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First teaching 2014

Last exams 2024

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Blood Clotting (DP IB Biology: SL)

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Platelets

  • When the skin is cut, microorganisms have an entry point to get into the body
    • The first line of defence is compromised

  • In order to minimise the risk of substantial blood loss and entry of unwanted microorganisms, the blood starts to clot to seal the wound
  • In response to blood vessel damage, platelets form a temporary plug to stem bleeding
    • Platelets are cellular fragments that make up one component of the blood

  • They release chemicals called clotting factors that trigger a chemical cascade which results in blood clotting

The components of the blood 1, downloadable IGCSE & GCSE Biology revision notes

The blood is made up of 4 key components including plasma, red blood cells, white blood cells and platelets

Blood Clotting Proteins

  • The chemical cascade, triggered by the clotting factors, involves a large number of steps and several plasma proteins
    • First of all, the clotting factors activate the process which stimulates the release of the enzyme thrombin
    • Thrombin catalyses the conversion of the soluble protein fibrinogen into fibrin, which is insoluble
    • Fibrin forms a mesh that traps more platelets and blood cells to prevent entry through the wound
      • A small initial stimulus is amplified to produce a large amount of fibrin so that the wound is quickly sealed

    • Exposure to air results in the hardening of the mesh to create a scab

Clotting factors and blood clot formation 1, downloadable IB Biology revision notesClotting factors and blood clot formation 2, downloadable IB Biology revision notesClotting factors and blood clot formation 3, downloadable IB Biology revision notes

Blood clot formation

Clotting in Coronary Arteries

Causes of blood clots in the coronary arteries

  • A blood clot in the coronary arteries is called coronary thrombosis
  • Several factors may increase the risk of coronary thrombosis developing:
    • Atherosclerosis in the coronary arteries results in a build-up of layers of fatty material (plaque) causing damage to the endothelium wall
      • Bulging of the lumen of the artery causes a blockage which reduces the space for blood flow
      • Deposition of calcium ions can worsen the situation by hardening the endothelium
      • Lesions can also sometimes form due to ruptures in the atheroma

Consequences of blood clot formation in the coronary arteries

  • Occlusion of the coronary arteries is a common problem that can lead to significant health issues such as coronary heart disease
  • The coronary arteries deliver oxygen and nutrients to the cardiac muscle tissue
  • If a blood clot forms in the coronary arteries, it can cause blockages
  • A blockage means that the tissue beyond that point is deprived of oxygen and nutrients, so it is unable to respire aerobically
  • As a result, cells are unable to produce a sufficient amount of ATP which inhibits normal cardiac muscle contraction resulting in irregular and uncoordinated movement called fibrillation
    • If not rectified, either naturally or through medical intervention, fibrillation could lead to death

  • A heart attack (myocardial infarction) may also occur in situations where the blood supply is completely inhibited so that the cardiac muscle tissue starts to die
    • This can be fatal

Risk factors for coronary thrombosis

  • There are several factors which have shown a clear correlation with increased chances of coronary thrombosis or heart attacks
  • The main risk factors for include:
    • Genetic factors
    • Age and sex
    • High blood pressure
    • Smoking
    • High concentrations of low-density lipoproteins (LDLs) 
    • Diabetes
    • Obesity
    • Lack of exercise

Examiner Tip

Remember, correlation does not prove causation: There are many contributing factors which will affect the likelihood of developing a coronary thrombosis, as a result, we cannot say that any single factor is causative. We can say that there is a correlation between that factor and the incidence of coronary thrombosis

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Ruth

Author: Ruth

Expertise: Biology

Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. She gained 10 years of teaching experience across the 3 key science disciplines and physical education. Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.