CVS 9 - Regulation of the CVS Flashcards
Recall the key equations for SV, CO, MBP, flow (Q), Resistance
SV = EDV - ESV CO = SV x HR MBP = CO x TPR Q = difference in P / R R proportional to 1/r^4
The volume of blood in our veins depends on:
Peripheral venous tone
Gravity
Skeletal muscle pump
Breathing (respiratory pump)
NOTE
Venous return determines SV (Starling’s law)
How do we alter flow? How is this done (3) ?
Alter flow by changing vessel radius
This is done in 3 ways:
LOCAL MECHANISMS – intrinsic to the smooth muscle
SYSTEMIC REGULATION – due to circulating hormones
AUTONOMIC NERVOUS SYSTEM
Describe local mechanism to regulate blood flow
Autoregulation: the intrinsic capacity to compensate for changes in perfusion pressure by changing vascular resistance.
This means that if Perfusion Pressure drops,, local mechanisms cause resistance to decrease for blood to flow better. (Q=P/R)
What are the 2 theories of autoregulation?
MYOGENIC THEORY
The smooth muscles themselves are sensitive to stretch.
Say pressure drops the tension (or stretch) of the vessels fall.
The smooth muscles senses this and vasodilates as a result to INCREASE FLOW
METABOLIC THEORY
When pressure drops and flow reduces the blood accumulates in the vessels
In the blood are a bunch of metabolites which act on the vascular smooth muscle
Thus, causing vasodilation
When the flow increases again those metabolites are taken away by the blood
State two molecules produced in the endothelium that cause vasodilation.
Nitric Oxide and Prostacyclin
State two molecules produced in the endothelium that cause vasoconstriction.
Thromboxane A2
Endothelin-1
State five hormones that regulate blood flow.
Vasodilators
Atrial Natriuretic Peptide (ANP) (from atria as a response to RA stretch)
Kinins (e.g. bradykinin) - oppose ANG-II
Vasoconstrictors:
Vasopressin (ADH) from posterior pituitary
Angiotensin II
Noradrenaline released from adrenal medulla (not ANS)
What neurotransmitter do all parasympathetic neurones release?
ACh
What neurotransmitters could sympathetic neurones release?
Noradrenaline, adrenaline or acetylcholine (sweat glands)
Which vessels do not have sympathetic innervation?
Capillaries, pre-capillary sphincters and metarterioles
sympathetic innervates all the others including large veins
Which particular organ also has sympathetic innervation?
The heart
NOTE
Distribution to other organs is variable.
To which receptors does NA bind to?
Noradrenaline binds to α1-adrenoceptors to cause smooth muscle contraction and vasoconstriction.
To which receptors does A bind to?
To beta2 receptors on smooth muscle to cause vasodilation.
HOWEVER at HIGH CONC. A binds to aplha1 and alpha2 receptors which overrides vasodilator effect of Beta2 and causes vasoconstriction.
The distribution of sympathetic nerve fibres is not even. Where do you find more sympathetic nerve fibres?
There are more sympathetic nerve fibres in the spleen, gut, kidneys and skin because there is more potential to divert blood away from these organs without causing damage. There are fewer sympathetic fibres in the skeletal muscle and brain.