Regulation of the cardiovascular system Flashcards

Question

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

Answer 1

A

•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)

Answer 2

A

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

Answer 3

A

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

Answer 4

A

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

Answer 5

A

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

Answer 6

A

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

Answer 7

A

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

Answer 8

A

Sympathetic nervous system is important in controlling the circulation

Parasympathetic nervous system is important in regulating heart rate

Answer 9

A

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

Answer 10

A

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

Answer 11

A

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

Answer 12

A

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

Answer 13

A

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

Answer 14

A

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

Answer 15

A

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.

Answer 16

A

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

Answer 17

A

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