CVS S6 - Control of the CVS Flashcards
What would happen if TPR rose and cardiac output remained constant?
Arterial pressure rises
Venous pressure falls
What would happen if TPR fell and cardiac output remained constant?
Arterial pressure falls
Venous pressure rises
What would happen if cardiac output rose and TPR remained constant?
Arterial pressure rises
Venous pressure falls
What would happen if cardiac output fell and TPR remained constant?
Arterial pressure falls
Venous pressure rises
Explain how the cardiovascular system is demand-led
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
Define end diastolic volume
The volume of blood in the ventricle at the end of diastole
Define end systolic volume
The volume of blood in the ventricle at the end of systole
Define stroke volume
The difference between end systolic volume and end diastolic volume
What affects how much the ventricles refill in diastole?
Venous pressure - the higher the pressure in the great veins, the more the ventricles will refill
Define pre-load
The end-diastolic stretch of the myocardium, determined by venous pressure
Define after-load
The force necessary to expel the blood from the ventricles into arteries
Explain Starling’s Law
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.
Define contractility
The stroke volume for a given venous pressure
NOT force of contraction
How does the sympathetic nervous system affect contractility?
Contractility is increased by sympathetic stimulation
Therefore sympathetic activity causes the heart to be more susceptible to venous pressure
How does the cardiovascular system respond to haemorrhage?
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
How can the cardiovascular system recover from haemorrhage?
Venous pressure needs to be increased
Heart rate needs to be decreased
Achieve this by veno-constriction and blood transfusion to replace lost fluid
Discuss the response of the cardiovascular system to a long term increase in blood volume
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
What affects autonomic stimulation to the heart?
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
What would be the effect of decreased venous pressure?
Reduced cardiac output due to decreased preload
What would be the effect of increased venous pressure on cardiac output?
Increased cardiac output due to increased preload
What would be the effect of increased arterial pressure on cardiac output?
Decreased cardiac output due to increased after-load
What would be the effect of decreased arterial pressure on cardiac output?
Increased cardiac outflow due to decreased after-load
Discuss the initial response of the cardiovascular system to eating a meal
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
Describe the effects of the initial response of the CVS to eating a meal and how the system stabilises
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
Discuss the challenges of the cardiovascular system during exercise
Enormous increase in demand
Muscle pumping causes extra blood to return to the heart
Discuss the challenges of the cardiovascular system during exercise
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
How are the challenges of exercise met by the cardiovascular system?
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
How does the cardiovascular system respond to standing up?
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
What happens if the baroreceptor reflex doesn’t work?
Postural hypotension
If severe, syncope
