IGCSE Biology / Blood and circulation

The structure of the heart revision notes

Edexcel International GCSE Biology (4BI1), chapter 5: Blood and circulation, specification point 2.65. Free lesson.

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The heart has four chambers, valves and main vessels arranged to keep blood flowing in the right direction. Its structure keeps oxygenated and deoxygenated blood separate and allows blood to be pumped to the lungs and the rest of the body.

What the main vessels connect to

The vena cava brings deoxygenated blood back from the body to the right side of the heart. Blood travels from the right side to the lungs, then returns to the left side and is pumped around the body. Pulmonary artery: carries blood from the right ventricle to the lungs. Pulmonary vein: brings blood from the lungs to the left atrium. Aorta: carries blood from the left ventricle to the body. It has the thickest wall of the vessels. Coronary arteries: branch from the aorta and supply the heart muscle itself. The heart muscle cannot get the oxygen it needs from blood inside…

What the chambers and septum do

The two upper chambers are the atria. They receive blood and push it into the ventricles below. The lower chambers, called ventricles, pump blood out of the heart. The right atrium receives blood from the vena cava. Its thin wall only pushes blood into the right ventricle. The right ventricle pumps blood to the nearby lungs. Its wall is thicker than an atrium's, but thinner than the left ventricle's. The left atrium receives blood from the pulmonary vein. The left ventricle pumps blood to the whole body, so its wall is much thicker. It must generate enough pressure to overcome greater…

How the valves prevent backflow

Valves keep blood moving forwards. They open to let blood pass and close to stop it flowing backwards. Atrioventricular (AV) valves sit between each atrium and ventricle. They stop blood flowing back into the atria. Semilunar valves sit at the base of the pulmonary artery and the aorta. They stop blood flowing back into the ventricles.

How blood moves through the heart

Blood passes through the chambers in a set order. The heart's two sides contract at the same time, keeping the circuits to the lungs and body in step.

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