The blood

• Main components of blood

  • Red blood cells
  • White blood cells
  • Platelets
  • Plasma
• Red blood cells


  Carry oxygen from the lungs to the body's tissues
• Red blood cells


  • Don't have a nucleus, which means more space for hemoglobin and oxygen
  • Shaped like a biconcave disc, which gives them a large surface area for absorbing oxygen
• White blood cells


  An essential part of the immune system, which defends against infection
• Functions of white blood cells

  • Phagocytosis (engulfing and consuming microorganisms)
  • Producing antibodies that bind to and help destroy pathogens
  • Producing antitoxins that neutralize toxins produced by pathogens
• Platelets


  Small fragments of cells that float in the blood and help stop bleeding by forming clots
• Plasma


  The liquid part of the blood that carries various substances, including red blood cells, white blood cells, and platelets
• Most adults have about 5 liters of blood flowing through their circulatory system at any one time
• Artificial blood


  A blood substitute that consists of salt water, which adds volume to the circulatory system but does not contain red blood cells and cannot transport oxygen
• Blood transfusion


  Giving a person real blood that has been donated by blood donors, which contains red blood cells and can help replace blood lost due to injury or surgery
• Blood plasma


  The liquid part of the blood
• Functions of blood plasma

  1. Transports dissolved substances around the body

  2. Transports soluble digestion products from small intestine to other organs

  3. Transports carbon dioxide from body cells to lungs

  4. Transports waste product urea from liver to kidneys
• Red blood cells


  • Contain the oxygen-carrying molecule hemoglobin
  • Have no nucleus, allowing more space for hemoglobin
  • Have a biconcave disk shape, increasing surface area for oxygen diffusion
• Function of red blood cells

  Transport oxygen from lungs to body cells
• White blood cells


  • Part of the immune system, e.g. making antibodies
  • Contain a nucleus with DNA encoding instructions
• Platelets


  Tiny fragments of cells that help the blood to clot
• Uses of donated blood

  • Replace blood loss during injury
  • Platelets extracted to help clotting
  • Proteins extracted, e.g. antibodies
• Blood transfusion


  Donated blood must be the same blood type as the patient, otherwise the body's immune system will reject it
• Blood in the UK is screened for infection, so the risk of transmission is extremely low