Nervous and hormonal control of vascular tone Flashcards
what is vascular tone?
the degree of constriction experienced by a blood vessel relative to its maximally dilated state
what is the main thing that controls TPR?
vascular tone
what is a resistance vessel?
what is a capacitance vessel?
resistance = arteriole capacitance = vein
paracrine, autocrine and endocrine
paracrine = if a cell sends a signal to an adjacent cell
autocrine = if a cell sends a signal to itself
endocrine = if a cell signals another cell that is far away
vascular control can be controlled by 2 different types: what are they?
intrinsic/local control
-regulate local blood flow to organs/tissues
extrinsic control
- regulates TPR to control blood pressure
- brain function selectivity alters blood flow to organs according to need (e.g. during exercise, thermoregulation)
name the types of intrinsic control:
- myogenic response (resistance vessels)
- paracrine and autoregulation agents (NO, PG’s, endothelin, K+, H+) (both)
- physical factors (both)
- temperature (both)
- sheer stress (both)
name the types of extrinsic control:
- parasympathetic, sympathetic, sensory vasodilator nerves (resistance vessels)
- sympathetic vasoconstrictor nerves (both)
- adrenaline (both)
- angiotensin II (both)
- vasopressin (both)
- ANP (atrial natriuretic peptide) (both
what is the myogenic response?
how the arteries and arterioles react to increase/decrease in BP
how do nerves affect vascular control?
o Vasoconstrictors – e.g. noradrenaline
o Vasodilators – e.g. Ach, NO
how do hormones affect vascular control?
o Vasoconstrictors – e.g. adrenaline, angiotensin II, vasopressin
o Vasodilators – e.g. anti-natriuretic peptide (ANP)
what is the most widespread and important extrinsic control?
Sympathetic Vasoconstrictor System
what in the role of the brain in terms of information from the nervous system?
nervous system information is integrated by the brain
how are arterioles constantly held between contraction and dilation?
- constant sympathetic NA effect (pulse every sec) sending NA to the vessels- makes them want to constrict
- at the same time, there is background production of NO by the endothelial cells in the vessels- makes them want to dilate
where does info from the CVLM in the brain go?
RVLM
what are the CVLM and RVLM?
2 sensors in the brain that integrate signals to the sympathetic nervous system, partly automatic but also process info from higher sensors in the brain
explain how sympathetic vasoconstrictor nerves work?
1) An AP moves down the axon and arrives at a varicosity (little pearl shape)
2) Depolarisation at the varicosity activates voltage gated Ca2+ channels
3) Entry of Ca2+ causes release of neurotransmitters – mainly NA
4) NA can bind to β1 receptors on heart which increases HR and SV
5) NA diffuses to the vascular smooth muscle cells where it binds mainly to:
a. α1 – contraction
b. α2 – contraction
c. β2 – relaxation
6) The NA is then taken up again and recycled or broken down
- Adrenaline from the adrenal glands can be released into the circulation can also act at α1 (contraction) or β2 (relaxation) receptors on smooth muscle
how can the smooth muscle be constricted or relaxed?
NERVOUS - NA released due to depolarisation
HORMONAL - Adrenaline released from the adrenal glands
how can NA release be modulated?
- Angiotensin II
- Metabolites
- NA can negatively feedback itself
how does Angiotensin II affect NA release?
Angiotensin II acts on AT1 receptors, causing an increase in NA release and vasoconstriction, causing an increase in BP.
how do metabolites affect NA release?
Metabolites (inflammatory mediators) have their own channels on the varicosity, inhibiting release of NA and causing vasodilation- prevent vasoconstriction to maintain blood flow
K+, adenosine, histamine & serotonin inhibit NA release by decreasing cAMP levels
how can NA modulate itself?
NA can negatively feedback itself via α2 receptors to limit to its own release
where does lots of modulation occur?
at the neurotransmitter level at the varicosity
role of the CVLM?
provides central control of blood flow/blood pressure
what do sympathetic vasoconstrictor nerves do?
Innervate most arterioles & veins of the body
sympathetic nerve activity is tonic - what does this mean and why is it important?
tonic means 1 action potential per second
o Tonic sympathetic activity sets vascular tone