How does the heart pump blood around the body, and how are arteries, veins and capillaries suited to their jobs?
The structure and function of the heart, the double circulation, the pathway of blood through the heart and major vessels, and the structure and function of arteries, veins and capillaries.
A focused answer to the WJEC GCSE Biology section 1.4 topic on the heart and blood vessels, covering the structure and function of the heart, the double circulation and pathway of blood, the role of valves, and the structure and function of arteries, veins and capillaries.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
WJEC wants you to describe the structure of the heart and the double circulation, trace the pathway of blood through the heart and major vessels, explain the role of valves, and compare the structure and function of arteries, veins and capillaries.
The structure of the heart
The heart is a muscular organ divided into four chambers: two upper atria and two lower ventricles, separated into left and right sides by a wall called the septum.
- The right atrium receives deoxygenated blood from the body; the right ventricle pumps it to the lungs.
- The left atrium receives oxygenated blood from the lungs; the left ventricle pumps it to the body.
The left ventricle wall is thicker and more muscular than the right, because it must create a higher pressure to pump blood all the way around the body, while the right ventricle only pumps to the nearby lungs.
Double circulation
Humans have a double circulation: blood passes through the heart twice for each complete circuit of the body.
The pathway of blood is:
- Deoxygenated blood returns from the body in the vena cava to the right atrium.
- It passes into the right ventricle, which pumps it through the pulmonary artery to the lungs.
- In the lungs the blood picks up oxygen and returns in the pulmonary vein to the left atrium.
- It passes into the left ventricle, which pumps it through the aorta to the whole body.
The coronary arteries branch from the aorta to supply the heart muscle itself with oxygen and glucose.
The role of valves
The heart contains valves that make sure blood flows only one way. When the heart muscle relaxes, the valves stop blood flowing backwards, so each pump pushes blood forward through the circulation. Veins also contain valves, for the same reason.
Arteries, veins and capillaries
The three types of blood vessel are each suited to their function.
| Vessel | Wall | Lumen | Carries blood | Special feature |
|---|---|---|---|---|
| Artery | Thick, muscular, elastic | Small | Away from heart, high pressure | Withstands pressure |
| Vein | Thinner | Large | To heart, low pressure | Valves prevent backflow |
| Capillary | One cell thick | Very narrow | Through tissues | Site of exchange |
- Arteries carry blood away from the heart at high pressure, so they have thick, muscular and elastic walls and a small lumen to withstand and maintain the pressure.
- Veins carry blood back to the heart at low pressure, so they have thinner walls and a larger lumen, with valves to stop the blood flowing backwards.
- Capillaries are where substances are exchanged with the tissues. Their walls are only one cell thick, giving a short diffusion distance so oxygen and glucose can pass to the cells and waste can pass into the blood.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style4 marksExplain why the wall of the left ventricle is thicker and more muscular than the wall of the right ventricle.Show worked answer →
A 4-mark explanation linking structure to function.
The right ventricle pumps blood only to the lungs, which are close by and need a lower pressure. The left ventricle pumps blood to the whole body, which is much further, so it must produce a higher pressure. A thicker, more muscular wall can contract more strongly to create this higher pressure, pushing blood all the way around the body.
Markers reward: left ventricle pumps to the whole body; needs higher pressure; thicker muscle contracts harder; right pumps only to the nearby lungs at lower pressure. Saying the left side "has more blood" is not the reason.
WJEC style4 marksCompare the structure of an artery and a vein, and explain how each is suited to its function.Show worked answer →
A 4-mark compare question.
An artery has a thick, muscular and elastic wall and a small lumen, suited to carrying blood away from the heart at high pressure; the strong wall withstands and smooths the pressure. A vein has a thinner wall and a larger lumen, carrying blood back to the heart at low pressure; it has valves to stop the blood flowing backwards.
Markers reward: artery thick wall, small lumen, high pressure, carries blood from heart; vein thinner wall, larger lumen, valves, low pressure, carries blood to heart. Forgetting the valves in veins, or the direction of flow, are common errors.
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Sources & how we know this
- WJEC GCSE Biology specification (from 2016) — WJEC (2016)