The function of the heart, in relation to circulation, is to pump the blood around the blood vessels in order to deliver properties such as nutrients, oxygen and some hormones to the various cells. Waste materials also travel within the circulatory system and are ultimately eliminated from the body. The heart also circulates the blood to the lungs to restore the blood oxygen levels; the blood then comes back to the heart oxygenated.
The heart is situated in the cavity between the lungs and this is known as the thoracic cavity within the mediastium. It lies slightly to the left and is roughly the same size as the fist.
The heart's interior is made up of four separate chambers, the two upper chambers are referred to as the atria, and these are situated above the two chambers named the ventricles. A wall known as the septum divides the heart with one atrium and one ventricle on each side.
The four valves within the heart control one way blood flow in and out of the chambers. The tricuspid valve also referred to as the right atrioventricular, and the pulmonary valve are located on the right side of the heart. The mitral valve, also known as the left atrioventricular, and the aortic valve are situated on the left.
The heart pumps oxygenated blood out to the blood vessels within the body through the aorta, the blood transported to the head, neck and the arms leaves the heart from the aortic arch. Blood travelling to the lower body flows out of the heart from the descending aorta. Nutrients, oxygen and a variety of hormones are delivered throughout the body and then the blood returns to the heart deoxygenated.
The blood returning from the upper body enters the heart through a large vein known as the superior vena cava, and blood from the rest of the body comes back into the heart via the inferior vena cava. From here the blood enters into the right atrium which contracts and this is known as atrial systole. Following atrial systole the tricuspid (right atrioventricular) valve opens, the blood then flows through into the right ventricle which contracts and this is referred to as ventriclar systole, this pushes the blood into the pulmonary valve and then out into the pulmonary artery. The blood is then transported to the lungs where the gaseous exchange takes place and then the blood returns to the heart with a fresh supply of oxygen.
The oxygenated blood returns from the lungs and enters the heart from the pulmonary veins at the left atrium, atrial systole occurs and pushes the blood through the mitral (left atrioventricular) valve into the left ventricle, and then ventricular systole takes place and propels the blood through the aortic valve and out into the aorta.
Blood circulation between the heart and lungs is referred to as pulmonary circulation. That which involves the heart and the rest of the body is known as systemic circulation. The right side of the heart manages the circulation of deoxygenated blood, and the left side is responsible for the circulation of oxygenated blood, however, they both work in conjunction to each other, as deoxygenated blood enters into the right atrium at the same time as oxygenated blood comes into the left atrium, and the blood leaves both ventricles simultaneously.