The Heart and Circulatory System

The circulatory system is the organ system responsible for transporting substances around the body in the blood. For AQA GCSE Biology, you need to understand the structure of the heart, how it pumps blood, the difference between the two circulation loops, and the role of key blood vessels. The human circulatory system is described as a double circulatory system because the blood passes through the heart twice during each complete circuit of the body.

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The Double Circulatory System

Humans have a double circulatory system, meaning the blood flows through two separate circuits:

graph LR
    A[Right Side of Heart] -->|Pulmonary artery| B[Lungs]
    B -->|Pulmonary vein| C[Left Side of Heart]
    C -->|Aorta| D[Body — Organs and Tissues]
    D -->|Vena cava| A