thrombosis, embolism ischaemia infarction Flashcards
(29 cards)
what makes up blood?
A mixture of solid cells-
oxygen carrying red blood cells
infection fighting/ inflammatory white blood cells
clot forming platelets
in a liquid- plasma
Why are the formation of clots rare?
Two main factors:
1. Laminar flow
2. Endothelial cells
what stops us from bleeding to death if we cut ourselves?
clot- forming cells and proteins present in the blood
describe laminar flow
cells travel in the centre of arterial vessels and don’t touch the sides
how do endothelial cells decrease clot formation?
by lining vessels so they are not ‘sticky’ when healthy
describe thrombosis
it is the formation of a solid mass from blood constituents in an intact vessel in a living person
what is the first stage of thrombosis?
Platelet aggregation
describe the platelet aggregation stage
platelets release chemicals when they aggregate which causes other platelets to stick to them and also start off the cascade of clotting proteins in the blood.
these reactions involve positive feedback loops so that once they have started they are difficult to stop.
what forms once the clotting cascade has started?
the large protein molecule fibrin
what does fibrin make ?
a mesh in which red blood cells can become entrapped
what can cause thrombosis?
- a change in vessel wall
- a change in blood flow
- a change in blood constituents
( usually a combination of two or three of these)
give an example of a cause of thrombosis
e.g. endothelial cell injury by cigarette smoking causing endothelial cell injury (change in vessel wall and change in blood flow over the injured/absent cells)
If there is a high risk of thrombosis what measures would you take to prevent it?
(e.g. early mobilisation after operation, low dose subcutaneous heparin).
describe an embolism
it is the process of a solid mass in the blood being carried through the circulation to a place where it gets stuck and blocks the vessel
what is the most common solid mass in an embolism?
thrombus
(e.g. a deep venous thrombosis of the leg veins which breaks off and embolises through the large veins and right side of the heart to the lungs).
what are the less common causes of embolus?
- Air- be careful with pressurised systems of IV fluids/blood in infants and children
- Cholesterol crystals- from atheromatous plaques
- Tumour
- Amniotic Fluid
- Fat- severe trauma with multiple fractures
what happens if an embolus enters the venous system?
it will travel to the vena cava through the right side of the heart and will lodge somewhere in the pulmonary arteries- depending on size.
why can an embolus not get through to the arterial circulation?
the blood vessels in the lung split down to capillary size- so only RBC can fit through so the lungs act as a filter for any venous emboli
what acts as a filter for any venous emboli?
the lungs
describe ischaemia
is simply a reduction blood flow to a tissue without any other implications.
describe infarction
is the reduction in blood flow to a tissue that is so reduced that it cannot even support mere maintenance of the cells in that tissue so they die.
what usually causes infarction?
is usually a macroscopic event caused by thrombosis of an artery e.g. thrombus in the left anterior descending coronary artery causing infarction of the anterior wall of the left ventricle.
why are most organs susceptible to infarction?
as most organs have only a single artery supplying them- end arterial supply
