Blood’s double journey

The heart pumps blood around two circuits.

BODY → RIGHT SIDE OF HEART → LUNGS

At the lungs: blood gains oxygen and loses carbon dioxide.

LUNGS → LEFT SIDE OF HEART → BODY

At body cells: blood delivers oxygen and nutrients.

ARTERIES carry blood away from the heart.

VEINS carry blood towards the heart.

CAPILLARIES allow exchange with cells.

Valves help prevent blood flowing backwards.

Colours show oxygen level. Blood is red.

The right and left sides shown belong to the same heart. Blue shows lower oxygen levels; red shows higher oxygen levels.