Double circulation

In the syllabus and the exam

Double circulation is used to explain why the human heart has two separate sides and why blood must return to the heart between the pulmonary and systemic circuits rather than travelling in one continuous loop. Candidates are expected to trace the full pathway, deoxygenated blood from the body enters the right atrium, is pumped by the right ventricle to the lungs, returns oxygenated to the left atrium, and is pumped by the powerful left ventricle around the rest of the body, and to name this as pulmonary circulation and systemic circulation respectively. A frequent higher-order question asks candidates to explain the advantage of double circulation compared with a single-circulation system found in fish, and the expected reasoning is that blood is re-pressurised after passing through the low-pressure lung capillaries, so it reaches body tissues at high pressure and can deliver oxygen more efficiently. A common mixed-up answer describes only one circuit or fails to explain why blood needs to pass through the heart twice.

Example

In double circulation, blood returning from the lungs passes through the heart again before being pumped out to the rest of the body.

Related terms

ArteryVeinHaemoglobin

Source:SRC-DSKP-EN