Control Of The CVS Flashcards
At a constant total peripheral resistance, what happens to arterial and venous pressure if cardiac output increases?
Arterial pressure will increase
Venous pressure will fall
At a given cardiac output, what happens to arterial and venous pressure if total peripheral resistance falls?
Arterial pressure will fall and venous pressure will rise
Define stroke volume
Difference between end diastolic volume and end systolic volume
Define end diastolic volume
Volume of blood in the ventricle at the end of diastole
What is end systolic volume?
Volume of blood in the ventricle at the end of systole
When do the ventricles stop filling?
Until the walls stretch enough to produce an intra-ventricular pressure equal to venous pressure
What determines how much the heart fills in diastole?
The venous pressure. The higher the venous pressure, the more the heart fills.
What is the curve for the relationship between venous pressure and ventricular volume?
The ventricular compliance curve
Define pre-load
End diastolic stretch of the myocardium
What is afterload?
The force necessary to expel blood into the arteries
What makes the ventricles contract harder?
The more they stretch before contracting, so the more the heart fills. Therefore a bigger stroke volume
What does a rise in venous pressure lead to?
A rise in stroke volume due to increased filling of the ventricles and harder contraction.
Describe the curve showing the relationship between venous pressure and stoke volume at a constant afterload
Curve steeply increases, then slows down as it gets to the peak. Begins to curve downwards. (Looks like a tilted walking stick)
What is contractility?
The stroke volume you get for a given venous pressure
What increases the contractility?
Sympathetic activity
What controls autonomic outflow?
Signals from baroreceptors which are located in the arch of the aorta and the carotid sinus
Where do baroreceptors send their signals to?
The medulla
If venous pressure rises, what happens to cardiac output?
It rises
If arterial pressure rises, what happens to cardiac output?
It falls
How does the CVS respond to eating a meal?
Increased activity of the gut so releases metabolites ➡️ local vasodilation
TPR falls
➖INCREASED VENOUS PRESSURE, rise in cardiac output
➖DECREASED ARTERIAL PRESSURE, rise in cardiac output
Extra pumping of the heart reduces venous pressure and raises arterial pressure
Demand in met and system is stable
Response of CVS to exercise?
Muscle pumping forces extra blood back to the heart
Increase in heart rate straight away to prevent ventricle over filling
When venous pressure starts to rise, CO is already high
Stroke volume is kept down while cardiac output is increased
Demand is met and system is stable
What would happen if the heart rate didn’t speed up in advance when exercising?
Venous pressure would rise too much and arterial pressure would fall too low.
This would push Starling’s curve of venous pressure and stroke volume onto the flat part and ventricles would stretch
Risk of pulmonary oedema
Response to CVS on standing up?
Blood pools in superficial veins so central venous pressure falls
➡️fall in cardiac output and arterial pressure
Arterial and venous pressure change in same direction
Baroreceptors detect fall in arterial and raise heart rate.
TPR to skin and gut increases to defend arterial pressure
What happens when there is a haemorrhage?
Reduction in blood volume ➡️ reduction in venous pressure ➡️ cardiac output falls ➡️ arterial pressure falls
What is the body’s response to bleeding?
Baroreceptors detect fall in arterial pressure and increase heart rate
TPR is increased
Increased heart rate reduces venous pressure further and heart rate can become very high
Venous pressure is increased by vasoconstriction and auto-transfusion
What is auto-transfusion?
When fluid from tissue moves into capillaries due to a low hydrostatic pressure
What is blood volume controlled by?
The kidney
What happens if blood volume is increased long term?
Venous pressure rises
Cardiac output increases
Arterial pressure rises
Forces more blood through tissues and increase in TPR
Arterial pressure rises further and stays up
