• Blood clotting is an important process; it prevents excess blood loss, the entry of pathogens, and provides a barrier, or scab, under which wound healing can occur
• A break in the mucous membranes or skin membranes causes the release of molecules that trigger a?chemical cascade?which results in blood clotting
  • The process of blood clotting is known as?thrombosis
• The chemical cascade involves a large number of steps and several plasma proteins

• The process of thrombosis involves
  • ?The damaged blood vessel releases a protein called?thromboplastin
  • Calcium ions?from the plasma, along with thromboplastin, trigger the conversion of soluble?prothrombin?protein into the enzyme?thrombin
  • Thrombin?catalyses the conversion of the?soluble protein?fibrinogen?to the?insoluble protein fibrin
  • Fibrin fibres mesh and tangle together,?trapping platelets and red blood cells
  • A blood clot is formed

Blood clotting, or thrombosis, is brought about by a cascade of chemical reactions

Blood clots and atheromas

• Atheromas?can?increase the risk?of?blood clotting
  • The?plaque deposit?of an atheroma can?rupture through the endothelium?of the artery,?damaging the endothelium and forming a rough surface
  • The damage to the endothelium triggers the process of thrombosis
• The combination of atheromas and blood clotting can be dangerous to the health of an individual
  • The blood clot that forms can?completely block the artery
    • Blood clots reduce blood flow which?restricts the movement of oxygen?in the blood, therefore?reducing respiration?of the surrounding?cells, tissues and organs
  • The blood clots can dislodge and travel to different blood vessels in the body; if they reach the brain this can cause a?stroke?to occur
• Blood clotting can also lead to
  • Heart attack
  • Deep vein thrombosis

Stroke

• A stroke is a?sudden loss of brain function?in a localised area due to?disruption of blood flow?to the brain
  • A blood clot leads to a?blockage of the arteries?supplying the brain
  • This leads to?reduced blood flow and delivery of oxygen?to the cells of the brain, reducing respiration
  • Cells in the affected part of the brain cannot produce ATP and their function is reduced
• A stroke caused by a blood clot is called an?ischemic stroke

Heart attack

• Coronary heart disease (CHD)?is caused by the formation of atheromas and blood clots in the?coronary arteries
  • The coronary arteries flow over the surface of the heart, supplying the heart muscle itself with blood
• Blood flow to certain areas of the heart is restricted?and delivery of oxygen to the affected cells decreases, thereby?reducing respiration?in these cells
  • The cells can no longer produce ATP
  • The cells can no longer contract,?reducing the force generated by the heart?when it beats
  • The cells can die, causing permanent damage to heart tissue
• This leads to a?myocardial infarction,?also known as a heart attack
• Complete heart failure?may occur if large areas of the heart are affected by blood clots; this can be fatal
• Symptoms?of a heart attack include
  • Chest pain
  • Shortness of breath
  • Sweating

Atheroma and blood clots in the coronary arteries can restrict blood flow to the heart muscle, leading to a heart attack

Deep vein thrombosis

• If a blood clot forms in a vein deep inside the body, it is known as?deep vein thrombosis (DVT)
• This is most common in the?veins of the legs
• Causes include
  • Prolonged inactivity
  • Old age
  • Some medications