Heart is the main organ of the body. It’s size is according to one’s fist size. It provides blood to the body by moving it around.
To start with, the heart is roughly conical in shape. It has four chambers. The upper two are called atria (singular; atrium). The lower chambers are called ventricles. The heart has two thick membranes called the pericardium. These two membranes have pericardial fluid in between them to prevent friction while the heart beats.
Blood comes into the heart from the vena cavas. The blood from the head, neck and the arms come from the superior vena cava while blood from the rest of the body enters the heart from the inferior vena cava which is found below the superior vena cava. The pulmonary arteries also leave the heart through pulmonary arch or trunk which is connected to the right ventricle. The pulmonary arteries are divided into two extended tubes which reach each lung. The purpose for which it takes blood there is that it does not have any oxygen. After gaseous exchange occurs the blood is sent back to the heart by the pulmonary veins which open to the left atrium.
The tricusped valve is located between the right atrium and the right ventricle and has 3 flaps while the bicuspad valve is located between the left atrium and the left ventricle and has only 2 flaps.
The chordea tendanea prevents the valves from opening while the blood is in the ventricles.
When the blood returns to the heart through the inferior and superior vena cava there is no oxygen in it. The right atrium is filled with blood. The tricuspad valve opens up and the blood flows to the right ventricle. The tricuspad valve then closes and the blood remains in the ventricle. Then the heart contracts and the blood is pushed to the pulmonary arch through the semi lunar valve. This valve also closes to prevent back flow.
Receiving oxygen the blood flows through the pulmonary veins and enter the left atrium. The same thing happens and the blood is pushed to the aortic arch which then spreads the blood across the body. To push the blood the heart contracts (systole action) and relaxes (diastole action) per second. This makes up a heartbeat.
The walls of the heart that are too thick prevent the heart from bursting or being damaged while contracting and relaxing.