The Heart and Blood Vessels

The heart is the organ at the centre of the circulatory system, pumping blood around the body to deliver oxygen and nutrients and remove waste products. This lesson covers the structure of the heart, the double circulatory system, and the three types of blood vessel — all as required by the AQA GCSE Combined Science Trilogy specification (8464).

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The Double Circulatory System

Mammals, including humans, have a double circulatory system. This means that blood passes through the heart twice during each complete circuit of the body.

graph LR
    subgraph "Circuit 1 — Pulmonary"
        H1["Right side of heart"] -->|"Deoxygenated blood"| L["Lungs"]
        L -->|"Oxygenated blood"| H2["Left side of heart"]
    end
    subgraph "Circuit 2 — Systemic"
        H2 -->|"Oxygenated blood"| B["Body tissues"]
        B -->|"Deoxygenated blood"| H1
    end

Circuit	Name	Blood Flow	Purpose
Circuit 1	Pulmonary circulation	Heart → lungs → heart	Blood picks up oxygen and releases carbon dioxide
Circuit 2	Systemic circulation	Heart → body → heart	Blood delivers oxygen and nutrients to cells and removes waste