Regulation of the cardiovascular system Flashcards
What are the equations for stroke volume, cardiac output and BP?
What effects Venous Volume distribution?
What is the central venous pressure?
The amount of blood flowing back to the heart determines …………… …………. (using Starling’s Law of the Heart)
•Venous volume distribution affected by
–peripheral venous “tone”
–gravity
–skeletal muscle pump
–breathing
- Central venous pressure (mean pressure in the right atrium) determines the amount of blood flowing back to the heart.
- The amount of blood flowing back to the heart determines stroke volume (using Starling’s Law of the Heart)
Veins: Constriction determines …………. and …………….
Arterioles: Constriction determines………..
List 3 things
Flow changed primarily by altering ……………. ………….
Veins: Constriction determines compliance and venous return
Arterioles: Constriction determines
•blood flow to organs they serve
•mean arterial blood pressure
•the pattern of distribution of blood to organs
Flow changed primarily by altering vessel radius
List 4 things venous volume distribution is affected by?
What does central venous pressure determine?
Veins are the storage vessels for blood volume - they have capacitance
Venous volume distribution is affected by:
Peripheral Venous Tone
Gravity
Skeletal Muscle Pump
Breathing
Central venous pressure determines the amount of blood flowing back to the heart
The amount of blood flowing back to the heart determines stroke volume (Starling’s Law)
Amount of blood returning to the heart determines the amount of stretch and hence determines the force of contraction
Flow Control
Mainly determined by the …………..
Constriction can be variable and this determines compliance and hence ………….. …………..
The extent of the constriction is determined by the pattern of organisation of innervation to particular vascular beds i.e. the number of …………..………….. will affect the blood flow to an organ
Flow is primarily changed by altering ………….. …………..
Flow Control
Mainly determined by the ARTERIOLES
Constriction can be variable and this determines compliance and hence venous return
The extent of the constriction is determined by the pattern of organisation of innervation to particular vascular beds i.e. the number of adrenoreceptors will affect the blood flow to an organ
Flow is primarily changed by altering vessel radius
Name 3 ways of regulating blood flow?
Ways of regulating flow
Local Mechanisms
Intrinsic to the smooth muscle itself or closely associated
Hormonal
Circulating hormones
Autonomic Nervous System
Innervates arterioles and veins to produce constriction or dilation
Define autoregulation?
When the blood pressure drops, there will be a gradual decrease in resistance and hence a gradual increase in flow ?
Explain the two theories for this mechanism?
WHITE line = what happens with no autoregulation
When the blood pressure drops, there will be a gradual decrease in resistance and hence a gradual increase in flow
There are TWO theories for this mechanism:
Myogenic Theory = smooth muscle fibres respond to stretch (stress operated ion channels) - as pressure rises, the muscle fibres start contracting to keep flow constant
Metabolic Theory = if the vessels supplying a particular vascular bed contract, the flow to the vascular bed decreases and the vascular bed produces MORE METABOLITES - as more metabolites are produced, it feeds back on the vessel that’s supplying the bed and causes vasodilation and hence allows more flow to the vascular bed and the metabolites which triggered this response are washed away
Autoregulation can be changed by injury to the vessel - when a vessel is injured, platelets aggregate and they release serotonin which is a powerful vasoconstrictor which will constrict the injured vessel
Substances released from the endothelium also have a role in regulating blood flow
Nitric Oxide - plays a key role in vasodilation
Prostacyclin + Thromboxane A2 (vasodilator and vasoconstrictor respectively)
Endothelins - potent vasoconstrictors
What do kinins tend to do?
Where are ANPs released from and what does it do?
List 3 Circulating Vasoconstrictors?
Systemic Regulation of Blood Flow by Hormones
Kinins
Have complex interactions with the Renin-Angiotensin System
Tend to relax vascular smooth muscle
ANP (Atrial Natriuretic Peptide)
Circulating peptides that are secreted from the cardiac atria
As the atria stretch they release more ANP which causes vasodilation
Circulating Vasoconstrictors
Noradrenaline
Is the sympathetic system important in controlling the circulation ot regulating heart rate?
Is the parasympathetic system important in controlling the circulation ot regulating heart rate?
Sympathetic nervous system is important in controlling the circulation
Parasympathetic nervous system is important in regulating heart rate
Sympathetic Innervation of Blood Vessels
Sympathetic nerve fibres innervate ALL VESSELS EXCEPT ………………. (and precapillary sphincters and some metarterioles)
Distribution of sympathetic nerve fibres is NOT even - more sympathetic nerve fibres innervate vessels supplying the ……………, ………, ……………. and ………… and fewer innervate the skeletal muscle and the brain
So there is more potential to constrict the blood going to these places so that we can divert blood to the organs that we need more
Circulating adrenaline binds with high affinity to smooth muscle ………..-adrenoreceptors to cause vasodilation in some organs, however the effect is very concentration-dependent
At high concentrations, adrenaline can bind to ……….. adrenoreceptors which can override the vasodilatory effects of the………..-adrenoreceptor stimulation and produce vasoconstriction
The constriction you see in blood vessels is an ………..-adrenoreceptor effect
Sympathetic Innervation of Blood Vessels
Sympathetic nerve fibres innervate ALL VESSELS EXCEPT CAPILLARIES (and precapillary sphincters and some metarterioles)
Distribution of sympathetic nerve fibres is NOT even - more sympathetic nerve fibres innervate vessels supplying the kidney, gut, spleen and skin and fewer innervate the skeletal muscle and the brain
So there is more potential to constrict the blood going to these places so that we can divert blood to the organs that we need more
Circulating adrenaline binds with high affinity to smooth muscle beta-2-adrenoreceptors to cause vasodilation in some organs, however the effect is very concentration-dependent
At high concentrations, adrenaline can bind to ALPHA adrenoreceptors which can override the vasodilatory effects of the beta-2-adrenoreceptor stimulation and produce vasoconstriction
The constriction you see in blood vessels is an alpha-1-adrenoreceptor effect
Where is the vasomotor centre (VMC) located?
What does the VMC consists of (3 parts)?
Higher centres in the brain (such as the ………………….) can exert excitatory and inhibitory effects on the VMC
Lateral Portions of the VMC controls heart activity by influencing ……….. ………… and ………………
VMC is located bilaterally in the reticular substance of the medulla and the lower third of the pons
The VMC consists of a:
Vasoconstrictor Area (Pressor)
Vasodilator Area (Depressor)
Cardioregulatory Inhibitory Area
Higher centres in the brain (such as the hypothalamus) can exert excitatory and inhibitory effects on the VMC
Lateral Portions of the VMC controls heart activity by influencing heart rate and contractility
Medial Portions of the VMC transmits signals via the vagus nerve to the heart that tends to decrease heart rate
The VMC allows an anticipatory response to exercise - your heart rate and ventilation rate will go up slightly before exercise because of these higher sensors in the brain
Nervous control of blood vessel diameter
Blood vessels receive ……………….. postganglionic innervation
The neurotransmitter involved is ……………………..
There is ALWAYS some …………. activity
At baseline, there is a certain frequency of the impulses which maintains vasomotor …………….
If you increase the nerve traffic then you can ……………… the vessel
If you decrease the nerve traffic then you can …………….. the vessel
So by altering this activity you can make the vessel either …………… or ……………..
There is NOT much ………………… innervation of the vascular system
Blood vessels receive sympathetic postganglionic innervation
The neurotransmitter involved is NORADRENALINE
There is ALWAYS some tonic activity
At baseline, there is a certain frequency of the impulses which maintains vasomotor tone
If you increase the nerve traffic then you can constrict the vessel
If you decrease the nerve traffic then you can dilate the vessel
So by altering this activity you can make the vessel either dilate or constrict
There is NOT much parasympathetic innervation of the vascular system
Summary: Control of Blood Vessel Radius
THREE areas allow control of vessel radius:
Local Controls (Autoregulation)
Circulating Hormones
Sympathetic Vasoconstrictor Nerves
How does parasympathetic nerves decreases the heart rate?
How does sympathetic nerves increase the heart rate?
What is the normal heart rate with no innervation?
List 3 things that increase heart rate?
We change the heart rate by dual innervation - sympathetic and parasympathetic
The sinoatrial nodal cells receive sympathetic and parasympathetic innervation
Normal resting heart rate is around 70 bpm
Parasympathetic slows heart rate down because acetylcholine decreases the gradient of the pacemaker potential - this means that the potential takes longer to reach threshold and fire
Sympathetic increases heart rate because adrenaline and noradrenaline increases the gradient of the pacemaker potential so threshold is reached more quickly
If we cut the sympathetic nerves we lose the ability to increase heart rate so heart rate falls
With no innervation, the normal activity is around 100 bpm
Which of the following increase blood vessel radius?
1) Noradrenaline released from sympathetic nerves innervating the blood vessels
2) Nitric Oxide
3) Angiotensin II
4) Bradykinin
5) Viagra-sildenafil
2,4,5
Controlling Force of Contraction
Force of contraction can be increased by …………… Law
Sympathetic activity will also increase the …………. of contraction
Noradrenaline binds to Adrenoreceptors which increases the amount of …………. which activates …………. which phosphorylates the…………. .. ……….. …………. and the …………. . ……….. . …………. …………. and ………….
So you get MORE CALCIUM INFLUX and more calcium taken back up into the stores
Action of noradrenaline on ………….-receptors in the heart will increase contraction
So we can alter heart rate and strength of contraction by sympathetic activity
Strength of contraction CAN NOT be changed by parasympathetic activity
Controlling Force of Contraction
Force of contraction can be increased by Starling’s Law
Sympathetic activity will also increase the force of contraction
Noradrenaline binds to Adrenoreceptors which increases the amount of cAMP which activates PKA which phosphorylates the L-type calcium channels and the SR calcium release channel and SERCA
So you get MORE CALCIUM INFLUX and more calcium taken back up into the stores
Action of noradrenaline on beta-1-receptors in the heart will increase contraction
So we can alter heart rate and strength of contraction by sympathetic activity
Strength of contraction CAN NOT be changed by parasympathetic activity
Stroke volume can be increased by:
Increased Sympathetic Activity
Plasma Adrenaline
Intrinsic control of stroke volume: venous return which sets the end-diastolic volume (stretch) which increases the force of contraction
We can get more blood back to the heart (increase venous return) if we increase respiratory movements - decreasing intrathoracic pressure helps the filling of the heart
What in the diagram below is effected by the sympathetic NS?
Where are baroreceptors located?
Baroreceptors in the carotid bodies feedback to the vasomotor centre via what nerve?
The aortic arch baroreceptors feedback to the vasomotor centre via what nerve ?
Baroreceptors are in the aortic arch and in the carotid sinus (carotid bodies)
Baroreceptors in the carotid bodies feedback to the vasomotor centre via the glossopharyngeal nerve
The aortic arch baroreceptors feedback to the vasomotor centre via the vagus nerve
Summary of the feedback nerves to the vasomotor centre:
Aortic Arch Baroreceptor = Vagus Nerve
Carotid Sinus Baroreceptors = Glossopharyngeal Nerve
Caroreceptors respond to changes in ……………. …………….
Carotid sinus baroreceptors respond to pressures between 60 and 180 mmHg.
Baroreceptors respond to changes in arterial pressure.
Baroreceptors reflex is most sensitive at pressures around 90 – 100 mmHg.
What happens when a receptor sees an increase in pressure?
Increase in baroreceptor firing = ……………. in in parasympathetic activity
Increase in baroreceptor firing = …………….. in sympathetic activity
Parasympathetic stimulation of the heart occurs via the ………… nerve which causes a decrease in heart rate
There is a decrease in sympathetic stimulation to the heart which causes decreased ………… ………… and ……….. ………….
Decreased sympathetic stimulation to the blood vessels causes ……………………
Reciprocal Innervation
When the receptor sees an increase in pressure it fires more - the nerve activity is increased which fires directly to the blue synapse and mediates an increase in parasympathetic nerve activity
Increase in baroreceptor firing = Increase in in parasympathetic activity
The sympathetic nerves are connected via a series of inhibitory interneurones which slows down the tonic activity
Increase in baroreceptor firing = DECREASE in sympathetic activity
Parasympathetic stimulation of the heart occurs via the vagus nerve which causes a decrease in heart rate
There is a decrease in sympathetic stimulation to the heart which causes decreased heart rate and stroke volume
Decreased sympathetic stimulation to the blood vessels causes vasodilation
The increase in baroreceptor firing is fed back to the …………. …………. which triggers increased traffic in the …………. ………….
REMEMBER: parasympathetic activity reflects exactly what happens in terms of baroreceptor activity
Increase in parasympathetic activity causes an increase in …………. production in the …………. which decreases the gradient of the pacemaker potential and causes a decrease in …………. ………….
Increase in baroreceptor activity also decreases the …………. nerve traffic which also brings about a decrease in ………….………….
Sympathetic cardiac nerves also have an effect on the force of contraction - so less innervation from sympathetic nerves leads to a decrease in the force of contraction
Decrease in sympathetic activity also leads to an increase in ………….………….
These changes in heart rate, contraction and dilation leads to a DECREASE IN BLOOD PRESSURE
The increase in baroreceptor firing is fed back to the vasomotor centre which triggers increased traffic in the vagus nerve
REMEMBER: parasympathetic activity reflects exactly what happens in terms of baroreceptor activity
Increase in parasympathetic activity causes an increase in acetylcholine production in the SAN which decreases the gradient of the pacemaker potential and causes a decrease in heart rate
Increase in baroreceptor activity also decreases the sympathetic nerve traffic which also brings about a decrease in heart rate
Sympathetic cardiac nerves also have an effect on the force of contraction - so less innervation from sympathetic nerves leads to a decrease in the force of contraction
Decrease in sympathetic activity also leads to an increase in vessel radius
These changes in heart rate, contraction and dilation leads to a DECREASE IN BLOOD PRESSURE
Control of venous return
Feedback for blood pressure control
Mean Systemic Arterial Pressure = Cardiac Output x Total Peripheral Resistance
This whole response is all about MAINTAINING BLOOD PRESSURE
When you lose blood, your blood pressure is maintained because of these mechanisms but if you lose a lot of blood very quickly then these mechanisms will be insufficient
If the radius of a blood vessel is decreasesmby half, by what fraction does the blood flow change?
1/16
