Circulatory System

• Plasma

  Description: The liquid part of blood

  Function: Responsible for transport of blood cells, absorbed food molecules, carbon dioxide, hormones and urea.
• Red Blood Cells

  Description:

  • Contain Haemoglobin which is rich in iron, that carries oxygen.
  • Biconcave shape provides large surface area for oxygen diffusion.
  • No nucleus- more space for oxygen diffusion.

  Function: Carry oxygen around the body.
• White Blood Cells

  Description: Phagocytes engulf and digest microorganisms during a process called phagocytosis. Lymphocytes produce antibodies.

  Function: 2 types, both defend against diseases.
• Platelets

  Description: Very small structures

  Function: Important in blood clotting and formation of scabs. Converting protein fibrinogen to fibrin forms mesh network that traps other blood components.
• Arteries

  • Carry blood away from the heart.
  • Carry oxygenated blood.
  • Have a thick layer of muscle and many elastic fibres,
  • Small lumen inside for blood to flow.
  • Blood flows at high pressure due to action of the heart.
• Capillaries:

  • Connect arteries and veins.
  • Carry both oxygenated and deoxygenated blood,
  • Walls only one cell thick.
  • Lumen diameter of a red blood cell.
  • Low blood pressure and slow speed to allow exchange of materials.
• Veins

  • Carry blood back to the heart.
  • Carry deoxygenated blood.
  • Thin layer of muscle and few elastic fibres.
  • Large lumen inside for blood to flow.
  • Blood flows at low pressure.
  • Have valves to stop the backflow of blood.
• Double circulation - Blood travels through the heart twice in one circulation.
• If someone exercises more, when they’re at rest:

  1. Heart muscle will be stronger,
  2. Cardiac output increased,
  3. Pulse rate reduced.