Local regulation of blood flow - supply and demand Flashcards
haemodynamics
physical study of flowing blood and all the solid structures through which it flows
in poiseuille formula Q( flow) is proportional to what
change in pressure x vessel radius to the power of 4 divided by /////
blood viscosity x vessel length
lood flows from higher pressure system largest being arotia down to lower pressure in capillaries and then to lowest point in the vena cava.
what are the 4 physical determinants of blood flow through the vascular system
pressure change
vessel radius
blood viscosity
vessel length
As fluid becomes thicker (viscosity increases), flow decreases in proportion
What conditions may result in increased blood viscosity
Polycythemia Hypercholesterolaemia Diabetes Smoking, alcoholism, severe dehydration, diuretics (Anaemia can reduce blood viscosity)
Q=1/n
Flow is inversely proportional to the viscosity of the fluid
Moderate anaemia can actually increase tissue oxygen delivery by lowering blood viscosity and increasing flow through the vascular bed
Transfusions of cold, concentrated red blood cells run slowly
which factor is most important in the regulation of blood flow?
vessel radius
this causes the resistance
What property of the vasculature determines vessel radius?
Vascular smooth muscle tone (vasoconstriction/dilatation)
A change in vascular tone of which vessel type is the most influential in regulating blood flow to tissues/organs?
Arterioles are the main sites of resistance to blood flow within the vascular system
Arterioles have a thick layer of smooth muscle (tunica media) in their walls, highly innervated by what
by sympathetic nerve fibres
what arterioles vasoconstriction what happens to resistance and blood flow to the capillaries
resistance goes up and blood flow to the capillaries decreases
in the regulation of blood flow what two mechanisms controls whole body circulation
neurological - autonomic NS
Humoral via angiotensine II , vasopressin , adrenaline, atrial natriuretic peptide
in the regulation of blood flow what mechanism controls regional/ organ blood flow
Local(metabolic and myogenic)
what type of receptor does adrenaline have a greater affinity for creating what effect
Beta-2 so vasodilation
What type of receptor does nor-adrenaline have a greater affinity for creating what effect
Alpha-1 so vasoconstriction - there are no alpha-1 receptors however in cerebral arteriolar smooth muscle
A high dose of adrenaline is used in clinical settings to do what?
increase blood pressure through vasoconstriction
how is the increase of blood pressure achieved
Through binding to both α1 and β2 adrenergic receptors on vascular smooth muscle
Adrenaline has higher affinity for β2 receptors but there are more α1 receptors overall across the vascular bed, so a high dose of adrenaline leads to overall vasoconstriction and an increase in arterial blood pressure. Physiological levels of adrenaline cause vasodilatation through binding to β2 receptors within skeletal muscle vascular beds, decreasing blood pressure.
obviously cell respiration and metabolic demand goes up so Lowered partial pressure of oxygen
this triggers release of NO what does this do
vasodilator - relax underlying smooth muscle
what is active hyperaemia
caused by increased of blood flow to organs - blood vessels widen to increase supply of blood. - local intrinsic mechanism of increasing blood flow to tissues to meet metabolic demand
what does NO do
Local chemical and physical changes due to increased metabolic demand
Increased shear stress on endothelium
what does endothelin do
and what stimulates and inhibits it
A potent vasoconstrictor
Stimulated by angiotensin II, vasopressin
Inhibited by NO
what do vascular endothelia growth macros do
promote angiogenesis - Long-term adaptation to decreased blood flow to a tissue
the intrinsic myogenic response is called what
auto-regulation - important in kidneys
vascular tone is controlled by 3 influences yes or no
Neurogenic (sympathetic NS)
Humoral (vasoactive substances)
Local (intrinsic) mechanisms
Local/intrinsic control of blood flow includes what
Active hyperaemia – responds to changes in demand
Autoregulation – responds to changes in supply