Structure of the cardiovascular system
If you clench your hand into a fist, this is approximately the same size as your heart. It is located in the middle of the chest and slightly towards the left.
The heart is a large muscular pump and is divided into two halves - the right-hand side and the left-hand side.
The right-hand side of the heart is responsible for pumping deoxygenated blood to the lungs.
The left-hand side pumps oxygenated blood around the body.
Each side of the heart consists of an atrium and a ventricle which are two connected chambers.
The atria (plural of atrium) are where the blood collects when it enters the heart.
The ventricles pump the blood out of the heart to the lungs or around the body.
The septum separates the right-hand and left-hand side of the heart.
The tricuspid valve separates the right atrium and right ventricle. It opens due to a build-up of pressure in the right atrium, and prevents back flow of blood from the right ventricle to the right atrium.
The bicuspid valve separates the left atrium and left ventricle and prevents back flow of blood from the ventricle to the atrium. It likewise opens due to a build-up of pressure, this time in the left atrium.
The semilunar valves stop the back flow of blood into the heart. There is a semilunar valve where the aorta leaves the left ventricle and another where the pulmonary artery leaves the right ventricle.
Blood vessels leading into and out of the heart
There are four main blood vessels that take blood into and out of the heart.
The aorta is the largest artery in the body. It carries oxygenated blood away from the left ventricle to the body.
The vena cava is the largest vein in the body. It carries deoxygenated blood from the body back to the heart.
The pulmonary artery carries deoxygenated blood away from the right ventricle to the lungs.
The pulmonary vein returns oxygenated blood from the lungs to the heart.
Arteries carry oxygenated blood away from the heart (except for the pulmonary artery which carries deoxygenated blood away from the right ventricle to the lungs).
The main artery is the aorta.
The main vein is the vena cava.
The double-circulatory system
The heart works as a dual action pump – two pumps that work at the same time to pump blood in two different directions.
The right-hand side of the heart collects deoxygenated blood from the body and pumps it to the lungs (to collect more oxygen). This is called pulmonary circulation.
The left-hand side of the heart collects oxygenated blood from the heart and pumps it round the body. This is called systemic circulation.
The pathway of blood through the heart
Left-hand side
Oxygenated blood is carried to the heart from the lungs in the pulmonary vein. It goes into the left atrium, through the bicuspid valve and into the left ventricle. The ventricle pumps the blood through the semilunar valve, into the aorta and round the body.
Right-hand side
Deoxygenated blood from the body is carried to the heart in the vena cava. It goes into the right atrium, through the tricuspid valve and into the right ventricle. The ventricle pumps the blood through the semilunar valve, into the pulmonary artery and to the lungs.