thrombosis, embolism ischaemia infarction

Question 2

what makes up blood?

Answer 2

A mixture of solid cells-
oxygen carrying red blood cells
infection fighting/ inflammatory white blood cells
clot forming platelets
in a liquid- plasma

Question 3

Why are the formation of clots rare?

Answer 3

Two main factors:
1. Laminar flow
2. Endothelial cells

Question 4

what stops us from bleeding to death if we cut ourselves?

Answer 4

clot- forming cells and proteins present in the blood

Question 5

describe laminar flow

Answer 5

cells travel in the centre of arterial vessels and don’t touch the sides

Question 6

how do endothelial cells decrease clot formation?

Answer 6

by lining vessels so they are not ‘sticky’ when healthy

Question 7

describe thrombosis

Answer 7

it is the formation of a solid mass from blood constituents in an intact vessel in a living person

Question 8

what is the first stage of thrombosis?

Answer 8

Platelet aggregation

Question 9

describe the platelet aggregation stage

Answer 9

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.

Question 10

what forms once the clotting cascade has started?

Answer 10

the large protein molecule fibrin

Question 11

what does fibrin make ?

Answer 11

a mesh in which red blood cells can become entrapped

Question 12

what can cause thrombosis?

Answer 12

1. a change in vessel wall
2. a change in blood flow
3. a change in blood constituents
   ( usually a combination of two or three of these)

Question 13

give an example of a cause of thrombosis

Answer 13

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)

Question 14

If there is a high risk of thrombosis what measures would you take to prevent it?

Answer 14

(e.g. early mobilisation after operation, low dose subcutaneous heparin).

Question 15

describe an embolism

Answer 15

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

Question 16

what is the most common solid mass in an embolism?

Answer 16

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).

Question 17

what are the less common causes of embolus?

Answer 17

1. Air- be careful with pressurised systems of IV fluids/blood in infants and children
2. Cholesterol crystals- from atheromatous plaques
3. Tumour
4. Amniotic Fluid
5. Fat- severe trauma with multiple fractures

Question 18

what happens if an embolus enters the venous system?

Answer 18

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.

Question 19

why can an embolus not get through to the arterial circulation?

Answer 19

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

Question 20

what acts as a filter for any venous emboli?

Answer 20

the lungs

Question 21

describe ischaemia

Answer 21

is simply a reduction blood flow to a tissue without any other implications.

Question 22

describe infarction

Answer 22

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.

Question 23

what usually causes infarction?

Answer 23

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.

Question 24

why are most organs susceptible to infarction?

Answer 24

as most organs have only a single artery supplying them- end arterial supply

Question 25

which organs have a dual arterial supply?

Answer 25

1. liver
2. lungs
3. brain

Question 26

what is the livers dual arterial supply?

Answer 26

portal venous and hepatic artery

Question 27

what is the lungs’ dual arterial supply?

Answer 27

pulmonary venous and hepatic artery

Question 28

what is the brains dual arterial supply?

Answer 28

around the circle of Wills with multiple arterial supplies

Question 29

describe atheroma

Answer 29

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.