B2 - Blood

• Blood


  Consists of 4 main things: red blood cells, white blood cells, platelets, and plasma
• Red blood cells (RBCs)

  • Make up almost half of blood by volume
  • Carry oxygen from lungs to body tissues
  • Contain hemoglobin which binds to oxygen
  • Lack a nucleus to allow more space for hemoglobin
  • Shaped like biconcave discs for large surface area
• White blood cells


  • Make up less than 1% of blood
  • Essential part of immune system
  • Defend against infection through phagocytosis, antibody production, and antitoxin release
  • Have a nucleus unlike RBCs
• Platelets


  • Not actual cells, but small cell fragments
  • Float in blood and rush to wounds to help clot blood and stop bleeding
  • Also help prevent microorganisms from entering through wounds
• Plasma


  • Makes up over half of blood volume
  • Pale straw-colored liquid that makes blood watery and able to flow
  • Carries RBCs, WBCs, platelets, nutrients, waste, hormones, antibodies, and toxins
• Most adults have about 5 liters of blood in their circulatory system
• Blood replacement


  1. Artificial blood (blood substitute) - adds volume but lacks oxygen-carrying RBCs

  2. Blood transfusion - uses donated real blood with RBCs to replace lost blood and oxygen-carrying capacity