Vascular control Flashcards
What is the most important factor determining resistance
Arteriolar diameter
What is blood vessel radius dependent on
- Active tension exerted by smooth muscle (vascular smooth muscle)
- Passive elastic properties of wall (elastin and collagen)
- Blood pressure inside vessel (tissue pressure outside vessel-veins)
Is wall tension greater in small vessels or large vessels
Smaller in small vessels
What increases wall tension
Increase in radius (eg aneurysm)
What can develop active tension
Smooth muscle
What does active control of vessel calibre allow
- redistribution of blood flow
- Control of pre/post capillary sphincters
- Regulation of vascular tone and control of blood pressure
What is vascular tone
Degree of constriction/dilatation
What is passive tension like and active tension like in a vasoconstrictor blood vessel
- Increased active tension
- Decreases passive tension
What is active tension and passive tension like in a vasodilator blood vessel
Decreased active tension and increased passive tension
What is vasomotor tone
The degree of tension of the smooth muscle within the walls of blood vessels (especially arterials)
What is venomotor tone
The degree of tension in the muscle coat of a vein that determines the shape of the vein
What can constriction of blood vessels do
redistribute the blood flow by changing the active properties of the smooth muscle cells (ie in exercise). Allows us to distribute blood flow to specific parts of the body where it is most metabolically active
Mechanism of vasoconstriction
1) varicosities contain neurotransmitters. There is an influx of calcium in the varicosity. This makes vesicles fuse with the membrane
2) Vesicles release noradrenaline
3) noradrenaline acts on alpha 1 adrenoceptor receptors on smooth muscle cells and cause vasoconstriction
Where is noradrenaline released from
Sympathetic nerves
What does noradrenaline act on
Alpha 1, alpha 2, and beta 2
What do the noradrenaline acting on alpha 1 and 2 adrenoceptors do
Cause vasoconstriction
What does noradrenaline acting on beta 2 adrenoceptors do
cause vasodilation
What hormones cause constriction
Noradrenaline and adrenaline, vasopressin and angiotensin
What hormones cause dilation
Noradrenaline, adrenaline, bradykinin
Mostly, what do adrenoceptors do
Cause vasoconstriction in most vascular beds
What are endothelium-derived vasorelaxants
Prostacyclin
Nitric oxide
Endothelium-derived hyperpolarising factor
What are endothelium derived vasoconstrictors
Endothelin
What does an increase in lactate cause in relation to smooth muscle contraction
Increase H+, increase in K+ and increase in adenosine causes dilatation
In systemic vasculature, what does an increase in O2 and a decrease in Co2 cause
Constriction
in systemic vasculature, what does an increase in Co2 and a decrease in O2 cause
Dilatation
In pulmonary vasculature, what does an increase in Co2 and a decrease in O2 cause
Constriction
In pulmonary vasculature, what does an increase in O2 and a decrease in Co2 cause
Dilatation
What is blood flow like in the brain
Autoregulated (it is constant) therefore there is no change in flow
What happens when there is an increase in pressure in the cerebral blood vessels
Blood vessels are stretched, and this causes vasoconstriction
What happens in the brain if blood pressure falls
Less stretch on cerebral blood vessels therefore they vasodilate. The driving force has decreased so there is an overall same blood flow
What mechanisms are primarily concerned with meeting blood flow demands of particular organs/tissues
Intrinsic mechanisms (metabolic, myogenic)
What mechanisms are primarily concerned with regulation of arterial blood pressure
Extrinsic contort mechanisms (nerves, hormones)
How much cardiac output does the Brain receive at rest
14%
What causes vasodilation in the brain
H+, K+, adenosine, hypercapnia (too much CO2), and hypoxia (not enough oxygen)
What is an important vasoconstrictor in pathological states (eg subarachnoid haemorrhage) in the brain
Endothelin
