Nervous And Hormonal Control Of Vascular Tone Flashcards
What are the local controls of vascular tone?
Myogenic responses, paracrine and autocrine and physical factors (temp/shear stress)
What are the extrinsic controls of vascular tone?
Parasympathetic, sympathetic and sensory vasodilator nerves, sympathetic vasoconstrictor nerves, adrenaline, angiotensin II, vasopressin and atrial natriuretic peptide
What does paracrine affect?
Things very close to the source
What does autocrine mean?
A cell producing a substance that affects itself
How does local control of vascular tone work?
Regulates local blood flow to organs/tissues and is important for regional hyperaemia.
Vasodilators are used
What does extrinsic vessel control regulate?
Total peripheral resistance to control blood pressure. The brain selectively alters blood flow to veins according to need
What causes extrinsic control in nerves?
Vasoconstrictors like noradrenaline
Vasodilators like acetylcholine and nitric oxide
What hormones cause extrinsic control in blood vessels?
Vasoconstrictors like adrenaline and angiotensin I
Vasodilators like anti-natriuretic peptide
What is the pathway for the sympathetic vasoconstrictor system from the brain to the sympathetic ganglia?
Signal comes from the medulla oblongata down the main excitatory drive. Splits at the thoracic (T1-L2) spinal cord and either goes down a sympathetic preganglionic fibre or into the adrenal medulla
What do varicosities contain?
- angiotensin II that act is on AT1 receptors to increase noradrenaline
- metabolites prevent vasoconstriction to maintain blood flow
- noradrenaline can also negatively feedback itself via alpha 2 receptors to limit its own release
What are sympathetic vasoconstrictor nerves controlled by?
The brainstem
The rostral ventrolateral medulla is controlled by other areas like the caudal ventrolateral medulla and hypothalamus
What does tonic mean?
One action potential per second
What activity sets vascular tone?
Tonic sympathetic activity
What are the main roles of sympathetic vasoconstrictor nerves?
- Distance sympathetic pathways innervate different tissue
- precapillary vasoconstriction
- control resistance arterioles
- controls venous blood volume
What does pre capillary vasoconstriction lead to?
Downstream capillary pressure drop so increased absorption of interstitial fluid into blood plasma to maintain blood volume
How do control resistance arterioles work?
Allowing vasodilation to occur and controlling total peripheral resistance
Maintains arterial blood pressure and blood flow to the brain, myocardium and kidneys
How does control of venous blood volume work?
Venoconstriction leads to decreased venous blood volume increasing venous return. This increases stroke volume via starlings law
How does vasodilation normally occur?
By an inhibition of the sympathetic vasoconstrictor nerves
What type of tissues contain vasodilator nerves?
Tissues that have a specific function controlling a specific vascular bed
What part of the nervous system do vasodilator nerves generally belong to?
Parasympathetic
What happens when blood vessels are innervated by parasympathetic cholinergic fibres?
Release acetylcholine which then binds to muscarinic receptors on the smooth muscle and/or endothelium
What can M3 receptors on the vascular endothelium be coupled to?
The formation of nitric oxide which causes vasodilation
What type of receptor vasodilates in response to ACh?
M5 muscarinic
What is an example of a sympathetic vasodilator nerve?
Skin (sudomotor fibres)
How do the sudomotor fibres work?
Release ACh and vasoactive intestinal peptide, causing vasodilation via NO associated routes
What does increased blood flow cause in the skin?
More sweat and allows heat loss
What has some control over the sudomotor fibres in the head, face and upper chest and what do they cause?
Emotional centres are involved in blushing
What glands release ACh and vasoactive intestinal peptide?
Salivary glands
What releases just vasoactive intestinal peptide?
The pancreas and intestinal mucosa
What do male genitalia release for vasodilation?
NO
How does vasodilation work in male genitalia?
NO causes production of cGMP which leads to vasodilation .
How does sildenafil (viagra) work?
Inhibits the breakdown of cGMP by phosphodiesterase 5
What are sensory vasodilator fibres (nociceptive C fibres) involved in?
Stimulation of sensory axon reflex by trauma or infection etc
What do nociceptive C fibres cause release of?
Substance P or calcitonin gene- related peptide (CGRP)
What do nociceptive C fibres act on?
Mast cells to release histamine or the endothelial and vascular smooth muscle
What are the three things in the Lewis triple response?
Local redness, wheal and flare
How does the Lewis triple response work?
When there is trauma, an action potential will be sent to both the dorsal root ganglion and down the axon collateral. The axon collateral then causes release of substance P and mast cell degranulation
What are the hormonal vasoconstrictors?
Adrenaline, angiotensin II and vasopressin
What are the hormonal vasodilators?
Atrial natriuretic peptide, insulin, estrogen, relaxin
When is adrenaline released?
During exercise and fight or flight response
Hypotension and hypoglycaemia
What are the main roles of adrenaline?
Glucose mobilisation, stimulation of heart rate and contractility during normal exercise and as a vasodilator of coronary and skeletal muscle arteries
What does adrenaline do in most tissues (and with what receptor)?
Vasoconstrict alpha 1
What does noradrenaline do in most tissues (and with what receptor)?
Vasoconstrict alpha 1
What does adrenaline do in skeletal muscle and coronary circulation(and with what receptor)?
Vasodilation beta 2
What does noradrenaline do in skeletal muscle and coronary circulation (and with what receptor)?
Vasoconstrictor alpha 1
What are the effects of IV adrenaline on circulation?
Cardiac output goes up
TPR goes down
Not much effect on blood pressure
What is the effect of IV noradrenaline on circulation?
Increase in blood pressure
Decrease in heart rate
Increase in TPR
Cardiac output decrease
What does RAAS stand for?
Renin-angiotensin-aldosterone system
Give the steps of RAAS
Stimulus causes kidneys to release renin, which combines with angiotensinogen in the liver to produce angiotensin I
Angiotensin converting enzyme then converts that to angiotensin II
What does NTS stand for?
Nucleus tractus solitarius
How is vasopressin released?
Stretch receptors in the left atrium send continuous signals to the NTS. NTS sends out inhibitory signals to the CVLM, which stimulates the pituitary gland to release vasopressin
What is the hypothalamus response to vasopressin stimulated by?
An increase in osmolarity
Where is vasopressin released from and what does this cause?
Posterior of the pituitary gland which causes increased reabsorption of fluid by kidney and causes vasoconstriction. Both effects maintain blood pressure
Where is the NTS?
In the medulla
What does ANP stand for?
Atrial natriuretic peptide
What is AMP released by?
Specialised atrial myocytes
What do stretch receptors act as?
ANP receptors on vascular smooth muscle cells increasing the cGMP pathway
