Why do humans have a double circulatory system?
Humans have a double circulatory system so blood can be pumped to the lungs and to the body at high pressure, delivering oxygen quickly to meet high energy demands.
GCSE Biology
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In more detail
In a double circulatory system blood passes through the heart twice for each full circuit. One loop pumps blood to the lungs to pick up oxygen (and drop off CO₂); the other pumps oxygenated blood around the rest of the body. Because the blood is re-pressurised by the heart before going to the body, it travels faster and at higher pressure than a single circuit, delivering oxygen and glucose to respiring cells quickly — essential for warm-blooded animals with a high metabolic rate.
Key points for the exam
- One loop: heart → lungs → heart (gas exchange).
- Other loop: heart → body → heart (delivery).
- Re-pressurising the blood means higher pressure and faster delivery of oxygen.
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