Vessels

Question 1

Describe phenotypic heterogeneity

Answer 1

Arteries- ECs aligned in direction of flow, long and narrow cells, continuous endothelium with many tight junctions, no valves, specific markers- Ephrin B2
Veins- continuous endothelium, shorter wider cells not aligned in direction of flow, have valves, specific markers- Ephrin B4

Question 2

Summarise endothelial function

Answer 2

Regulates vascular homeostasis
Acts as both sensor and effector
-blood flow regulation
-permeability
-homeostasis 
-neutrophil/leukocyte recruitment
-hormone trafficking

Question 3

Describe endothelial barrier function

Answer 3

Continuous non-fenestrated endothelium found in arteries, veins and capillaries if the brain, skin and heart- paracellular transport of water and small solutes, transcytosis- caveole smooth membrane invaginations and vesicles
Fenestrated continuous found in the glomerulus- pores have a diaphragm- permits greater transendothelial transport of fluids and solutes
Sinusoid found in the liver- large fenestrations that lack a diaphragm with a poorly formed basement membrane- high endocytic activity in clathrin-coated pots
Contain tight junctions (claudins, occludins, junctional adhesion molecules- JAMs)
Adherens- VE-cadherin
Gap junctions- connexins

Question 4

What are VVOs?

Answer 4

Vesicular-vacuolar organelles
Form transcellular channels when they connect
A major route for transport of fluids and solutes across the endothelium particularly inflammatory situations

Question 5

How does the endothelium provide a non-thrombogenic surface?

Answer 5

Tissue factor pathway inhibitor- blocks activation of extrinsic pathway
Thrombomodulin
Endothelial protein C receptor (EPCR)
Tissue-type plasminogen activator (t-PA)
Prostacyclin and NO
Tissue plasminogen activator
ATPase breaks ATP down into AMP so it cannot activate platelets

Question 6

What is the procoagulant by activity of the endothelium?

Answer 6

Induction of tissue factors
Plasminogen activator inhibitor-1
von Willebrand factor release

Question 7

Describe the maturation if blood vessels

Answer 7

1. Endothelial cell tube
2. Capillary- EC tube, pericyte, basement membrane
3. Arterioles and venules- EC tube, internal elastic lamina, smooth muscle cell, basement membrane, external elastic lamina
4. Lymphatics- endothelial cells and valves, initial lymphatic and collecting lymphatics

Question 8

Describe vascular endothelial growth factor

Answer 8

VEGF is the master regulator of physiological and pathological cal angiogenesis
Selective for endothelial cells via three high-affinity receptors
Loss of one allele is embryonic lethal
Over-expression leads to severe abnormalities and death in utero
In the adult VEGF overexpression leads to oedema and tumour growth
Inhibition cause hypertension, proteinuria, bleeding gums

Question 9

Summarise the regulation of vascular tone

Answer 9

Vasodilation- NO and prostacyclin

Vasoconstriction- endothelin1, thromboxane, hydrogen peroxide, superoxide anion

Question 10

Describe NO synthesis pathway

Answer 10

L-arginine converted by coupled eNOS to make NO and L-citruline
Or L-arginine is used in protein synthesis and the degraded in to ADMA and excreted
eNOS- regulation of vascular tone, inhibition of smooth muscle cell proliferation, inhibition of platelet aggregation

Question 11

Describe the regulators of eNOS activity

Answer 11

Phosphorylation
Association with co-factors- BH4
Cellular location- sequestration by calveolin1 in a less active state
Calmodulin binds with calcium after its release from calveolin, hsp90 binds, Akt and PKA phosphorylate it

Question 12

Describe the activity of NO

Answer 12

Freely diffusible gas that acts as a signalling molecule
Local activity- short half-life
Activity limited by circulating haemoglobin
Prevents thrombosis
Anti-inflammation
Anti-oxidant
Inhibits smooth muscle proliferation and migration
Atheroprotective
Activates guanylate cyclase- produces cGMP reduces Ca2+ and activates phosphodiesterase, activates PKG which limits activation if the myosin light chain and therefore cross-bridging

Question 13

What is the function of prostacyclin on vascular smooth nuclear relaxation?

Answer 13

Bind IP receptors
Activates adenylate cyclase
Increasing cAMP conc activates PKA
Decreases Ca conc limiting smooth muscle contraction

Question 14

What can be a consequence of eNOS uncoupling?

Answer 14

Loss of BH4 uncoupled the eNOS dimer- decreases NO and promotes superoxide generation
Increased NADPH and xanthine oxidase activity increase superoxide production
Peroxynitrite (OONO-) leads to further uncoupling of eNOS after oxidative damage to eNOS and/or BH4

Question 15

Describe vascular complication in diabetes mellitus

Answer 15

Central and peripheral vasculopathies- retinopathy, neuropathy, nephropathy
Increased risk of cardiovascular disease due to plaque rupture find atherothrombosis
Excessive O2- generation in mitochondria intimidates the vascular injury in response to hyperglycaemia

Question 16

What is pre-eclampsia?

Answer 16

Maternal systemic syndrome caused by abnormal placentation in the first trimester
30% associated with intrauterine growth restriction of the foetus
Only cure is the delivery of the placenta
Leads to systemic endothelial activation, systemic inflammatory response
Splice variants of the flt1 gene are produced by the placenta and act to sequester VEGF and antagonise its activity in the maternal circulation

Question 17

What nerves supply blood vessels?

Answer 17

Most vessels have only sympathetic innervation perivascular verve fibres in the adventia-media border and do not penetrate into the VSM
Vasoconstrictor- NA, ATP, NPY
Dilator- ACh, VIP and NO
Except from the cerebrum, heart, and reproductive tissue which also have parasympathetic
ACh, VIP NO

Question 18

Describe varicosities

Answer 18

Granular vesicles contain NA ATP
Large opaque vesicles contain NYP
Release is as the action potential passes
NA production is matched to nerve activity
Increase nerve activity leads to increased enzymatic activity in the conversion of tyrosine to DOPA to dopamine to NA
There is also re-uptake via a NA transporter
After release they act on alpha1 and alpha2 receptors on the vessel and diffuse into the blood stream or broken down by COMT, act on pre-synaptic alpha2 inhibition receptors, re-uptake, break down by MAO

Question 19

Describe the differential distribution of adrenoceptors

Answer 19

There are fewer alpha1 receptor in vessels as you approach the distal arterioles
Their constrictor influence is more easily blunted by local dilator influences

Question 20

List some agonist as and antagonist to alpha receptors

Answer 20

A1 agonist- phenylephrine
Antagonist- prazosin
A2 agonist- clonidine
Antagonist- yohimbine
Non selective agonist- phenylephrine

Question 21

Describe the effects of NA on VSM via A1 and A2 receptors

Answer 21

A1- stimulates PLC to convert PI to insP3 which acts triggers the release of more Ca from the sarcoplasmic reticulum
Stimulates voltage gated Ca channels leads to influx of Ca
A2- activation leads to the inhibition of K channels leading to depolarisation and activation of voltage gated Ca channels leading to an influx of calcium
Increased intracellular calcium leads to contraction

Question 22

Describe the release and action of co-transmitter ATP

Answer 22

Purinergic receptors- P1- adenosine
P2- ATP ADP AMP
(P2X-1 on VSM and P2Y I. The endothelium)
ATP is metabolised by ecto-nucleotidases to AMP and then to adenosine by 5’ nucleotidases
Adenosine acts on pre-synaptic P1 receptors inhibiting ATP release
ATP primes the VSM for the action of NA

Question 23

Describe neuropeptide Y

Answer 23

Discharged with long periods of high frequency activity
Produces slow and long-lasting constriction, particularly in the presence of NA
Y1 main receptor in VSM
Y2 pre-junctional, modulates NPY/ATP/NA release
Terminated by peptidases
Facilitated vasoconstriction evoked by ATP and NA
Released in order to prevent a catastrophic fall in ABP in the case of haemorrhage, dehydration, shock and heart failure

Question 24

Describe the synthesis and release of ACh VIP and NO

Answer 24

Choline Acetyltransferase makes ACh
nNOS synthesises NO
Vesicle containing ACh and VIP act on VIP receptor on the smooth muscle
And on the muscarinic receptor on the endothelium to synthesis and release NO
NO acts on the smooth muscle
ACh is degraded by acetylcholine esterase and the choline is recycled

Question 25

Describe the possible effects of nerve released ACh VIP and NO on VSM

Answer 25

NO acts on Guanine cyclase to produce cGMP which causes dilation VIP actor to stimulate K channels to hyperpolarise cells and inhibit the activation of voltage gated Ca channels

Question 26

List the influences on blood vessels in vivo

Answer 26

``` Myogenic tone (ABP) Sympathetic noradrenergic Endothelium derived substances Hormones, O2, CO2 etc in blood Substances released from tissue cells that accumulate in the interstitial space ```

Question 27

Describe the hormonal influences on blood vessels

Answer 27

Catecholamines- adrenaline, noradrenaline- released from the adrenal medulla in response to environmental stressors, strenuous exercise, cold etc NA- weak of all arterioles except cerebral- stimulates alpha2 receptors➡️ NO Adrenaline- vasodilation in skeletal muscle only- beta2 receptors occur on VSM and endothelial cells- stimulates NO synthesis and increasing cAMP -vasoconstriction in all other vessels (alpha receptors) ADH- released by pituitary gland- acts on V1 receptors on VSM- vasoconstriction Angiotensin2- acts in AT1 receptors on VSM- vasoconstriction

Question 28

Summarise local influences on blood vessels

Answer 28

Blood flow is regulated by local mechanisms to support tissue metabolism- 'flow-metabolism coupling' Little variation in skin and kidney Can vary a lot in skeletal muscle, cardiac muscle and brain

Question 29

Describe the response to system hypoxia

Answer 29

Fall in PaO2 affects endothelial cells- Release adenosine➡️ stimulates NOS and COX Fall in PaO2 affects RBCs- release ATP when O2 is offloaded via pannexin channels ATP produces vasodilation via P2Y receptors on endothelial cells ATP metabolised by ecto-nucleotidases to ADP, AMP and adenosine which acts on endothelial P1 receptors Vasodilation increases blood flow and shear stress which further stimulates NO Fall in PaO2 also inhibits vasoconstrictors

Question 30

Describe the response to muscle hypoxia

Answer 30

Muscle contraction causes 1. K efflux- vasodilator 2. ATP release- metabolised by ectonucleotidases to adenosine 3. ATP degradation also produces inorganic phosphate 4. Synthesis and release of PGE2 Dilation caused by K induced hyperpolarisation which closes Voltage gated Ca channels on VSM Adenosine acting in VSM P1 receptors PGE2 acting in EP receptors RBC release O2 and ATP which may induce dilation via endothelial P2Y receptors Vasodilation increases shear stress which stimulates NO production

Question 31

Summarise the Berne hypothesis

Answer 31

Adenosine is manly responsible for matching O2 delivery to VO2 in cardiac muscle and coronary blood flow Produced by endonucleotidases from AMP

Question 32

Summarise cerebral circulation

Answer 32

Increased neuronal activity requires more O2 and glucose mostly by increasing delivery by vasodilation which has to be compensated by vasoconstriction elsewhere to prevent increased intracranial pressure Responses to changes in local CO2 are thought to occur by stimulation of prostaglandin synthesis Responses to local O2 occur via adenosine, prostaglandins and NO via the endothelium

Question 33

Summarise glial cell function with cerebral blood flow

Answer 33

Interneurones release glutamate Glial cells siphon up K and release near arterioles which cause the hyperpolarisation of VSM Glial cells also synthesise and release prostaglandins and adenosine

Question 34

What is the difference between angiogenesis and vasculogenesis?

Answer 34

Angiogenesis is the formation of blood vessels from other blood vessels, vasculogenesis is the formation of new blood vessels from mesodermal derived angioblasts

Question 35

List the roles of angiogenesis

Answer 35

During development Physiological processes- wound healing, menstruated cycle, adaption to increased muscle activity Pathological processes- cancer, inflammatory, diabetic retinopathy

Question 36

Describe the process of vasculogenesis

Answer 36

``` Endothelial progenitors (angioblasts) differentiate from mesodermal cells Angioblasts coalesce to form first embryonic vessels- dorsal aorta and cardinal vein Angioblasts from blood islands which fuse and remodel to form a primitive capillary plexus ```

Question 37

Describe angiogenesis during development

Answer 37

Angiogenic remodelling of dorsal aorta, cardinal vein and vascular plexi give rise to arteries, veins and capillaries Pericyte a are recruited to stabilise capillaries Lymphatic endothelial cells sprout from veins and form they lymphatic system via lymphangiogenesis

Question 38

What is the main cause of physiological angiogenesis?

Answer 38

Hypoxia- Hypoxia Inducible Factor (HIF)-1 is a transcription factor and a master regulator of oxygen homeostasis Consists of alpha and beta subunits Degradation of HIF-1alpha is regulated in response oxygen levels In high levels proline hydroxylase hydroxylases proline residues on the alpha subunit so it is then recognised and bind by ubiquitin ligase which polyubiquitates it to be degraded If there isn't enough oxygen to drive the proline hydroxylation the alpha subunit associates with the beta subunit and activates its target genes eg. VEGF

Question 39

What is the function of VEGF in endothelial cells?

Answer 39

VEGF-A is the potent driver of angiogenesis VEGFR signals via activation of VEGFR-2 a receptor tyrosine kinase Dimerisation of VEGFR-2 activates signalling pathways which affects- proliferation, survival, migration, vascular permeability

Question 40

Summarise the modes of angiogenesis

Answer 40

Sprouting or splitting (intussusception) Induced by shear stress- Intussusception involved the formation of a pillar which elongates splitting the vessel in two- rapid increase in capillarity and requires minimal endothelial proliferation Tissue stretch- Sprouting involves the formation of a new capillary off another

Question 41

Describe the stages of sprouting

Answer 41

VEGF regulated VE-cadherin and loosens endothelial junctions Endothelial cells secrete proteases to remodel existing interstitial matrix Selection of tip cell to guide the newly forming sprout- filopodia sense the extracellular environment and secrete VEGF Pericyte detachment mediated by Angiopoeitin Increased permeability allows the deposition of plasma proteins to make a provisional matrix Notch signalling between the tip (delta-like 4) and stalk cells (notch) maintains their different specification Stalk cells behind the top proliferate and extend the sprout- VEGFR-2 is down regulated Stalk attracts pedicures to stabilise the newly formed vessels Tip cells navigate in response to guidance signals and adhere to the extracellular matrix (mediated by integrins) to migrate Sprouts from adjacent vessels grow towards each other Formation of tight junctions, basement membrane deposition, pericytes maturation Angiopoeitin signalling between endothelial cells and pericytes maintain quiescence of the vessel

Question 42

Summarise pathological angiogenesis

Answer 42

Tumour growth and hyperplasia in inflammatory diseases increase the distance of cells from vessels and chronic hypoxia drives VEGF production plus inflammatory cytokines gives rise to a pro-angiogenic environment Vessel formation is abnormal leading to leaky and poorly perfused vessels and persistent hypoxia

Question 43

How would you modulate angiogenesis via VEGF?

Answer 43

Inhibit signalling using a monoclonal antibody eg. Bevacizumab, used in cancer s d diabetic retinopathy Use a soluble receptor- VEGF trap Small molecule inhibitors eg. Sunitinib, sorafenib used in cancer treatment Antibody blocking binding if VEGF to the receptor eg. IMC 1C11