How does the double circulatory system move blood around the body?
The double circulatory system, the structure and function of arteries, veins and capillaries, how each blood vessel is adapted to its job, and the effect of lifestyle on the circulatory system including coronary heart disease.
A focused CCEA GCSE Biology answer on the circulatory system, covering the double circulation, the structure and adaptations of arteries, veins and capillaries, and how lifestyle factors affect the circulatory system and cause coronary heart disease.
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What this dot point is asking
CCEA wants you to describe the double circulatory system, explain the structure and function of arteries, veins and capillaries and how each is adapted, and explain how lifestyle factors affect the circulatory system and cause coronary heart disease.
The double circulatory system
This double system keeps oxygenated and deoxygenated blood separate and lets the blood be pumped to the body at high pressure, which is efficient for active mammals.
The blood vessels
| Vessel | Direction | Wall | Lumen | Valves |
|---|---|---|---|---|
| Artery | Away from heart | Thick, muscular, elastic | Narrow | No |
| Vein | Back to heart | Thin | Wide | Yes |
| Capillary | Between them | One cell thick | Very narrow | No |
How each vessel is adapted
Arteries have thick elastic walls to withstand high pressure and recoil to smooth the flow. Veins have valves because the low-pressure blood could otherwise flow backwards. Capillaries have walls one cell thick so oxygen, glucose and carbon dioxide can diffuse quickly between blood and cells.
Examples in context
Example 1. Why the heart has its own blood supply. The heart is a muscle that respires constantly, so it needs its own oxygen supply, delivered by the coronary arteries. If these arteries narrow with fatty deposits, the heart muscle gets too little oxygen, causing chest pain (angina) or, if a coronary artery is blocked, a heart attack. This is why coronary heart disease is so serious and why diet, exercise and not smoking matter for heart health.
Example 2. Lifestyle and the circulatory system. A diet high in saturated fat raises blood cholesterol, which builds up as plaques narrowing the arteries. Smoking damages the artery lining and the carbon monoxide reduces the oxygen the blood carries, while a lack of exercise and high blood pressure add further strain. Together these lifestyle factors increase the risk of coronary heart disease and strokes. CCEA often asks you to link several of these factors to their effects, so learn the chain from cause to consequence.
Try this
Q1. Which blood vessel carries blood away from the heart? [1 mark]
- Cue. An artery.
Q2. Explain why capillary walls are only one cell thick. [2 marks]
- Cue. So substances such as oxygen and glucose can diffuse quickly between the blood and the cells.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA 20214 marksExplain how the structure of an artery is adapted to its function.Show worked answer →
Four marks for adaptations linked to carrying blood at high pressure.
Arteries carry blood away from the heart at high pressure, so they have thick, muscular and elastic walls that can withstand and maintain the pressure.
The elastic walls stretch when the heart beats and recoil between beats, which smooths the blood flow and keeps the pressure up.
They have a relatively narrow lumen (central space), which helps keep the pressure high.
Markers reward thick muscular and elastic wall, withstands high pressure, elastic recoil, narrow lumen. Veins, by contrast, have thin walls, a wide lumen and valves.
CCEA 20194 marksExplain how an unhealthy lifestyle can lead to coronary heart disease.Show worked answer →
Four marks for the cause, the effect on the coronary arteries and the result.
A diet high in saturated fat and cholesterol can cause fatty deposits (plaques) to build up in the walls of the coronary arteries.
This narrows the coronary arteries, reducing the blood flow and so the oxygen supply to the heart muscle.
Smoking and high blood pressure make this worse and increase the risk.
If a coronary artery becomes blocked, part of the heart muscle is starved of oxygen and a heart attack occurs.
Markers reward fatty deposits narrowing the coronary arteries, reduced oxygen to the heart muscle, and the link to a heart attack.
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Sources & how we know this
- CCEA GCSE Biology specification — CCEA (2017)