Heart failure - Endothelial regulation of vascular tone

13 important questions on Heart failure - Endothelial regulation of vascular tone

What is the function and structure of the aorta and large arteries?

pulse dampening & distribution blood
high pressure: "pressure reservoir"
thick-walled, muscular & elastic

-> conducting vessels

What is the function and structure of the small arteries and arterioles?

supply capillary beds & regulate local blood flow
vascular smooth muscle cells → vasoconstriction & vasodilation/relaxation

--> resistance vessels

What is the function and structure of the capillaries?

transport of gases, water, solutes & cells across endothelium
very thin-walled, highly permeable (continuous < fenestrated < sinusoid) 

--> exchange vessels
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What is the function and structure of the veins and vena cava?

collection blood
low pressure, high compliance/flexibility: “volume reservoir”
relatively thin-walled, valves assist in unidirectional blood flow back to the heart

--> capacitance vessels

What are the main functions of the endothelium?

- epithelium of blood vessels; semi-selective barrier between the vessel lumen and surrounding tissue (edema)
- blood pressure control (= regulation of vascular tone) through vasoconstriction & - dilation (hypertension, ischemia)
- prevention of blood loss (= hemostasis) by vascular spasm, platelet aggregation (primary hemostasis) & blood coagulation (secondary hemostasis) (hemophilia, thrombosis)
- inflammation & leukocyte recruitment to (i) promote clearance of dead tissue & wound healing after tissue injury and (ii) elimination of infectious agents & infected cells (atherosclerosis)
- lipid metabolism (atherosclerosis)
- angiogenesis (retinopathy)

How is vascular tone regulated?

Via intrinsic and extrinsic mechanisms
- intrinsic (autoregulation) = metabolic control (production of substances) and myogenic (stretch)
- extrinsic = neuronal and hormonal

What are metabolic controls that cause vasodilatation?

Decrease of O2, and increase in CO2, H+ and K+, adenosine, NO and prostaglandins

-> released into the extracellular space to reach other target cells, but also via gap junctions

What are hormonal controls that cause vasodilation?

ANP

What are hormonal controls that cause vasoconstriction?

Ang II, antidiuretic hormone, epinephrine and norepinephrine

What is sGC? And what are the domains of this enzyme?

Soluble guanylate cyclase, that converts GTP into cGMP (stimulated by NO because this disrupts the interaction between His105 and Fe2+ which is required for maximal enzyme activity).

domains:
- N-terminal regulatory or HNOX domain = NO receptor/sensor
- central PAS domain = heterodimerization and signal propagation
- central a-helical/coiled-coil domain = heterodimerization and signal propagation
- C-terminal catalytic domain = TGP -> cGMP

What happens in endothelial dysfunction with oxidative stress?

ENOS uncoupling
-> BH4 is converted to BH2 by ONOO- (peroxynitrite) which is produced due to smoking, hypertension, diabetes, hypercholesterolemia, aging

--> no vasodilatation

What can be used to treat eNOS uncoupling?

NO donors which can activate sGC and vasodilatation can happen
Example is nitroglycerin

Besides NO, there are other vasoactive compounds which?

EDRF: shear stress and agonists initiate the production of PGI2, H2O2, K+ etc.
EDCFs: pressure and agonists initiate the production of PGs and ET1

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