to the venules, and veins and reaches the pulmonary veins arriving into the left atrium. The blood that had passed through the aortic semilunar valve travels through the aorta to the rest of the body. The left side of the heart is known as the systemic circuit because of its job to supply oxygenated blood to the body. After the blood travels to the parts of the body it needs to come back to the heart once again. As the blood travels from arteries, arterioles, capillaries, venules, back to the veins once again the blood finds itself back passing through the vena cavas to the right atrium again to repeat the cycle.
One of the most ingenious aspects of the heart is how it supplies itself with blood. As the heart is pumping and working it is not supplying blood to itself. Only when the heart is relaxed does it get blood. As the aortic semilunar valve slams open, the leaflet of the valve covers the opening in the aorta of the coronary arteries. So as the heart contracts, the artery opening is blocked. As the heart relaxes and the valve closes the artery opening is now uncovered and the backflow of blood can now pass through the coronary arteries. The blood passes along the coronary arteries and into arterioles, the capillary beds and back through the venules, and veins to return to the coronary sinus. The blood pools into the sinus and then flows back into the right atrium. The heart then starts all over again for another heart beat