IB DP Biology: HL复习笔记6.3.2 Blood Clotting

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

• The chemical cascade, triggered by the clotting factors, involves a large number of steps and several plasma proteins
  • First of all, the clotting factors stimulate 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

Blood clot formation

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 ATPwhich 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