Cambridge O Level Biology · Syllabus 5090 · Transport in Humans
Circulatory System
What is Circulatory System?
The human circulatory system is a transport system made of a muscular pump (the heart), a branching network of blood vessels (arteries, capillaries and veins) and the blood itself, with one-way valves that keep blood flowing in a single direction. It carries oxygen, carbon dioxide, glucose, amino acids, ions, hormones, urea, blood cells and heat between the exchange surfaces of the body and every living cell.
This definition is part of the Transport in Humans chapter in Cambridge O Level Biology.
Circulatory System in context
The human circulatory system is a muscular pump (the heart), a network of blood vessels and the blood itself, with one-way valves that keep blood moving in a single direction. Blood passes through the heart twice during one complete circuit of the body, which is what makes the system a double circulation: a low-pressure pulmonary circuit to the lungs and a high-pressure systemic circuit to the rest of the body.