nervous and hormonal control of vascular tone Flashcards
What is involved in intrinsic control of blood vessels
- myogenic response
-paracrine & autocrine - physical factors -temperature & shear pressure
-regulates blood flow to organs and tissues
-vasodilators-inflammation , local metabolites ( nitric oxide, prostaglandin, endothelin, potassium and hydrogen ions )
What is involved in extrinsic control of blood vessels
- parasympathetic , sympathetic and sensory vasodilator nerves
-sympathetic vasoconstrictor nerves
-brain Function selectivity alters blood flow to organs according to need
In the nerves
Vasoconstrictor- noradrenaline
Vasodilators - Ach, nitric oxide
In hormones
Vasoconstrictor- adrenaline, angiotensin II
Vasodilator- atrial natriuretic peptide (ANP)
Steps for constriction in sympathetic vasoconstrictor nerves
- action potential moves down axon and arrive at varicosity
- depolarisation at the varicosity activating voltage gated calcium channels
- entrance of calcium causes release neurotransmitters- mainly noradrenaline
- noradrenaline diffuses to vascular smooth muscle cells binds to mainly alpha one , some alpha two and beta two
-noradrenaline is taken up again and recycled or broken down
What is the release of noradrenaline modulated by
Angiotensin II acting on AT1 receptor
what is varicosity
veins that are bulging and swollen
what happens when noradrenaline is released in the varicosity detail
noradrenaline is released which causes vasodilation via alpha 1 receptors
alpha 2 receptors provide negative feedback so that the noradrenaline doesnt continuously lead to constriction
what is the rostal ventrolateral medulla controlled by and its role
caudal ventrolateral medulla and hypothalamus and provides central control of blood flow and blood pressure
how is the sympathetic nerve activity described as
tonic, 1 action potential per second
in sympathetic vasoconstrictor nerves what does noradrenaline activate and cause
activates alpha 1 adrenoreceptors on vascular smooth muscle cells causing vasoconstriction
main roles of sympathetic vasoconstrictor nerves
-distinct sympathetic pathways ( switching on vasoconstriction in some vessels )
-control resistance arterioles (produces vascular tone allows vasodilation or vasoconstriction , maintains arterial blood pressure and blood flow to brain myocardium
-precapillary vasoconstriction ( downstream capillary pressure drop so increased absorption of interstitial fluid into blood plasma to maintain blood volume)
-control venous blood volume ( venoconstriction leads to decreased venous blood volume increasing venous return , increases stroke volume via starlings law
when does vasodilation usually occur
when vascular tone produced by sympathetic vasoconstrictor nerves is inhibited
are specific vasodilator nerves sympathetic or parasympathetic
parasympathetic
in vasodilator nerves what are blood vessels innervated by
parasympathetic cholingeric fibres , they release acetylcholine which binds to muscarinic receptors on the smooth muscle or endothelium
example of parasympathetic vasodilators
-salivary glands- release ach and VIP
-pancreas and intestinal mucosa - release VIP , both need high blood flow to maintain fluid secretion.
male gentalia - erectile tissue , release nitric oxide by sympathetic nerves causes production of cGMP which leads to vasodilation
examples of sympathetic vasodilators
-skin -sudomotor fibres, release Ach , VIP causing vasodilation via nitric oxide associated with sweating
what does sympathetic activity vasoconstriction
-reduces blood flow , limit sweat production and limit cooling
what is the lewis triple response
inflammation
-redness caused by capillary vasodilation
-flare-redness in surrounding area due to arteriolar dilation mediated by axon reflex
-wheal- exudation of extracellular fluid from capillaries and venules
hormones involved in vasoconstriction
-adrenaline
-angiotensin II
-vasopressin - ADH
hormone involved in vasodilation
-ANP - atrial natriuretic peptide
where is adrenaline released from and when
adrenal medulla via action of acetylcholine on nicotinic receptors
during
-exercise
-flight-fight-fear response
-hypotension
-hypoglycaemia
main role of adrenaline (epinephrine)
-glucose mobilisation
-stimulation of heart rate & contractility during normal exercise
-vasodilation of coronary and skeletal muscle arteries
action of noradrenaline on resistance vessels
-activate alpha 1 Gq
-leads to phospholipase c
-leads to PIP2 converting to IP3 and DAG
-calcium ions are released
-smooth msucle contraction
action of adrenaline on resistance vessels
-activates beta 1 and beta 2 Gs
-leads to adenylate cyclase
-converts ATP to cAMP
-leads to beta 1 heart contraction
-beta 2 smooth muscle relaxation vasodilation
what does adrenaline have a higher affinity for
higher affinity for beta over alpha , mainly acts at beta 2 to dilate vessels
what does noradrenaline have a higher affinity for
higher affinity for alpha, mainly acts at alpha 1 to constrict vessels
role of beta 1 on heart
increases rate and force of contraction
role of alpha 2
inhibits adenylate cyclase , reduces calcium ions , inhibits release of noradrenaline from varicosity
steps in renin angiotensin aldosterone system (RAAS)
-low sodium load , detected at macula densa
-decreased pressure at juxtagomerular cells
-leads to renal sympathetic activity
-renin released
-conversion of angiotensinogen to angiotensin I
-occurs in lung vascular endothelium
-angiotensin 2 is produced from angiotensin 1
-aldosterone released
-central effects eg thirst
-vasoconstriction raises TPR
-release of vasopressin (ADH)
-Aldosterone leads to renal sodium chloride and water retention -raised blood volume
how are vasopressin stimulated to be released
-dehydration/ haemorrhage NTS inhibition is switched off and CVLM stimulates vasopressin
when there is an increase in osmolarity what does this lead to
-vasopressin synthesised in hypothalamus
-released from vesicles in posterior of pituitary gland
-leads to insertion of water aquaporin channels into apical membrane of renal collecting tubule
-collecting duct epithelial cells allowing water to move out of the nephron and back into the blood stream
-reabsorption of fluid by kidney and vasoconstriction both maintain blood pressure
what is ANP released and secreted by
-released by atrial myocytes
-secreted by increased filling pressures which stimulate stretch receptors
where does ANP act
acts at ANP receptors on vascular smooth muscle cells increasing cGMP pathway (like nitric oxide)
what does systemic vasodilation oppose
action of noradrenaline, RAAS, ADH
