Blood clotting - AS OCR F221


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A simple view of blood clotting. Suitable for OCR AS module F221.

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Blood clotting - AS OCR F221

  1. 1. Preventing blood loss
  2. 3. <ul><li>When a blood vessel is damaged </li></ul><ul><li>Bleeding occurs </li></ul><ul><li>A cascade of reactions occur in the blood </li></ul><ul><li>A blood clot forms to stop continued blood loss </li></ul>
  3. 4. Excessive bleeding – what do you do?
  4. 5. Seek medical help – but while you’re waiting..... <ul><li>If possible put on some disposable gloves </li></ul><ul><li>Reassure the person – get them to sit / lie down </li></ul><ul><li>Look carefully at the wound – it might be necessary to cut the clotting away to see it clearly, e.g. make sure there is no glass there. </li></ul><ul><li>If there is nothing in the wound, place a large pad of clean cloth onto the wound and press it down firmly using your hand. </li></ul><ul><li>Use a bandage to hold the pad in place </li></ul>
  5. 6. If there is an object stuck in the wound.. <ul><li>Don’t remove it! </li></ul><ul><li>Make a pad in the shape of a ring and place it on the wound so that it surrounds the object </li></ul><ul><li>Use a bandage to apply pressure on the ring around the sides of the wound. The pressure should push the edges of the wound together. </li></ul><ul><li>If the wound is in an arm or leg, raise it higher. </li></ul><ul><li>If the blood soaks through the first pad, don’t remove it but put another on top. </li></ul>
  6. 7. How blood clots
  7. 8. The actual process.. <ul><li>When tissues are damaged they are exposed to the air. Collagen fibres (in the connective tissue) are exposed and platelets stick to them. </li></ul><ul><li>The platelets release a substance that makes them sticky, the platelets clump together to form a plug – this forms an initial barrier. Calcium is needed for this process. </li></ul><ul><li>Leucocytes collect at the site and the </li></ul><ul><li>exposed tissues just below the </li></ul><ul><li>endothelium release an enzyme </li></ul><ul><li>called thromboplastin . </li></ul>
  8. 9. <ul><li>Platelets also break down and release thromboplastin. </li></ul><ul><li>Thromboplastin catalyses the conversion of an inactive plasma protein , prothtrombin into thrombin. This reaction also requires calcium ions. </li></ul><ul><li>Thrombin is an active enzyme. It hydrolyses a large soluble plasma protein called fibrinogen into smaller units. </li></ul><ul><li>The smaller units join together (polymerise) to form long, insoluble fibres of fibrin (a protein) </li></ul><ul><li>This process also requires calcium ions. </li></ul><ul><li>The fibrin fibres pile up and form a mesh over the wound. Blood cells become trapped in the mesh and form a blood clot. The clot dries to form a scab, this prevents further blood loss. It also stops pathogens getting into the wound. </li></ul>
  9. 10. Thrombin <ul><li>Thrombin is an enzyme </li></ul><ul><li>Enzymes are proteins that catalyse a specific reaction in the body. </li></ul><ul><li>It does this by reducing the activation energy needed for the reaction to occur. </li></ul>
  10. 11. Enzyme facts <ul><li>They are globular proteins with a highly specific tertiary structure. </li></ul><ul><li>Enzymes have an active site. This is exactly the right shape for one specific substrate to fit in. It works like a key fits into a lock. </li></ul><ul><li>An enzyme-substrate complex is formed. Due to the very close fit the enzyme exerts forces on the substrate and the activation energy required is lowered. </li></ul><ul><li>After the reaction has taken place, the enzyme is unchanged and can be used over and over again. </li></ul>
  11. 12. What affects enzyme activity? <ul><li>Enzyme concentration: low concentration = low rate of reaction. For the rate of reaction to remain high there also needs to be a constantly high concentration of substrate molecules. </li></ul>Fixed concentration of substrate If substrate concentration is also increased