Thrombosis and Infarction Flashcards Preview

Phase 2a - Introductory Clinical Sciences > Thrombosis and Infarction > Flashcards

Flashcards in Thrombosis and Infarction Deck (37)
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1

what two factors prevent blood clotting unnecessarily?

1. laminar flow - cells travel in centre of arterial vessels, and don't touch the sides
2. endothelial cells which line vessels are not 'sticky' when healthy

2

describe basic clot formation

coagulation cascade results in formation of a fibrin meshwork that entraps the cells into a solid but elastic clot
commonly form after death

3

what is a thrombus?

a solid mass of blood constituents formed within an intact vessel in life

4

what 3 things make up Virchow's triad?

abnormalities of vessel wall; abnormalities of blood flow; abnormalities of blood constituents

5

why do we need clot-forming cells and proteins in the blood?

to stop massive haemorrhage if we cut/scratch our selves

6

what is the first stage of thrombosis?

platelet aggregation

7

describe the process of platelet aggregation

upon coming into contact with collagen, platelets release chemicals (e.g. ADP) from dense granules that cause the aggregation of other platelets, and set off the clotting cascade.

chemicals released from alpha granules cause platelet adhesion to damaged vessel walls.

8

after platelet aggregation, what is next in the process of thrombosis?

platelet aggregation sets off clotting cascade, so a fibrin mesh begins to form - traps red blood cells

9

what tends to initiate arterial thrombosis?

atheromatous plaque protrudes into lumen, causing turbulent blood flow.
turbulence leads to loss of intimal cells.
denuded plaque surface exposed to blood flow - platelets will settle on exposed collagen.
thrombus forms.

10

give an example of what may cause damage to endothelial wall?

cigarette smoking causing endothelial cell injury - change in vessel wall and change in blood flow over injured cells

11

describe the layers seen in an arterial thrombus

first layer = platelet layer - due to platelet aggregation on damaged wall
second layer = fibrin mesh and trapped red blood cells
these alternating layers = lines of Zahn

12

what typically initiates venous thrombosis?

most form at valves - they naturally cause a degree of turbulence - may be damaged by trauma, stasis and occlusion

13

what predisposes someone to venous thrombosis?

fall in blood pressure, causing slowing of blood flow over turbulent areas - eg during surgery, or following MI.
immobility is a big risk for venous thrombosis in calf - stasis, as no contraction of surrounding muscles.

14

define embolism

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

15

list the possible causes of embolus

FATBAT
Fat
Air
Thrombus
Bacteria (endocarditis vegetation)
Amniotic fluid
Tumour

16

describe the path of an embolus in the venous system

vena cava >> through R side of heart >> lodge somewhere in pulmonary arteries.
will not pass through lungs as blood vessels split down to capillary level.

17

describe the path of an embolus in the arterial system

can travel anywhere downstream of its entry point

18

what is the most common cause of a pulmonary embolism?

deep vein thrombosis of the leg becomes dislodged, makes way to pulmonary arterial system and occludes

19

define ischaemia

a reduction in blood flow to a tissue without any other implications

20

define infarction

reduction in blood flow to a tissue to such an extent that it can no longer support maintenance of cells and they die.
"ischaemic death of tissue in living body"

21

what is the most common cause of infarction?

thrombosis of an artery to the extent it occludes it

22

what makes an organ more susceptible to damage by infarction?

end arterial supply - if this supply is interrupted they have no other way of getting nutrients/O2

23

name organs which have a dual arterial supply

liver - portal venous and hepatic artery
lungs - pulmonary venous and bronchial artery
brain - around circle of Willis

24

list some causes infarction/ischaemia

Obstruction:
THROMBOSIS
arterial embolism
atherosclerotic plaques
Compression:
tumour/volvulus/hernia
Vasoconstriction:
e.g. cocaine vasoconstriction --> MI
Rupture of artery due to trauma

25

what are the risk factors for atherosclerosis?

increasing age
male gender
hypertension
smoking
diabetes
hypercholesterolaemia - high LDL, low HDL

26

what is a fatty streak? what is it composed of?

first stage of atheroma formation - yellow elevation of intima.
masses of lipid-laden macrophages.

27

describe the structure of fully developed atherosclerotic plaque

central lipid core
cap of fibrous tissue covered by the arterial endothelium
cap contains macrophages, T lymphocytes and mast cells

28

what provides the structural strength of an atherosclerotic plaque?

connective tissues in the fibrous cap (collagens) - produced by SMCs

29

describe atheromatous lesions

rich in cellular lipids and cellular debris.
soft, semi-fluid, highly thrombogenic lesions.
bordered by a rim of foam cells

30

what are foam cells?

macrophages that have phagocytosed oxidised lipoproteins via a membrane-bound scavenger receptor.
large amounts of cytoplasm, with foamy appearance.