Circulatory System (SQA National 5 Biology): Revision Note

The circulatory system

• The circulatory system is an organ system, the role of which is to transport blood around the body

• The circulatory system consists of a closed network of blood vessels connected to the heart

  • Oxygenated blood is carried away from the heart to the respiring tissues via the arteries

  • Arteries narrow to arterioles and then to capillaries as they pass through the organ

    • In the organs, respiring cells use up the oxygen from the blood

  • The capillaries widen to venules and finally to veins as they move away from the organs

  • Veins carry deoxygenated blood back towards the heart

  • The blood is then pumped to the lungs to collect oxygen before returning to the heart to be pumped to the body once again