The diagram below shows the internal structure of the heart. The yellow arrows show the direction of blood flow through the heart.
The Chambers
The heart consists of four chambers; two atria that receive blood and two ventricles that pump blood out of the heart.
Right Atrium – receives deoxygenated blood from the superior and inferior vena cavae which it then pumps to the right ventricle.
Right Ventricle – receives deoxygenated blood from the right atrium and pumps it towards the lungs through the pulmonary artery were it can be oxygenated. The walls of the ventricles are thicker than the atria because they have to pump blood out of the heart. Whereas, the atria only have to pump blood to the ventricles.
Left Atrium – receives oxygenated blood from the pulmonary veins which it then pumps to the left ventricle.
Left Ventricle – receives oxygenated blood from the left atrium and pumps it around the body. The walls of the left ventricle are thicker and more muscular than the walls of the right ventricle. This allows them to contract more powerfully as more pressure is required to pump the blood around the rest of the body than just to the lungs.
The Blood Vessels
Below is a list of the main blood vessels that carry blood to and away from the heart.
Superior Vena Cava – a vein that carries deoxygenated blood from the upper half of the body to the heart.
Inferior Vena Cava – a vein that carries deoxygenated blood from the lower half of the body to the heart.
Pulmonary Artery – an artery that carries deoxygenated blood from the heart to the lungs.
Pulmonary Veins – veins that carries oxygenated blood from the lungs to the heart.
Aorta – the largest artery in the body that carries oxygenated blood from the heart to the rest of the body.
The Valves
The heart has four valves that separate the atria from the ventricle and the ventricles from the arteries. The valves open and close as the heart beats allowing blood to flow in one direction only and preventing back-flow.
The valves open when the pressure behind them is greater than in front and are forced shut when the pressure in front of them is greater than behind them.
Tricuspid Valve – separates the right atrium from the right ventricle, preventing blood from flowing back into the atrium when the ventricles contract. It is also sometimes called the right atrioventricular valve.
Right Semilunar Valve – separates the right ventricle from the pulmonary artery, preventing blood from flowing back into the ventricle when they contract. It is also sometimes called the pulmonary valve.
Bicuspid Valve – separates the left atrium from the left ventricle, preventing blood from flowing back into the atrium when the ventricles contract. It is also sometimes called the left atrioventricular valve or the mitral valve.
Left Semilunar Valve – separates the left ventricle from the aorta, preventing blood from flowing back into the ventricle when they contract. It is also sometimes called the aortic valve.
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