CVS control mechanisms

Question 1

What is the organisation of the sympathetic nervous system?

Answer 1

Branch of autonomic nervous system
Fight or flight response
Needed for controlling circulation via thoracic and lumbar vertebra T1 to L2
Short pre-ganglionic fibres
Long post-ganglionic fibres

Question 2

What are the neurotransmitters that act within the sympathetic nervous system?

Answer 2

Acetylcholine in a nicotinic receptor

Causes release of noradrenaline

Question 3

What is renin and when is it released?

Answer 3

Enzyme released to cleave angiotensinogen to Ang I
Released from juxtaglomerular cells that line the afferent arterioles in kidneys when:
BP decreases - detected by macula densa cells in DCT that reabsorb more Na+ when low pressure which releases prostaglandins to stimulate renin production and release
Stimulated by SNS

Question 4

What is the role of angiotensin II?

Answer 4

Cause vascular smooth muscle contraction
Causes PPG to secrete ADH
Causes adrenal gland to secrete aldosterone that increases reabsorption of water in kidneys =increased stroke volume

Question 5

What is the synthesis pathway of angiotensin II?

Answer 5

Angiotensinogen from liver cleaved by renin from kidneys to Ang I
Blood enters lungs where ACE converts Ang I to Ang II
Ang II enters zona glomerulosa of adrenal cortex to stimulate aldosterone production

Question 6

Explain the anatomy of baroreceptors

Answer 6

Specialised cells that can detect BP

Firing mirrors BP

Question 7

Define cardiac output

Answer 7

Stroke volume x HR
Volume of blood pumped by heart per minute
(approx 5L)

Question 8

Define stroke volume

Answer 8

EDV-ESV
Volume of blood pumped by heart per beat
approx 70 ml

Question 9

Define mean arterial pressure

Answer 9

Cardiac output x TPR
or
DBP + 1/3Pulse pressure
(pulse pressure = SBP-DBP)

Question 10

Explain the response of the cvs to standing

Answer 10

Standing causes increased hydrostatic pressure
Blood transiently pools in veins due to high compliance
Causes decrease in venous return which must be compensated otherwise reduction in CO and BP

Question 11

Explain the response of the cvs to exercise

Answer 11

Increased exercise = increased venous return due to skeletal muscle pump work in legs
this increases EDV ∴ increases sympathetic activity of heart
∴increase in contractility and SV
∴Increased CO

Question 12

Where does noradrenaline bind in the heart and what does it cause?

Answer 12

Binds to β1 adrenoreceptors on the heart

Increases force of contraction and HR ∴ larger stroke volume and increased contractility

Question 13

Where is noradrenaline released from, what does it bind to and what does this cause?

Answer 13

Released from long post-ganglionic fibres of the SNS
Binds to α1-adrenoceptors
Causes smooth muscle contraction and vasoconstriction

Question 14

What does the SNS innervate?

Answer 14

Heart and all vessels except capillaries

Innervation is variable with kidneys, gut and spleen being highly innervated and brain and muscle less so

Question 15

Where is the vasomotor centre located and what are its main features?

Answer 15

Bilateral structure within medulla and lower 1/3 of pons in brain
3 main areas:
-Vasoconstrictor area
-Vasodilator area
-Cardioregulatory inhibitory area
Influenced by higher brain centres e.g. hypothalamus

Question 16

What is the purpose of the vasomotor centre?

Answer 16

Excitatory or inhibitory
Transmits impulses to blood vessels
Lateral portions influence HR and contractility
Medial portion transmits via vagus nerve to heart to lovwer HR

Question 17

Explain nervous control of blood vessel diameter.

Answer 17

Always some level of tonic activity to the vasculature from the SNS
Activating or decreasing baseline leads to constriction or dilation
Generally no PNS innervation to the vascular system

Question 18

How can venous return be controlled?

Answer 18

Increased by skeletal muscle pumping/respiratory movements
Increased blood volume
Increase SNS vein activation

Question 19

How does noradrenaline cause increased force of contraction?

Answer 19

Upregulates cAMP which causes increased activation of L type Ca2+ channels ∴ increased Ca2+ uptake and influx

Question 20

Where do carotid sinus baroreceptors send impulses?

Answer 20

Down glossopharyngeal PNS afferent to the VasoMotor centre

Question 21

Where do aortic arch baroreceptors send impulses?

Answer 21

Down vagus nerve PNS afferent to VasoMotor centre

Question 22

What causes increased rate of baroreceptor firing and what happens when baroreceptor firing rate increases?

Answer 22

If BP increases, baroreceptor firing increases
Increases PNS efferent firing down vagus nerve to increase PNS activity at the heart to slow the rate by increasing length of a sinoatrial node action potential
This increases inhibitory interneuron firing ∴ inhibiting tonic SNS activity ∴ decreasing SNS activity to slow HR and cause vasodilation

Question 23

What is the response of the nervous system to haemorrhage?

Answer 23

Decreased stroke volume = decreased baroreceptor firing
Reduced PNS&increased SNS firing to increase contractility and ∴ stroke volume
Increased SNS discharge to veins to increase tone and pressure/return
Increased SNS discharge to arterioles to increase vasoconstriction
Increased Mean Arterial Pressure due to increased CO by stroke volume and EDV from increased venous return and increased TPR by arteriolar constriction

Question 24

Where is blood pressure measured?

Answer 24

In brachial artery on the upper arm

Question 25

What is used to measure blood pressure?

Answer 25

Cuff, sphygmomanometer and stethoscope

Question 26

How is blood pressure measured?

Answer 26

Cuff is inflated to obstruct blood flow by increasing pressure until the cuff exceeds arterial pressure
Release of cuff slowly whilst listening for turbulent flow - first korotkoff sound indicates SBP
Eventually artery no longer occluded and flow returns to normal laminar flow - sound disappearing = DBP

Question 27

How can values obtained from manual blood pressure measurement be used to calculate mean arterial pressure?

Answer 27

DBP + 1/3Pulse pressure

pulse pressure = SBP-DBP