Blood

• Blood is a tissue because it is a collection of similar specialised cells that serve particular functions
• Blood


  Made in the bone marrow of long bones, process is called haemopoiesis
• Red blood cells (erythrocytes)

  • No nucleus - they lose it during their development so they can pack in more haemoglobin
  • Biconcave shape - to maximise their surface area for oxygen absorption
  • Small and flexible so that they can fit through narrow blood capillaries
  • Thin - there is only a short distance for the oxygen to diffuse to reach the center of the cell
  • Haemoglobin - which gives them their red colour
• Haemoglobin


  Can combine reversibly with oxygen, important as it can combine with oxygen as blood passes through the lungs and release the oxygen when it reaches the cells
• Types of white blood cells

  • Phagocytes
  • Lymphocytes
• Phagocytes


  About 70 per cent of white blood cells, engulf and destroy unwanted microorganisms that enter the blood, by the process of phagocytosis, part of the body's immune system
• Lymphocytes


  Make up about 25 per cent of white blood cells, part of the body's immune system, produce soluble proteins called antibodies when a foreign body such as a microorganism enters the body
• Platelets


  Cell fragments produced by giant cells in the bone marrow, stop bleeding in two main ways: they have proteins on their surface that enable them to stick to breaks in a blood vessel and clump together, and they secrete proteins that result in a series of chemical reactions that make blood clot, which plugs a wound
• Blood components


  • Red blood cells
  • White blood cells
  • Platelets
  • Plasma
• Staining gives colour to the cells, like the nucleus and granules, making the cells more visible and easier to identify, count and differentiate
• Blood transfusion


  Blood for transfusion must be compatible with that of the patient's blood, for instance, their blood group, and white blood cells are often removed to reduce the risk of infections or immune reactions
• Antigens


  Proteins on the surface of blood cells that determine blood type
• Antibodies


  Found in the blood, cause agglutination (clumping) if the wrong type of blood is given
• If someone is given the wrong type of blood, clumps form - agglutination
• Agglutination is when blood cells clump