thrombosis, embolism, ischaemia & infarction

Question 1

why dont blood clots form all the time

Answer 1

because there is a mixture of solid cells (red blood cells/ white blood cells/ platelets) in a liquid (plasma) which rushes around a complicated system of pipes which have lots of curves and changes in diameter.

Question 2

what 2 reasons make blood clots rare

Answer 2

1. Laminar flow – cells travel in the centre of arterial vessels and don’t touch the sides

2.Endothelial cells which line vessels are not ‘sticky’ when healthy

Question 3

why are clot-forming cells and proteins are present in the blood

Answer 3

to stop us bleeding to death if we cut or scratch ourselves.

Question 4

define thrombosis

Answer 4

solid mass of blood constituents formed within intact vascular system during life

Question 5

5 steps of thrombus formation

Answer 5

1. Damage to endothelial cells in the vessel causes some of the cells to lift away from the vessel wall, exposing collagen.
2. Platelets then begin to stick to this exposed collagen, and release the chemicals which cause platelet aggregation. Platelet aggregation also starts off the cascade of clotting proteins in the blood.
3. Red blood cells then get trapped within the aggregating platelets
4. Clotting factors join the red blood cells and platelets, and the clotting cascade forms a large protein molecule fibrin, which then gets deposited and forms the clot.
5. Positive feedback loop -> can end up causing a thrombus (thrombosis), blocking the artery

Question 6

3 causes of thrombosis

Answer 6

Change in vessel wall
Change in blood flow
Change in blood constituents

Question 7

how can you reduce risk of thrombosis

Answer 7

Low dose aspirin inhibits platelet aggregation, so this can be prescribed to reduce the risk of thrombosis.

Question 8

define embolism

Answer 8

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

solid mass - most likely thrombus

Question 9

define embolus

Answer 9

mass of material in the vascular system able to become lodged within a vessel and block it

Question 10

main cause of embolus

Answer 10

Usually caused by a part of a thrombus that has broken off and circulates in the blood stream (only small vessels can become blocked).

Question 11

less common causes of embolus (4)

Answer 11

Air (pressurised systems of intravenous fluids/ bloods)

Tumour

Amniotic fluid (rare in pregnant women)

Fat (severe trauma with fractures)

Question 12

what happens if an embolus enters the venous system

Answer 12

it will travel to the vena cava and lodge in the pulmonary arteries.
The lungs then act as a filter for venous emboli, because the blood vessels split down to capillary size, which is too small for the embolus to travel through.

Question 13

what happens if an embolus enters the arterial system

Answer 13

it can travel anywhere downstream of its entry point.

Question 14

define ischaemia

Answer 14

reduction of blood flow to a tissue without any other implications

Question 15

define infarction

Answer 15

a reduction of 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

Question 16

what usually causes infarction

Answer 16

macroscopic event

caused by thrombosis of an artery

Question 17

define end artery supply

Answer 17

an organ that only receives blood supply from one artery.

most organs are like this

so they are v susceptible to to infarction

Question 18

when are end arterial supplies problematic

Answer 18

when a thrombus forms, because the whole blood supply to that organ is cut off leading to infarction.

Question 19

impact of dual/multiple artery supply

Answer 19

these organs can survive if a thrombus occurs in one arterial supply.

Question 20

3 examples of multiple artery supply

Answer 20

Pulmonary arteries and bronchial arteries supplying the lungs

Portal vein and hepatic artery supplying the liver

Some parts of the brain – circle of Willis

Question 21

define atheroma

Answer 21

degeneration of the walls of the arteries caused by accumulated fatty deposits and scar tissue, and leading to restriction of the circulation and a risk of thrombosis.