8 Arterioles and Vascular Resistance Flashcards
What 4 main factors control vasocontriction?
endothelial factors
local mechanisms
central neural mechanisms
hormonal mechanisms
How is NO synthesised?
synthesised by nitric oxide synthase from L arginine
What does NO do?
What is its’ half life?
decreases intracellular calcium levels, with a half life of <10s, acting very locally
Name 3 types of arteriole dilators
NO
Prostoglandins
Endothalial derived hyperpolarisation factor
What is the main type of vasoconstrictor?
How does it work?
endothelins, acting via intracellular calcium release
How might you treat pulmonary hypotension?
endothelin blockers
What effect do metabolic waste products have on tone?
vasodilation
What is active hypereamia?
In increase in flow dictated by an increase in metabolic waste products during exercise, for example
What is the relationship between flow and metabolic activity?
an increase in flow is directly proportional to an increase in metabolic activity
What is reactive hyperaemia?
transient increase in flow seen after a period of no flow, usually due to arterial occlusion
Describe an everyday example of reactive hyperaemia
after isotonic contraction like during weightlifting
thought to be due to the build up of metabolites during occlusion, which are washed out in hyperaemia causing vasodilation
What is the relationship between flow and perfusion pressure?
they are directly proportional
What are myogenic mechanisms?
when lumens expand, smooth muscle contracts
this is caused by calcium entry into the smooth muscle and hence depolarisation
this is called autoregulation
Which organs might have good autoregulation?
those wihch can’t tolerate a drop in blood flow when pressure fails
renal, cerebral, cardiac
What will happen if blood pressure exceeds the autoregulatory range?
because maximum vasoconstriction has already been met, there will be an increase in blood flow
