CVS Session 6- Control Of Cardiac Output Flashcards
What happens to venous and arterial pressure if TPR rises?
Venous pressure decreases
Arterial pressure increases
What happens to the venous and arterial pressures if TPR falls?
Venous pressure rises
Arterial pressure decreases
What happens to arterial and venous pressure if the cardiac output rises?
Arterial pressure rises
Venous pressure decreases
What happens to arterial and venous pressure if cardiac output falls?
Arterial pressure decreases
Venous pressure increases
Why does venous pressure rise when arterial pressure and cardiac output are low?
Because less blood is being pumped out of the heart and therefore back to the heart. For this little blood to return to the heart, high pressure is required so it can reach it.
What is the relationship between TPR and the body’s demand for blood?
They are inversely proportional
What is demand-led pumping?
The response of the heart to arterial and venous pressures to bring the pressures back to normal.
What is the pressure response after a meal if cardiac output is constant?
- gut needs more blood
- local vasodilators dilate arterioles
- TPR falls
- arterial pressure falls and venous pressure rises
When does the heart fill?
Diastole
What is the stroke volume?
The difference between the end systolic volume and the end diastolic volume
When do the ventricles stop filling?
When the walls have stretched enough to cause an intraventricular pressure which is equal to the venous pressure.
What is the relationship between venous pressure and ventricular filling?
The higher the venous pressure, the more the ventricles will fill (within limits)
If venous pressure increases, what happens to the stroke volume?
It increases
What is “pre-load” and what is it determined by?
It is the end diastolic stretch of myocardium.
Determined by the venous pressure
What is “after-load” and what does it determine?
It is the force necessary to expel blood out of the heart into the arteries during systole.
It determines what happens during systole
What is starling’s law?
Increases in venous pressure will lead to an increased stroke volume (within limits).
More in=more out
On the Starling curve, why does the stroke volume only increase to a certain point with venous pressure?
Due to the constraints of the pericardium- the heart can only fill to a certain point.
What factors lead to an increased stroke volume? (4)
- increased venous pressure
- a fall in TPR
- increased sympathetic activity
- decreased arterial pressure
What is contractility?
It is the relationship between force of contraction and venous pressure, for any given fibre length.
What is the end systolic volume?
The amount that the ventricle empties
What does the end systolic volume depend on?
- how hard it is to eject blood from the ventricles
- how hard they contract
What is force of contraction determined by?
- end diastolic pressure
- contractility
If arterial pressure falls, what will happen to the end systolic volume and stroke volume?
End Systolic volume - fall
Stroke volume - increase
What is the function of a baroreceptor?
To detect changes in arterial pressure.
What is the consequence of a fall in arterial pressure?
Increased heart rate, stroke volume and contractility
When arterial pressure is low, how is heart rate increased?
Reducing parasympathetic activity
Increasing sympathetic activity
When arterial pressure is low, how is contractility increased?
Increasing sympathetic activity
What is the Bainbridge reflex?
If venous pressure rises, heart rate rises because venous pressure in the right atrium is detected and parasympathetic activity is reduced.
When does cardiac output rise? (2)
- when venous pressure rises
- when arterial pressure falls
