The blood

• Components of blood


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


  Tiny disc shaped cells that transport oxygen throughout the body, have no nuclei or organelles, cytoplasm contains hemoglobin
• Oxygen transport by red blood cells


  1. In lungs, oxygen concentration is high, hemoglobin combines with oxygen forming oxyhemoglobin

  2. In places where oxygen concentration is low, oxygen dissociates from hemoglobin and diffuses into the cells down a concentration gradient
• White blood cells


  Help protect the body against disease-causing pathogens like bacteria and viruses, some are involved in phagocytosis, others produce antibodies
• White blood cells


  • Have a large nucleus that can be clearly seen under the microscope, typically around twice the size of red blood cells
• Platelets


  Small colorless cell fragments that cause the blood to clot whenever a blood cell is damaged
• Plasma


  The liquid component of the blood, made predominantly of water, makes up around 55% of total blood volume, transports mineral ions, carbon dioxide, nutrients, hormones, antibodies, urea
• Phagocytes


  • Have an irregular kidney-shaped nucleus, cytoplasm extends outwards when ingesting foreign particles, engulf and sometimes digest bacteria, cell debris, and other harmful substances by phagocytosis
• Lymphocytes


  • Much smaller white cells with a large spherical nucleus, one of the main functions is to produce antibodies which bind to pathogens and destroy them or mark them for destruction by phagocytes
• Blood clotting


  1. Platelets clump together to block the smaller capillaries and release a substance that acts on a soluble protein in the plasma called fibrinogen

  2. Fibrinogen is converted into the insoluble molecule fibrin which forms a branching network across the wound

  3. Red blood cells are trapped in the network forming a clot that stops further blood loss and prevents pathogens from entering the bloodstream