Vascular Endothelium

Question 1

Where do most endothelial cells reside?

Answer 1

In the microvasculature

Question 2

Name the 3 layers of blood vessels from innermost to outermost

Answer 2

Tunica intima
Tunica media
Tunica adventitia

Question 3

What is the tunica intima made of?

Answer 3

Endothelium

Question 4

What is the tunica media made of?

Answer 4

Smooth muscle cells

Question 5

What does the tunica adventitia contain?

Answer 5

Vasa vasorum

Question 6

Do all blood vessels have 3 layers?

Answer 6

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

Question 7

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

Answer 7

Mural cells aka pericytes

Question 8

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

Answer 8

Angiocrine factors

Question 9

What are angiocrine factors?

Answer 9

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

Question 10

How thick are endothelial cells?

Answer 10

1-2 micrometres

Question 11

What is the diameter of an normal endothelial cell?

Answer 11

10-20 micrometers

Question 12

What is contact inhibition?

Answer 12

When 2 endothelial cells come together and stop growing

Question 13

How often do endothelial cells proliferate?

Answer 13

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

Question 14

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

Answer 14

Tissue homeostasis and regeneration
Permeability
Vascular tone
Inflammation
Angiogenesis 
Haemostasis and thrombosis

Question 15

What type of cell are endothelial cells?

Answer 15

Heterogeneous

Question 16

Why is dysfunction of the endothelium so significant?

Answer 16

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

Question 17

What is tissue specific microvasculature?

Answer 17

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

Question 18

What are the characteristics of resting endothelium?

Answer 18

Anti inflammatory
Anti thrombotic
Anti proliferative

Question 19

What are the characteristics of activated endothelium?

Answer 19

Pro inflammatory
Pro thrombotic
Pro angiogenic

Question 20

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

Answer 20

It must be chronically activated

Question 21

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

Answer 21

Dysfunction allowing leukocyte migration and adhesion

Formation of a fatty streak due to foam cell activation

Question 22

Name some stimuli and risk factors for endothelial cell dysfunction

Answer 22

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

Question 23

What is the leukocyte cascade?

Answer 23

The process by which leukocytes migrate into tissues

Question 24

What is the leukocyte cascade usually important for?

Answer 24

Fighting inflammation

Question 25

Describe the process of the leukocyte cascade

Answer 25

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

Question 26

What type of blood vessel do leukocytes usually adhere to?

Answer 26

The endothelium of post capillary venules

Question 27

In atherosclerosis what do leukocytes adhere to?

Answer 27

The endothelium of large arteries

Question 28

Describe how a fatty streak forms in atherosclerosis

Answer 28

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

Question 29

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

Answer 29

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

Question 30

How long does the development of atherosclerosis take?

Answer 30

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

Question 31

Where do atherosclerotic plaques form preferentially?

Answer 31

In curvatures or bifurcations of vessels

Question 32

Why do atherosclerotic plaques form in specific places preferentially?

Answer 32

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

Question 33

Describe blood flow and sheer stress in straight parts of arteries

Answer 33

There is laminar flow | Sheer stress is high and directional

Question 34

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

Answer 34

Flow is disturbed | Sheer stress is low

Question 35

What does laminar flow promote

Answer 35

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

Question 36

What does disturbed flow promote

Answer 36

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

Question 37

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

Answer 37

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)

Question 38

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

Answer 38

Reduced production

Question 39

Define angiogenesis

Answer 39

The formation of new blood vessels via sprouting from existing vessles

Question 40

What is the main trigger for angiogenesis

Answer 40

Hypoxia

Question 41

What is the Janus paradox?

Answer 41

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

Question 42

What happens to the endothelium in covid?

Answer 42

There is loss of endothelial homeostasis via systemic endothelial oxidation

Question 43

What cells are a sign of endothelial damage?

Answer 43

Circulating endothelial cells

Question 44

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

Answer 44

A cytokine storm thats secondary to covid | Covid entering endothelial cells and causing direct damage

Question 45

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

Answer 45

Thromboinflammation