CVS 9 - Regulation of the CVS

Question 1

Recall the key equations for SV, CO, MBP, flow (Q), Resistance

Answer 1

SV = EDV - ESV
CO =  SV x HR
MBP = CO x TPR
Q = difference in P / R
R proportional to 1/r^4

Question 2

The volume of blood in our veins depends on:

Answer 2

Peripheral venous tone
Gravity
Skeletal muscle pump
Breathing (respiratory pump)

NOTE
Venous return determines SV (Starling’s law)

Question 3

How do we alter flow? How is this done (3) ?

Answer 3

Alter flow by changing vessel radius
This is done in 3 ways:
LOCAL MECHANISMS – intrinsic to the smooth muscle
SYSTEMIC REGULATION – due to circulating hormones
AUTONOMIC NERVOUS SYSTEM

Question 4

Describe local mechanism to regulate blood flow

Answer 4

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

This means that if Perfusion Pressure drops,, local mechanisms cause resistance to decrease for blood to flow better. (Q=P/R)

Question 5

What are the 2 theories of autoregulation?

Answer 5

MYOGENIC THEORY
The smooth muscles themselves are sensitive to stretch.
Say pressure drops the tension (or stretch) of the vessels fall.
The smooth muscles senses this and vasodilates as a result to INCREASE FLOW

METABOLIC THEORY
When pressure drops and flow reduces the blood accumulates in the vessels
In the blood are a bunch of metabolites which act on the vascular smooth muscle
Thus, causing vasodilation
When the flow increases again those metabolites are taken away by the blood

Question 6

State two molecules produced in the endothelium that cause vasodilation.

Answer 6

Nitric Oxide and Prostacyclin

Question 7

State two molecules produced in the endothelium that cause vasoconstriction.

Answer 7

Thromboxane A2

Endothelin-1

Question 8

State five hormones that regulate blood flow.

Answer 8

Vasodilators
Atrial Natriuretic Peptide (ANP) (from atria as a response to RA stretch)
Kinins (e.g. bradykinin) - oppose ANG-II

Vasoconstrictors:
Vasopressin (ADH) from posterior pituitary
Angiotensin II
Noradrenaline released from adrenal medulla (not ANS)

Question 9

What neurotransmitter do all parasympathetic neurones release?

Answer 9

ACh

Question 10

What neurotransmitters could sympathetic neurones release?

Answer 10

Noradrenaline, adrenaline or acetylcholine (sweat glands)

Question 11

Which vessels do not have sympathetic innervation?

Answer 11

Capillaries, pre-capillary sphincters and metarterioles

sympathetic innervates all the others including large veins

Question 12

Which particular organ also has sympathetic innervation?

Answer 12

The heart
NOTE
Distribution to other organs is variable.

Question 13

To which receptors does NA bind to?

Answer 13

Noradrenaline binds to α1-adrenoceptors to cause smooth muscle contraction and vasoconstriction.

Question 14

To which receptors does A bind to?

Answer 14

To beta2 receptors on smooth muscle to cause vasodilation.
HOWEVER at HIGH CONC. A binds to aplha1 and alpha2 receptors which overrides vasodilator effect of Beta2 and causes vasoconstriction.

Question 15

The distribution of sympathetic nerve fibres is not even. Where do you find more sympathetic nerve fibres?

Answer 15

There are more sympathetic nerve fibres in the spleen, gut, kidneys and skin because there is more potential to divert blood away from these organs without causing damage. There are fewer sympathetic fibres in the skeletal muscle and brain.

Question 16

Where is the vasomotor centre located?

Answer 16

VMC is located bilaterally within medulla & lower ⅓ of pons 
3 areas:
- vasodilator (depressor)
- vasoconstrictor (pressor)
- cardioregulatory inhibitory area

The role of the VMC is to transmit signal to almost all vessels.
The lateral portions control HR and contractility.
Medial portions transmit signals via the vagus nerve to the heart -> decrease HR

Question 17

Describe nervous control of blood vessel diameter

Answer 17

There is always some level of tonic activity to the vasculature
Activating or decreasing this tonic baseline leads to constriction/dilation
Generally there is NO PARASYMPATHETIC innervation to vascular system
Transmitter = NA

Question 18

What effects does the sympathetic nervous system have on the cardiovascular system?

Answer 18

Increased sympathetic activity increases heart rate, increases force of contraction and decreases the vessel radius (increases resistance)

Question 19

What effect does the parasympathetic nervous system have on the cardiovascular system?

Answer 19

It decreases heart rate

Causes vasoconstriction of the coronary arteries

Question 20

Other than decreased sympathetic activity, increased sympathetic activity, what increases HR?

Answer 20

Increased plasma adrenaline

Question 21

Describe the mechanism of action of noradrenaline on the heart.

Answer 21

Sympathetic nerves can increase the heart’s force of contraction. They release NA.
Noradrenaline binds to the beta-1 adrenergic receptor on myocyte, which causes activation of adenylate cyclase and the upregulation of cAMP leading to the activation of PKA. PKA phosphorylates, hence activates, the L-type calcium channel, Sarco/endoplasmic calcium ATPase (SERCA), SR calcium release channel,

Therefore,
Calcium influx increases
Calcium uptake into intracellular stores

Question 22

What are the three ways in which stroke volume can be increased?

Answer 22

Starling’s Law (increased EDV by increased venous return to the heart + increased respiratory movements which decrease introthoracic pressure which assists in increased EDV)
Increased plasma adrenaline
Increased sympathetic innervation

Question 23

How do respiratory movements affect the cardiac output?

Answer 23

Inspiring decreases the intrathoracic pressure meaning that the pressure on the blood vessels is decreased so the blood flows more easily into the heart and hence it increases the stretch on the heart (preload) so EDV increases so cardiac output increases (Starling’s Law)

Question 24

What nerves carry information from the two baroreceptors to the vasomotor centre?

Answer 24

Carotid Bodies - Glossopharyngeal nerves

Aortic arch- Vagus nerve

Question 25

What are the 2 baroreceptors?

Answer 25

Aortic arch

One on each carotid sinus

Question 26

What is the consequence of increased baroreceptor activity?

Answer 26

Parasympathetic activity mirrors baroreceptor activity. Increases baroreceptor activity leads to increased parasympathetic activity and decreased sympathetic activity. The increase in parasympathetic activity leads to a reduction in heart rate so a decreased in BP (as increased baroreceptor activity = increased BP)

Question 27

What are the effects of a decrease in sympathetic activity?

Answer 27

Decrease in sympathetic activity decreases heart rate and decreases force of contraction of the heart. This also increases the blood vessel radius and decreases resistance.

Question 28

What is the point in this whole response?

Answer 28

To maintain blood pressure