Vascular Endothelium Flashcards

1
Q

Where do most endothelial cells reside?

A

In the microvasculature

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2
Q

Name the 3 layers of blood vessels from innermost to outermost

A

Tunica intima
Tunica media
Tunica adventitia

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3
Q

What is the tunica intima made of?

A

Endothelium

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4
Q

What is the tunica media made of?

A

Smooth muscle cells

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5
Q

What does the tunica adventitia contain?

A

Vasa vasorum

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6
Q

Do all blood vessels have 3 layers?

A

No capillaries and venules don’t, they have one layer of endothelium

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7
Q

What supportive cells are present in the basement membrane of capillaries and venules?

A

Mural cells aka pericytes

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8
Q

What are the factors produced by blood vessels that are needed to maintain tissue homeostasis called?

A

Angiocrine factors

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9
Q

What are angiocrine factors?

A

Factors produced by blood vessels that are needed to maintain tissue homeostasis

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10
Q

How thick are endothelial cells?

A

1-2 micrometres

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11
Q

What is the diameter of an normal endothelial cell?

A

10-20 micrometers

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12
Q

What is contact inhibition?

A

When 2 endothelial cells come together and stop growing

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13
Q

How often do endothelial cells proliferate?

A

Very rarely, they have a long lifespan and will only proliferate when new blood vessels are required

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14
Q

What are some functions controlled by the endothelium of blood vessels?

A
Tissue homeostasis and regeneration
Permeability
Vascular tone
Inflammation
Angiogenesis 
Haemostasis and thrombosis
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15
Q

What type of cell are endothelial cells?

A

Heterogeneous

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16
Q

Why is dysfunction of the endothelium so significant?

A

It contributes to disease more than any other organ, this includes ischaemia, cancer, diabetes etc

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17
Q

What is tissue specific microvasculature?

A

The idea that not all blood vessels are the same and have adaptations depending on which tissue they supply

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18
Q

What are the characteristics of resting endothelium?

A

Anti inflammatory
Anti thrombotic
Anti proliferative

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19
Q

What are the characteristics of activated endothelium?

A

Pro inflammatory
Pro thrombotic
Pro angiogenic

20
Q

What state must the endothelium be in for atherosclerosis to develop?

A

It must be chronically activated

21
Q

What are the 2 main steps in the development of atherosclerosis?

A

Dysfunction allowing leukocyte migration and adhesion

Formation of a fatty streak due to foam cell activation

22
Q

Name some stimuli and risk factors for endothelial cell dysfunction

A
Hypercholesterolaemia
Diabetes mellitus
Hypertension
Sex hormone imbalance
Ageing 
Oxidative stress
Proinflammatory cytokines 
Infectious agents
Environmental toxins
Haemodynamic forces
23
Q

What is the leukocyte cascade?

A

The process by which leukocytes migrate into tissues

24
Q

What is the leukocyte cascade usually important for?

A

Fighting inflammation

25
Q

Describe the process of the leukocyte cascade

A
Capture
Rolling (during which activation occurs)
Arrest
Adhesion, strengthening and spreading
Paracellular and transcellular migration
26
Q

What type of blood vessel do leukocytes usually adhere to?

A

The endothelium of post capillary venules

27
Q

In atherosclerosis what do leukocytes adhere to?

A

The endothelium of large arteries

28
Q

Describe how a fatty streak forms in atherosclerosis

A

Leukocytes adhere to the endothelium of blood vessels
They attempt to migrate into the blood vessel but get stuck in the subendothelial space
Monocytes differentiate into macrophages here and become foam cells

29
Q

Describe how changes in the permeability of blood vessels affects formation of fatty streaks

A

As vessels become more permeable, lipoproteins can easily leak through the junctions into the subendothelial space
Here the lipoproteins are oxidised and combine with macrophages to form foam cells

30
Q

How long does the development of atherosclerosis take?

A

A long time, the formation of foam cells is not a quick process

31
Q

Where do atherosclerotic plaques form preferentially?

A

In curvatures or bifurcations of vessels

32
Q

Why do atherosclerotic plaques form in specific places preferentially?

A

Flow patterns and haemodynamic forces are not uniform in the vascular system

33
Q

Describe blood flow and sheer stress in straight parts of arteries

A

There is laminar flow

Sheer stress is high and directional

34
Q

Describe blood flow and sheer stress in the branches and curvatures of arteries

A

Flow is disturbed

Sheer stress is low

35
Q

What does laminar flow promote

A

Anti thrombotic and anti inflammatory factors
Endothelial survival
Inhibition of SMC proliferation
Nitric oxide production

36
Q

What does disturbed flow promote

A

Thrombosis, inflammation (leukocyte adhesion)
Endothelial apoptosis
SMC proliferation
Loss of nitric oxide production

37
Q

What is the significance of nitric oxide in relation to the cardiovascular system?

A

It is a key regulator of the system, it:
dilates blood vessels
Reduces platelet stickiness
Reduces oxidation of LDL cholesterol (a major component of plaque)
Reduces release of superoxide radicals
reduces multiplication of smooth muscle cells of the artery wall
Reduces monocyte stickiness (prevents the formation of plaque)

38
Q

What happens to nitric oxide production that encourages development of atherosclerosis?

A

Reduced production

39
Q

Define angiogenesis

A

The formation of new blood vessels via sprouting from existing vessles

40
Q

What is the main trigger for angiogenesis

A

Hypoxia

41
Q

What is the Janus paradox?

A

The idea that angiogenesis can be both good and bad:
It is bad as it promotes plaque growth
It is good as therapeutic angiogenesis prevents damage post ischemia

42
Q

What happens to the endothelium in covid?

A

There is loss of endothelial homeostasis via systemic endothelial oxidation

43
Q

What cells are a sign of endothelial damage?

A

Circulating endothelial cells

44
Q

What are the 2 possible mechanisms of to the endothelium in covid?

A

A cytokine storm thats secondary to covid

Covid entering endothelial cells and causing direct damage

45
Q

What process occurs in covid due to loss of normal endothelium?

A

Thromboinflammation