Intrinsic and extrinsic control of the circulation
Arteries vs arterioles
Large arteries
large elastic component as these are first and foremost transport vessels
Arterioles
large muscular component for flow control
Vascular tone
Smooth muscles constrict and control blood flow
vascular tone regulates:
- arterial blood pressure
- capillary recruitment and capillary pressure
- central venous pressure
Intrinsic and extrinsic control of vascular tone
Control hierarchy
in order of first steps
- local response
- endothelial secretions, vasoactive metavolites, autacoids
- extrinsic factors
Intrinsic mechanisms
Myogenic response
vessels respond directly to a change in pressure by vasocontriction or dilation (bayliss myogenic response)
more endothelial shear stress triggers vessels to make NO which is a vasodilator as well as other things
Paracrine factors (endothelial secretions, vasoactive metabolites, autacoids)
metabolic regulation
production of metabolism leads to changes in the vessel diameter CO lactic acid metabolites etc are dilators o2 is a constrictor
this allows muscle etc to get more blood
Endothelial derived factors
constrictors
- endothelin
- angiotensin II dilators
- NO
- Prostacyclin
- endothelial derived hyperpolarising factor
- adenosine
NO production
pregnancy shear stress drugs
Physical factors
reactive hyperaemia
after an occlusion in a vessel there is dilation downstream to the occlusion. this enables high perfusion after enabling flow again
Extrinsic mechanisms
Vasodilator nerves
release noradrenaline in the tunica media releases ACh
Sympathetic vasoconstrictor nerves (widespread)
increase sympathetic activity leads to vasoconstriction reduced sympathetic activity leads to vasodilation
endocrine factors
releases na and adrenaline into the blood vasopressin angiotensin II atrial netriuretic hormone
