Vascular Endothelium Flashcards
What are the three main layers of the vascular endothelium?
Tunica adventitia
Tunica media
Tunia intima
What is found within the tunica adventitia?
Vaso vasorum
Nerves
Which types of fibres form the tunica media?
Smooth muscle cells and elastic fibres
What is the tunica intima?
Endothelium
Which cells support the venule and capillary endothelium?
Mural cells (pericytes)
What is the function of pericyte?
Maintains homeostatic and haemostatic function
What are the main functions of the microvascular endothelium? (6)
- Release angiocrine factors
- Regulate permeability of vessels
- Regulate immune response
- Angiogenesis
- Vascular tone
- Haemostasis and thrombosis
Which factor is secreted by the endothelium and mediates platelet adhesion?
Von Willebrand Factor
What is endothelial heterogeneity?
Endothelial cells and microvasculature have organotypic (tissue specific) properties and expression profiles.
The endothelial phenotype is dependent on location
What are the three types of endothelium?
Fenestrated continuous endothelium
Non-fenestrated continuous endothelium
Discontinuous
Where are fenestrated continuous endothelium found?
Kidney glomerulus, and gastrointestinal tract to facilitate filtration and absorption
Where are the non-fenestrated continuous endothelium found?
In muscle and blood brain barrier
What type of endothelium forms the blood brain barrier?
Non-fenestrated
What type of endothelium is found within the liver?
Discontinuous
What type of layer is formed by the endothelium?
Monolayer
Which types of proteins are involved in cell adhesion and the formation of the monolayer?
E-cadherins
Which process arrests cell growth when cells come in contact with each other?
Contact inhibition
Describe the proliferation rate in endothelial cells
Low proliferation rate unless angiogenesis is induced
What is the resting equilibrium in endothelial cells?
A balance between anti-inflammatory, anti-thrombotic and anti-proliferative factors with
pro-inflammatory, pro-thrombotic and pro-angiogenic factors
Which factors activate the endothelium?
OxLDL, High glucose, High blood pressure, Inflammation, Mechanical stress, Viruses, Smoking
What are the responses of the activated endothelium?
Thrombosis
Senescence
Permeability
Leukocyte recruitment
What are the matrix products involved in angiogenesis?
Fibronectin Laminin Collagen Proteoglycans Proteases
What are the growth factors concerned with angiogenesis?
Insulin-like growth factor
Transforming growth factor
Colony stimulating factor
Which adhesion molecules exist on the endothelium and promote neutrophil migration?
ICAM and VCAM
Selectins - P-selectin
Which inflammatory mediators are secreted by the endothelium?
IL-1, 6, 8
Leukotrienes
MHC-II
What are the four main functions of the endothelium?
Angiogenesis
Inflammation
Vascular tone and permeability
Thrombosis and haemostasis
Which type of factor is endothelin?
Vasoconstricting factor
Which type of factor is thromboxane A2?
Vasoconstricting factor
What are the vasoconstricting factors released by the endothelium?
Angiotensin-Converting Enzymes (ACE) Thromboxane A2 Leukotrienes Free radicals Endothelin
What are the two vasodilator factors released by the endothelium?
Nitric oxide
Prostacyclin
What are the procoagulant factors that are released by the endothelium?
- Von Willebrand factor
- Thromboxane A2
- Thromboplastin
- Factor V
- Platelet activating factor
- Plasminogen activator inhibitor
What are the anti-thrombotic factors released by the endothelium?
• Prostacyclin,
thrombomodulin, antithrombin, PA heparin.
What is the first step of the pathogenesis of atherosclerosis?
Increased endothelial permeability to lipoproteins and plasma constituents mediated by nitric oxide, prostacyclin, platelet derived growth factor and endothelin.
Which molecules are upregulated by leukocytes that promote adhesion to the endothelium?
Leukocyte adhesion molecules:
L-selectin
Intregrins and platelet endothelial cell adhesion molecule
Which molecules are upregulated by endothelial cells that promote leukocyte adhesion
Endothelial adhesion molecules E and P-selectin
Which molecules promote the migration of leukocytes into the artery wall?
Mediated by low-density lipoprotein MCP-I IL-8 Osteopontin M-CSF
Which molecules are released by macrophages which oxidise LDLs?
Free oxygen radicals
The phagocytosis of OxLDLs by macrophages forms what type of cell?
Foam cell
Fatty streak accumulation within the tunica media induces a fibrotic repair process forming what?
A fibrous cap
What is ultimately formed due to foam cell formation within the tunica media?
A necrotic core formed from leukocytes , lipids and debris
Which factors promote macrophage migration into the sub-endothelium?
MCP-I, MCSF and oxidised low density lipoprotein
What does the necrotic core represent?
Represents the results of apoptosis and necrosis, increased proteolytic activity and lipid accumulation
What factors contribute towards endothelial cell dysfunction?
Hyperchoelsterolemia
Diabetes mellitus/metabolic syndrome
Hypertension
sex-hormonal imbalance
Ageing
Oxidative stress
Pro-inflammatory cytokines
infectious agents
Environmental toxins
haemodynamic forces
What are the four stages of the pathogenesis of atherosclerosis?
- Leukocyte recruitment
- Permeability
- Shear stress
- Angiogenesis
Which chemokine promotes neutrophil migration?
IL-8
Which inflammatory cell releases IL-8?
Macrophage
What are the functions of IL-8?
Chemoattractant of neutrophils
Upregulates endothelial adhesion molecules (selectins)
What are the first stages of neutrophil migration?
Rolling and adhesion occurs as neutrophils establish reversible binding between selectins on the endothelial surface and carbohydrate ligands.
Which tight adhesive molecules are found on neutrophils and interact with the endothelium?
MAC-I
LFA-I
Which tight adhesive molecules are found on the endothelium to interact with migrating neutrophils?
ICAM-I and 2 ligands
What is diapedesis?
The movement of neutrophils from the circulation into the tissues
Which molecules foster transcellular interactions for neutrophils?
PECAM and JAM interactions
Where does the majority of leukocyte transmigration occur?
Post-capillary venules
What surrounds the capillary?
Basement membrane and pericapillary cells (pericytes)
Which CD marker is produced by endothelial cells and contribute to diapedesis?
CD99
What is the function of CD99?
Upregulates laminin binding integrin
How do neutrophils transmigrate into tissues?
- Infiltrating neutrophils disrupt the interaction of junctional adhesion molecules (JAM) and vascular endothelial cadherins.
- Neutrophils display motility involving membrane protrusions and the rearrangement of the cytoskeleton of pseudopodia - Mediated by PECAM interactions on both cells.
Where do leukocytes transmigrate into?
Tunica intima and subendothelial space
What is found in the subendothelial space?
Extracellular matrix of proteoglycans and lipids
What is the effect of increasing endothelial permeability and atherosclerosis?
Lipoproteins pass through the fenestrations into the subendothelial space.
Macrophages transmigrate into the subendothelial space, detecting LDLs via scavenger receptors
Which type of macrophage receptors detect lipoproteins?
Scavenger receptors
What forms foam cells?
Oxidised lipoproteins within macrophages
Which areas potentiate atheroma formation?
Curvatures and bifurcations (Ascending aorta and the aortic bifurcation of the abdominal aorta) results in non-uniform haemodynamic forces, potentiating the probability of atheroma formation
How do plaques affect shear stress?
Narrows the arterial lumen disrupting the laminar flow, thus blood flows in a turbulent manner reducing shear stress that is exerted onto the vascular endothelial cells -disturbing the homeostatic balance that ultimately leads to thrombosis and inflammation
What is laminar flow?
Blood flows in discrete current lines with minimal interference with each other
What are the three characteristics of laminar flow?
- Velocity is constant at any one point, flowing in layers.
- Blood flows fastest at the centre of flow.
- Wall shear stress exerted on the endothelium is high and directional.
When is shear stress high on the endothelium?
During laminar flow
What happens to shear stress during turbulent flow?
In branches and curvatures, blood flow is distributed with nonuniform and irregular distribution of low wall shear stress.
What does laminar flow promote?
factors
• Endothelial survival
• Inhibition of Smooth Muscle Cell proliferation
• Nitric oxide (NO) production (Vasodilator)
What happens to nitric oxide production in turbulent flow?
Decreases NO production
What happens to smooth muscles in turbulent flow?
Smooth muscle cell proliferation
What type of environment is maintained by laminar flow?
High shear stress exerted onto the endothelium by laminar flows maintains an antithrombotic and anti-inflammatory environment.
What happens during turbulent flow?
- Thrombosis, inflammation (leukocyte adhesion)
- Endothelial apoptosis
- Smooth Muscle Cell proliferation
- Loss of Nitric oxide (NO) production
What is the function of nitric oxide released by endothelial cells on lipoproteins?
NO reduces the oxidation of LDL cholesterol (major component of plaque)
What effect is exerted by NO on platelets?
Anti-thrombotic, reduces platelet activation.
What effect does NO have on the vessels?
Dilation of blood vessels
What effect does NO have on superoxides?
NO reduces the release of superoxide radicals from macrophages and neutrophils
What are the 6 main functions of nitric oxide?
- Reduces platelet activation Anti-thrombotic
- Reduces release of superoxide radicals from macrophages and neutrophils.
- Dilates blood vessels
- Reduces proliferation of smooth muscle cell within the tunica media
- Inhibits monocyte adhesion
Which factor stimulates angiogenesis in hypoxic conditions?
Hypoxia inducible factor stimualtes epo production and potentiates activity of angiogenesis.
What are the benefits of angiogenesis?
Embryonic development, menstural cycle and wound healing
What is the janus paradox?
Angiogenesis within the vaso vasorum of the adventitia promotes plaque formation
Revascularisation uses the principle of angiogenesis for therapeutic treatment of post-ischaemic coronary arteries.
What is the therapeutic treatment of post-ischaemic coronary arteries?
Revascularisation
What is a marker of endothelial injury?
Circulating endothelial cells