Blood

• Blood is a tissue consisting of plasma, in which red blood cells, white blood cells, and platelets are suspended
• Red blood cells:

  • The red blood cells have a biconcave shape to give them a large surface area to volume ratio. Their only function is to transport oxygen
  • They are filled with haemoglobin, an iron-containing protein, that combines with oxygen.
  • They have no nucleus, making more space for haemoglobin
• White blood cells:

  • White blood cells help protect the body from infection
  • Some (lymphocytes) produce antibodies to destroy pathogens
  • Other (phagocytes) engulf invadingbacteria and viruses
• Platelets:

  • Platelets are small fragments of cells
  • They help clot blood at a site of a wound
  • Blood clotting is a series of enzyme-controlled reactions that result in converting fibrinogen (soluble) into fibrin (insoluble)
  • This produces a network of protein fibre which captures red blood cells and platelets to form a clot.
  • The clot develops into a scab, which prevents the entry of pathogens (bacteria)
• Plasma:

  • Plasma is the only liquid part of the blood
  • It is made of mainly of water with dissolved substances such as glucose, CO2, urea and hormones.
  • Urea is formed in your liver from the breakdown of excess proteins and is carried to your kidneys where it is removed in urine
  • The small soluble products of digestion pass into the plasma from your small intestine and are transported to individual cells.