The heart and circulation — Edexcel International GCSE Science (Double Award)
Heart structure and function, heart rate and adrenaline, coronary heart disease, blood vessels and the circulation of blood around the body.
Revision notes
5 short notes, in the order of the specification. Each one in short:
The heart is a muscular pump with four chambers: two atria that receive blood and two ventricles that pump it out. The septum separates the left and right sides so oxygenated and deoxygenated blood do not mix, and valves prevent backflow. The left ventricle has the thickest wall because it pumps blood around the whole body.
Heart rate is the number of heartbeats per minute. During exercise the muscles respire faster, so they need more oxygen and glucose and produce more carbon dioxide. The heart rate increases so blood delivers these faster and removes carbon dioxide. Adrenaline, released by the adrenal glands when frightened or excited, also increases heart rate.
Coronary heart disease is a disease in which layers of fatty material build up inside the coronary arteries and narrow them. Less blood reaches the heart muscle, so it gets less oxygen, which can cause chest pain and a heart attack. Risk factors include a diet high in saturated fat and cholesterol, smoking, high blood pressure and lack of exercise.
Arteries, veins and capillaries are the three types of blood vessel. Arteries carry blood away from the heart at high pressure, so they have thick, muscular walls with elastic fibres. Veins carry blood back to the heart at low pressure, with a wide lumen and valves to stop backflow. Capillaries have walls one cell thick for exchanging substances with cells.
Humans have a double circulatory system: blood passes through the heart twice on each complete circuit, once to the lungs and back and once to the rest of the body and back. Blood leaves the heart in the aorta and pulmonary artery. The hepatic portal vein carries blood rich in digested food from the gut to the liver.
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Quick check questions
What is the function of the septum?
Show answer
It separates the left and right sides of the heart, so oxygenated and deoxygenated blood do not mix.
Why is the wall of the left ventricle thicker than the right?
Show answer
It pumps blood around the whole body, which needs higher pressure.
Why does heart rate rise during exercise?
Show answer
Muscles respire faster, so more oxygen and glucose must be delivered and more carbon dioxide removed.
Name the blood vessels that supply the heart muscle.
Show answer
Coronary arteries.
Which vessel carries blood from the gut to the liver?
Show answer
The hepatic portal vein.
Frequently asked questions
Why is the left ventricle thicker than the right?
The left ventricle has a thicker, more muscular wall than the right because it pumps blood all the way around the body through the aorta, which needs a higher pressure. The right ventricle pumps deoxygenated blood only to the nearby lungs through the pulmonary artery, so it needs less pressure and a thinner wall.
How does the heart pump blood?
The heart pumps blood by contracting its muscular chambers. Deoxygenated blood enters the right atrium from the vena cava, passes to the right ventricle and is pumped to the lungs. Oxygenated blood returns to the left atrium in the pulmonary vein, passes to the left ventricle and is pumped to the body through the aorta. Valves prevent backflow.
Why do arteries have thick elastic walls?
Arteries have thick, muscular walls with elastic fibres because they carry blood away from the heart at high pressure. The thick wall can withstand the high pressure, and the elastic fibres let it stretch and spring back with each heartbeat. Arteries have a narrow lumen and no valves.
Why do veins have valves but arteries do not?
Veins have valves because they carry blood back to the heart at low pressure, and the valves stop it flowing backwards. Arteries carry blood at high pressure straight from the heart, so they do not need valves. Veins also have a wide lumen and a thinner wall, which lets blood flow easily.
What causes coronary heart disease?
Coronary heart disease is caused by layers of fatty material building up inside the coronary arteries, which supply the heart muscle. The narrowed arteries let less blood through, so the heart muscle gets less oxygen, which can cause chest pain or a heart attack. Smoking, high blood pressure and a diet high in saturated fat increase the risk.
Written and checked against the Edexcel IGCSE Science Double Award (4SD0) specification · Updated October 2026