cardiac control 2

Question 1

stroke volume =

Answer 1

EDV - ESV

Question 2

cardiac output =

Answer 2

SV x HR

Question 3

blood pressure =

Answer 3

Q(cardiac output) x TPR(total peripheral resistance)

Question 4

venous volume distribution is affected by?

Answer 4

peripheral venous tone, gravity, skeletal muscle pump and breathing

Question 5

what does central venous pressure determine?

Answer 5

determines the amount of blood flowing back to the heart

this in turn determines stroke volume

Question 6

flow is primarily changed by?

Answer 6

altering vessel radius

since constriction reduces compliance and venous return

Question 7

F = (Poiseuille’s equation)

R inversely proportional to?

Answer 7

§ Remember the two important equations and relationships:
𝐹= Δ𝑃/𝑅
𝑅 ∝ 1/𝑟^4

Question 8

Autoregulation =

Answer 8

Autoregulation = the intrinsic capacity to compensate changes in perfusion pressure by changing vascular resistance.

Question 9

Myogenic Theory –

Answer 9

Smooth muscle responds directly to tension changes in the vessel wall e.g. stretch sensitive receptors.

Question 10

Metabolic Theory –

Answer 10

As blood flow decreases, metabolites accumulate and vessels dilate in response.

Question 11

Injury Theory –

Answer 11

Serotonin release from platelets causes vasoconstriction.

Question 12

examples of local mechanisms regulating blood flow

Answer 12

autoregulation
myogenic theory
metabolic theory
injury

Question 13

local endothelium derived hormones

Answer 13

1. Nitric Oxide (NO) – vasodilation, produced from arginine, NO diffuses into vascular smooth muscle cells
2. Prostacyclin- vasodilator, synthesised from prostacyclin precursor, also has an antiplatelet and anticoagulant effects
3. Thromboxane A2 – vasoconstrictor, synthesised from prostacyclin precursor, also heavily synthesised in platelets
4. Endothelins – POTENT vasoconstrictors. generated from the nucleus of endothelial cells- has minor vasodilator effects but principally a vasoconstrictor

Question 14

circulating non-endothelium derived hormones

Answer 14

1. Kinins: binds to receptors on endothelial cells and stimulate NO synthesis- vasodilator effects
2. ANP (arterial natriuretic peptide): Secreted from the atria in response to stretch. Vasodilator effects to reduce BP.
3. Circulating Vasoconstrictors: ADH/Vasopressin from posterior pituitary in response to high blood osmolality. binds to V1 receptors on smooth muscles and causes vasoconstriction.
   Angiotensin II from renin secretion: potent vasoconstrictor product from the renin-angiotensin-aldosterone axis. Also stimulates SNS activity and ADH secretion.

Question 15

Autonomic nervous system includes 2 branches

Answer 15

parasympathetic and sympathetic

Question 16

SNS is important in?

Answer 16

SNS is important in controlling the circulation.

Question 17

PNS is important in?

Answer 17

§ PNS is important in regulating heart rate.

Question 18

Sympathetic innervation to blood vessels:

Answer 18

Sympathetic innervation to blood vessels:
§ SNS nerve fibres innervate ALL vessels except capillaries, pre-capillary sphincters and some metarterioles.
§ Distribution of fibres is variable, more fibres innervate vessels to kidney, gut spleen and skin and less innervate skeletal muscle and the brain.

Question 19

pre-ganglionic fibres use what as their neurotransmitter?

Answer 19

ACh

Question 20

PNS post ganglionic NT

Answer 20

ACh

Question 21

SNS post ganglionic NT

Answer 21

NA

Question 22

noradrenaline prefers to bind to what receptors?

Answer 22

preferentially binds to alpha-1 adrenoceptors to cause smooth muscle contraction/vasoconstriction.

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

Question 23

vasomotor centre location

Answer 23

VMC is located bilaterally in the reticular substance of the medulla and the lower third of the pons

Question 24

The VMC consists of a:

Answer 24

Vasoconstrictor Area (Pressor)

Vasodilator Area (Depressor)

Cardioregulatory Inhibitory Area

Question 25

what do each of the different parts do? - higher centres of the brain - lateral portions of the VMC - medial portion of the VMC

Answer 25

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

Question 26

nervous control of vessel diameter- how does it work?

Answer 26

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

Question 27

Control of Blood Vessel Radius THREE areas allow control of vessel radius:

Answer 27

Local Controls (Autoregulation) Circulating Hormones Sympathetic Vasoconstrictor Nerves

Question 28

cardiac innervation by dual innervation | what are they and how do they work?

Answer 28

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

Question 29

with no cardiac innervation what is the normal activity?

Answer 29

100bpm

Question 30

controlling force of contraction can be increased using which law?

Answer 30

Force of contraction can be increased by Starling's Law

Question 31

how does controlling force of contraction work using sympathetic activity?

Answer 31

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

Question 32

controlling stroke volume by two methods

Answer 32

Increased Sympathetic Activity Plasma Adrenaline since: 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

Question 33

what occurs as part of the flight or flight response?

Answer 33

We can get rapid changes in RESPIRATORY MOVEMENT, PLASMA ADRENALINE and INCREASE SYMPATHETIC ACTIVITY as part of the fight or flight response

Question 34

where are baroreceptors located?

Answer 34

aortic arch and in the carotid sinus (carotid bodies)

Question 35

Baroreceptors in the carotid bodies feedback to

Answer 35

Baroreceptors in the carotid bodies feedback to the vasomotor centre via the glossopharyngeal nerve

Question 36

The aortic arch baroreceptors feedback to

Answer 36

The aortic arch baroreceptors feedback to the vasomotor centre via the vagus nerve

Question 37

how do baroreceptors work?

Answer 37

change firing in response to arterial pressure

Question 38

Carotid sinus baroreceptors respond to pressure between

Answer 38

Carotid sinus baroreceptors respond to pressure between 60 and 80 mmHg

Question 39

Baroreceptor reflex is most sensitive around

Answer 39

Baroreceptor reflex is most sensitive around 90-100 mmHg

Question 40

Increase in baroreceptor firing =

Answer 40

Increase in in parasympathetic activity as When the receptor sees an increase in pressure it fires more - the nerve activity is increased 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 to heart, arterioles and veins

Question 41

increased parasympathetic stimulation of the heart

Answer 41

decreases heart rate

Question 42

where are cardioregulatory and vasomotor centres located

Answer 42

medulla oblongata

Question 43

Increased Blood Pressure = | mechanics

Answer 43

huge increase in firing activity throughout from the baroreceptor 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

Question 44

which nerves are involved in control of venous return

Answer 44

sympathetic vasoconstrictor nerves

Question 45

Mean Systemic Arterial Pressure =

Answer 45

Cardiac Output x Total Peripheral Resistance