Atherosclerosis & blood clots Flashcards
What is atherosclerosis?
The disease process that leads to coronary heart disease and strokes
What happens in atherosclerosis?
Fatty deposits can either block an artery directly or increase its chance of being blocked by a blood clot (thrombosis). The blood supple can be blocked completely.
What happens if the blood supply is not restored very quickly?
The affected cells are permanently damaged. In the coronary arteries thus results in a heart attack. In the arteries supplying the brain it results in a stroke.
What is event 1 of atherosclerosis?
The endothelium becomes damaged and dysfunctional for some reason. This endothelial damage can result from high blood pressure, which puts an extra strain on the layer of cells.
What is event 2 of atherosclerosis?
Once the inner lining of the artery is breached there is an inflammatory response. WBC leave the blood vessel and move into the artery wall. These cells accumulate chemicals from the blood, particularly cholesterol. A fatty deposit builds up, an atheroma.
What is event 3 of atherosclerosis?
Calcium salts and fibrous tissue also build up at this site, resulting in a hard swelling called a plaque on the inner wall of the artery. The build-up of fibrous tissue means that the artery wall loses some of its elasticity; it hardens.
What is event 4 of atherosclerosis?
Plaques cause the lumen of the artery to become narrower. This makes it more difficult for the heart to pump blood around the body and can lead to a rise in blood pressure. Now there is a dangerous positive feedback building up. Plaques lead to a raised blood pressure and raised blood pressure makes it more likely that further plaques will form, as damage to endothelial tissue in other areas becomes more likely.
Why do only arteries get atherosclerosis?
The fast-flowing blood in arteries is under high pressure so there is a significant chance of damage to the walls
What does a blood clot do?
Seals the break in the blood vessel and limits blood loss and prevents entry of pathogens through any open wounds
What do platelets do when they come into contact with the damaged vessel wall?
Their cell surfaces change, causing them to stick to the exposed collagen in the wall and to each other to form a temporary platelet plug
How do blood clots form?
- Platelets and damaged tissue release thromboplastin
- Thromboplastin activates an enzyme that catalyses the conversion of prothrombin into thrombin. A number of other protein factors, vitamin K and calcium ions must be present in the blood plasma for this conversion to happen
- Thrombin then catalyses the conversion of the soluble plasma protein fibrinogen into the insoluble protein fibrin
- A mesh of fibrin forms that traps more platelets and RBC to form a clot
Why doesn’t blood usually clot in vessels?
Platelets do not stick to the endothelium of blood vessels, it is very smooth and has substances on its surface that repel the platelets
What happens in arteries to cause blood clotting?
If there is atherosclerosis and the endothelium is damaged, the platelets come into contact with the damaged surface and any exposed collagen. The clotting will be triggered.
What happens if the coronary arteries begin to narrow?
It limits the amount of oxygen-rich blood reaching the heart muscle. The result may be a chest pain called angina.
When is angina experienced?
During exertion when the cardiac muscle is working harder and needs to respire more. Because the heart muscle lacks oxygen, it is forced to respire anaerobically.
What happens if a fatty plaque in the coronary artery ruptured?
Collagen is exposed which leads to rapid clot formation. The blood supply to the heart may be blocked completely. The heart muscle supplied by these arteries does not receive any blood, so it is ischaemic. If the affected muscle cells are starved of oxygen for long they will be permanently damaged and a myocardial infarction occurs.
What happens if a blood clot blocks one of the arteries leading to the brain?
A full stroke will result. If brain cells are starved of oxygen for more than a few minutes they will be permanently damaged and it can be fatal.
