state that the mammalian circulatory system is a closed double circulation consisting of a heart, blood and blood vessels including arteries, arterioles, capillaries, venules and veins
Cambridge A-Level Biology – The Circulatory System
The Circulatory System
Learning Objective
State that the mammalian circulatory system is a closed double circulation consisting of a heart, blood and blood vessels including arteries, arterioles, capillaries, venules and veins.
Key Features
Closed system: Blood remains within vessels at all times.
Double circulation: Separate pulmonary and systemic circuits.
Components: Heart, blood, blood vessels.
Components of the System
Component
Function / Description
Heart
A muscular pump that drives blood through the two circuits.
Blood
Transport medium for gases, nutrients, waste products and hormones.
Arteries
Thick‑walled vessels that carry blood away from the heart under high pressure.
Arterioles
Small branches of arteries that regulate blood flow into capillary beds.
Capillaries
Microscopic vessels where exchange of gases, nutrients and wastes occurs.
Venules
Small vessels that collect blood from capillaries and merge into veins.
Veins
Thin‑walled vessels that return blood to the heart under low pressure.
Path of Blood Through Double Circulation
Deoxygenated blood enters the right atrium of the heart.
It is pumped into the right ventricle and then to the lungs via the pulmonary artery.
In the lungs, blood becomes oxygenated and returns to the left atrium via the pulmonary veins.
The left ventricle pumps oxygen‑rich blood into the aorta, distributing it through the systemic circuit.
Blood passes through arteries, arterioles, capillaries (exchange), venules and veins back to the right atrium.
Suggested diagram: Schematic of the mammalian double circulatory system showing heart chambers, pulmonary and systemic circuits, and the major types of blood vessels.