Mechanisms of Atheroma and Infarction Flashcards

1
Q

What is an atheroma?

A

Degeneration of the walls of the arteries.

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2
Q

What is an atheroma caused by and what does it lead to?

A

→ Accumulated fatty deposits and scar tissue

→ Leading to restriction of the circulation and a risk of thrombosis.

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3
Q

What is an infarction?

A

→Obstruction of the blood supply to an organ or region of tissue

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4
Q

What is an infarction typically caused by?

A

→Typically by thrombus or embolus causing local death of tissue.

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5
Q

What is the historical view of atheroma?

A

Young - No fatty deposits
Older - Fat laid down in artery wall
Infarct - Fat stores detach and cause thrombosis.

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6
Q

What is Atherosclerosis ?

A

→A complex inflammatory process

characterized by intimal lesions -atheromas
that impinge on the vascular lumen and can rupture to cause sudden occlusion.
It underlies the pathogenesis of
coronary, cerebral, and peripheral vascular disease

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7
Q

What is Atherosclerosis mediated by?

A

→Mediated by low density lipoprotein (LDL) & Angiotensin II

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8
Q

What makes atherosclerosis worse?

A

→An ongoing systemic inflammatory disease makes it worse (e.g rheumatoid arthritis)

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9
Q

What are common sites for atherosclerosis?

A

→Carotid arteries & circle of Willis
→Coronary arteries
→Iliac arteries
→Aorta

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10
Q

Describe the initiation of plaque formation

A

Inflammatory triggers activate arterial endothelial cells.
→Oxidation of LDL particles stimulated by the presence of necrotic cell debris and free radicals in the endothelium.
→Endothelial cells start to become activated and express cytokines and adhesion molecules.
→Circulating monocytes bind to the activated endothelium.
→They start expressing adhesion molecules and begin to move through the tissue and reside in the intimal layer
→Monocytes differentiate into tissue macrophages which release their own inflammatory mediators.

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11
Q

Describe plaque formation

A

→Macrophages begin to accumulate LDL from the circulation and become foam cells

→Activated foam cells release other growth factors
→This causes smooth muscle cells to leave the medial layer and cross the internal elastic lamina entering the intima.

→The activated smooth muscle cells also release growth factors
→Begin synthesizing collagen and elastin in the intima layer.

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12
Q

Describe the maturation of the plaque

A

Smooth muscle cells accumulate LDL becoming a second type of foam cell
→They continue to make extracellular matrix of elastin and collagen which forms a fibrous plaque.

→ Cells underneath this plaque become oxygen starved and begin to undergo apoptosis.
→They release their fat which forms a globule of fat that is now accumulating in the intima known as the lipid core.

→The dying cells release metalloproteases and other enzymes which can break down the fibrous matrix towards the edge of the plaque
→ Leaving a large lipid core covered by a fibrous plaque that may be vulnerable to enzymatic digestion.

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13
Q

describe how a plaque can rupture

A

If the central core becomes too large, plaque rupture can occur and the sub-endothelium is exposed.
→The endothelium is normally an anticoagulant surface.
→Collagen forms a good base for clotting along with other proteins and factors in the intima.
→This gives a pro-coagulant surface in the artery.
→A thrombus now forms which may occlude the artery.

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14
Q

What is calcification and how is this seen ?

A

→Later on in life calcium deposits may form around the atheroma
→ visible on a CT scan.

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15
Q

What is the role of calcium deposits?

A

→The role of calcium deposits remains uncertain,
→There have been arguments that calcification may actually stabilise the plaque.
→Calcium may be a bad thing but paradoxically a lot of calcium deposits rather than a few may be advantageous.

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16
Q

When was atheroma first found?

A

→Mummified remains suggest that atheroma is as old as modern man
→found in hunter-gatherer societies.

17
Q

What % of people have smooth muscle foam cells by puberty?

A

→65% of people have smooth muscle foam cells by puberty.

18
Q

When does maturation of the fibrous cap occur? (what age)

A

→30-40 years old

19
Q

When do macrophage foam cells develop?

A

→Macrophage foam cells develop between birth and 10 years of age.

20
Q

what is occlusive thrombosis and what is an example of it?

A

e.g Myocardial Infarction

→Occurs when blood flow decreases or stops to part of the heart causing damage to the heart muscle.

21
Q

What is a thromboembolism and what is an example of it?

A

→eg. Ischaemic Stroke
→Obstruction due to an embolus from elsewhere in the body (usually carotid artery) blocking blood supply to part of the brain.

22
Q

What is an example of an aneurysm due to wall weakness?

A

eg. Aortic Aneurysm
→Cause weakness in the wall of aorta and increases the risk of aortic rupture.

→When rupture occurs, massive internal bleeding results and unless treated immediately shock and death can occur.

23
Q

What are 5 factors that can cause atheroma?

A

→Systemic inflammation promotes atheroma formation
→Smoking
→Parasite infections lead to chronic inflammations
→Genetics
→Lifestyle choices

24
Q

Where does arterial occlusion occur?

A

→Particulary cardiac and carotid arteries.

25
Q

What is arterial occlusion?

A

→Anything downstream from arterial occlusion becomes starved of oxygen.

26
Q

What can arterial occlusion lead to?

A

→reduced blood flow can lead to symptoms of angina on exercise.

27
Q

What can a detached thrombus cause?

A

→Can block the cardiac arteries (MI) or cerebral arteries (stroke) and cause death or serious damage quickly.

28
Q

What are the symptoms of venous occlusion and

What can the thrombus then do?

A

→Occlusion does not cut off the blood supply.
→Causes pain and swelling as hydraulic pressure causes oedema.
→Thrombus may detach and return to the right side of the heart and could enter the pulmonary circulation
→Causing a pulmonary embolism.

29
Q

What is stable cardiac angina due to?

A

→Due to permanent flow limitation.
→Coronary artery is no longer capable of dilating and allowing more blood flow.
→Not necessarily infarction.

30
Q

What is a symptom of stable cardiac angina?

A

→Chest pain when engaging in physical activity.

31
Q

What is unstable cardiac angina due to?

A

→transient thrombosis.

→Not necessarily infarction.

32
Q

What is a symptom of unstable cardiac angina?

A

→chest pain occurs without physical activity.

33
Q

What is Myocardial infarction due to and what happens to muscle tissue?

A

→Due to complete occlusion.

→Muscle tissue downstream begins to die.

34
Q

What does STEMI stand for?

A

→ST Elevated Myocardial Infarction

35
Q

Why is the ST section elevated?

A

Damaged heart tissue does not depolarise properly so this section is elevated above the baseline.

36
Q

how does a stroke due to thromboembolism happen?

A

Thrombus at carotid plaque rupture travels to smaller cerebral vessels.

37
Q

How does a non-thromboembolic stroke happen and what happens?

A

and what happens?

Due to hypo-perfusion
Loss of blood pressure (e.g heart failure, haemorrhage, shock) or aneurysm rupture and bleeding in the brain.