11 - Regulation of the CVS Flashcards
Give the equation to calculate mean systemic arterial pressure
Mean BP = CO x TPR
Mean systemic arterial pressure = cardiac output x total peripheral resistance
Give 4 factors that affect venous volume distribution
- peripheral venous tone
- gravity
- skeletal muscle pump
- breathing
What determines venous return to the heart?
central venous pressure
State Starling’s Law (with reference to the heart)
the amount of blood returning to the heart (venous return) determines the stroke volume
Which vessels mainly determine flow control?
arterioles (change constriction- this is affected by the number of adrenoreceptors)
What are the 3 mechanisms of regulating blood flow
- local mechanisms (intrinsic)
- hormonal (extrinsic)
- autonomic nervous system (extrinsic)
Define autoregulation
the intrinsic capacity to compensate for changes in perfusion pressure by changing vascular resistance
(i.e. to maintain the flow even if the pressure changes)
When BP drops, what happens to resistance and flow?
there is a gradual decrease in resistance and hence, a gradual increase in flow
How does injury change autoregulation?
when a vessel is injured, platelets aggregate and release serotonin, which is a powerful vasoconstrictor
State two molecules produced in the endothelium that cause vasodilation.
NO and prostacyclin
What is the role of kinins?
vasodilators
What does ANP stand for?
What are they?
Where are they produced?
Atrial Natriuretic Peptide
vasodilators
released from the cardiac atria as they stretch
Give the name of 3 circulating vasconstrictors
vasopresssin (released from the posterior pituitary)
angiotensin II
noradrenaline
What is the length of the nerves in the parasympathetic nervous system?
long preganglionic fibre
short postganglionic fibre
Which vessels to sympathetic nerve fibres not innervate?
capillaries (and precapillary sphincters and some metarterioles)
How does the sympathetic nervous system effect blood vessels?
NOTE: there is not much parasympathetic innervation of the vascular system
causes vasoconstriction
What are the 3 areas of the Vasomotor Centre?
- vasocontrictor area (pressor)
- vasodilator area (depressor)
cardioregulatory inhibitory area
Which areas of the brain can effect the VMC?
higher centres in the brain (e.g. hypothalamus)
NOTE: this allows an anticipatory response to exercise i.e. the ventilation rate will go up slightly before exercise
What do the lateral portions of the VMC control?
control heart activity by influencing heart rate and contractility
What do the medial portions of the VMC control?
transmit signals via the vagus nerve to the heart that decreases heart rate
What innervation do the blood vessels receive?
sympathetic post-ganglionic innervation
NOTE MUCH PARASYMPATHETIC INNERVATION OF THE VASCULAR SYSTEM
There is always some tonic activity- at baseline, there is a certain frequency of impulses which maintain vasomotor tone. What happens when the frequency of this nerve traffic increases or decreases?
increases - constriction
decrease - dilation
What systems innervate the heart rate?
sympathetic and parasympathetic (DUAL INNERVATION)
to the sinoatrial node
What is normal resting HR?
70 bpm
Give the mechanism of the parasympathetic pathway
acetylcholine deacreases the gradient of the pacemaker potential (so the potential takes longer to reach threshold and fire)
Give the mechanism of the sympathetic pathway
adrenaline and noradrenaline increase the gradient of the pacemaker potential so the threshold is reached even more quickly
