CVS S6 - Control of the CVS

Question 0

What would happen if TPR rose and cardiac output remained constant?

Answer 0

Arterial pressure rises

Venous pressure falls

Question 1

What would happen if TPR fell and cardiac output remained constant?

Answer 1

Arterial pressure falls

Venous pressure rises

Question 2

What would happen if cardiac output rose and TPR remained constant?

Answer 2

Arterial pressure rises

Venous pressure falls

Question 3

What would happen if cardiac output fell and TPR remained constant?

Answer 3

Arterial pressure falls

Venous pressure rises

Question 4

Explain how the cardiovascular system is demand-led

Answer 4

TPR changes in response to metabolic demand (vasodilator metabolites)
Change in TPR alters arterial and venous pressure
The alteration causes change in cardiac output
This makes the system stable

Question 5

Define end diastolic volume

Answer 5

The volume of blood in the ventricle at the end of diastole

Question 6

Define end systolic volume

Answer 6

The volume of blood in the ventricle at the end of systole

Question 7

Define stroke volume

Answer 7

The difference between end systolic volume and end diastolic volume

Question 8

What affects how much the ventricles refill in diastole?

Answer 8

Venous pressure - the higher the pressure in the great veins, the more the ventricles will refill

Question 9

Define pre-load

Answer 9

The end-diastolic stretch of the myocardium, determined by venous pressure

Question 10

Define after-load

Answer 10

The force necessary to expel the blood from the ventricles into arteries

Question 11

Explain Starling’s Law

Answer 11

It states that the more the ventricles fill, the harder they contract. The harder they contract, the greater the stroke volume.
Simplified: more in, more out.

Question 24

Define contractility

Answer 24

The stroke volume for a given venous pressure

NOT force of contraction

Question 25

How does the sympathetic nervous system affect contractility?

Answer 25

Contractility is increased by sympathetic stimulation

Therefore sympathetic activity causes the heart to be more susceptible to venous pressure

Question 26

How does the cardiovascular system respond to haemorrhage?

Answer 26

Reduced blood volume lowers venous pressure
So cardiac output falls
So arterial pressure falls
Baroreceptors detect this
Medulla causes increased heart rate
This further reduces venous pressure
System unstable, problem worsens as HR increases and venous pressure decreases

Question 27

How can the cardiovascular system recover from haemorrhage?

Answer 27

Venous pressure needs to be increased
Heart rate needs to be decreased
Achieve this by veno-constriction and blood transfusion to replace lost fluid

Question 28

Discuss the response of the cardiovascular system to a long term increase in blood volume

Answer 28

Increased venous pressure
Cardiac output rises
Arterial pressure increases
More blood perfumes tissues
Tissues auto regulate and increase TPR
Arterial pressure rises and stays high

Question 29

What affects autonomic stimulation to the heart?

Answer 29

Baroreceptors in the arch of the aorta and the carotid sinus send information on arterial pressure to the medulla oblongata
The medulla then controls autonomic outflow

Question 30

What would be the effect of decreased venous pressure?

Answer 30

Reduced cardiac output due to decreased preload

Question 31

What would be the effect of increased venous pressure on cardiac output?

Answer 31

Increased cardiac output due to increased preload

Question 32

What would be the effect of increased arterial pressure on cardiac output?

Answer 32

Decreased cardiac output due to increased after-load

Question 33

What would be the effect of decreased arterial pressure on cardiac output?

Answer 33

Increased cardiac outflow due to decreased after-load

Question 34

Discuss the initial response of the cardiovascular system to eating a meal

Answer 34

Increased metabolic activity of the gut causes local vasodilator metabolites to be released
This causes decreased TPR
So decreased arterial pressure and increased venous pressure

Question 35

Describe the effects of the initial response of the CVS to eating a meal and how the system stabilises

Answer 35

Increased venous pressure causes increased cardiac output
Decreased arterial pressure triggers increased heart rate and cardiac output
The extra pumping of the heart decreases venous pressure and increases arterial pressure
Therefore the demands are met and the system is stable

Question 36

Discuss the challenges of the cardiovascular system during exercise

Answer 36

Enormous increase in demand

Muscle pumping causes extra blood to return to the heart

Question 37

Discuss the challenges of the cardiovascular system during exercise

Answer 37

Venous pressure could greatly increase, leading to overfilling and stretching of the heart
If stroke volume becomes too high, the right and left ventricles can become unmatched so there is a risk of pulmonary oedema

Question 38

How are the challenges of exercise met by the cardiovascular system?

Answer 38

Overfilling of ventricles prevented by raising the heart rate
So stroke volume kept down and cardiac output still increased
Therefore demand met so system is stable

Question 39

How does the cardiovascular system respond to standing up?

Answer 39

Upon standing, blood pools in the superficial veins of the legs due to gravity
So central venous pressure falls
So cardiac output falls
So arterial pressure falls
Baroreceptors detect this
Heart rate is increased by the medulla oblongata
Venous pressure still low so increased TPR
System stabilises

Question 40

What happens if the baroreceptor reflex doesn’t work?

Answer 40

Postural hypotension

If severe, syncope