Session 6 - Control Of The CVS Flashcards
What will happen to arterial and venous pressures if CO rises at a constant TPR?
Arterial pressure will rise
Venous pressure will fall
Define Diastolic Volume
The volume of blood in the ventricle at the end of diastole
Define Systolic Volume
The volume of blood in the ventricle at the end of systole
Define Stroke Volume
The difference between end diastolic volume and end systolic volume
State and explain the relationship between venous pressure and end diastolic volume
- Higher the venous pressure, the higher the end diastolic volume
- In diastole ventricles are closed off from arteries and are connected to veins
- the amount the ventricles fills depends on the venous pressure
When plotted on a graph what is the relationship between the end is stolid volume and the venous pressure known as?
The ventricular compliance curve
Define “Pre-Load” and what is it determined by?
The end-diastolic stretch on the myocardium
Determined by venous pressure
Define “After-Load”
The force necessary to expel blood into the arteries
What is Starling’s Law?
The more the heart fills, the more it contracts (up to a point)
The harder it contracts the bigger the stroke volume
Simply: More in -> More Out
What is the relationship between venous pressure and stroke volume?
As venous pressure increases so does stroke volume up to a point.
The curve will then plateau and begin to decrease as the heart becomes overfilled and overstretched
What is contractility?
The gradient of Starling’s Curve. (Graph of venous pressure against stroke volume)
What is contractility increased by?
Sympathetic activity
How does the brain detect changes in blood pressure?
Baroreceptors in the arch of the aorta and carotid sinus
These sense changes in arterial pressure and send signals to the medulla which will send signals to the heart accordingly
What will happen to CO if venous pressure falls?
Co will fall
What will happen to CO if arterial pressure falls?
CO will rise
What is the response of the CVS after a meal?
- metabolites will cause vasodilation in the gut
- TPR falls, arterial pressure will therefore fall and venous pressures will rise
- CO will therefore increase
- this will reverse the changes in vessel pressures
How could pulmonary Oedemma be a risk during exercise?
- venous return could greatly rise and arterial pressure fall
- Outputs from both sides of the heart must be same
- massive venous return means right heart pumps more meaning left heart must also
- However if already at top of Starling’s curve the left heart can’t pump anymore so blood will accumulate in the lungs
How is a Pulmonary Oedemma prevented in response to exercise?
- Heart Rate increases
- when the venous pressure increases HR already is high
- Stroke volume kept down but CO increased
How does the CVS respond to standing up?
- central venous pressure falls as blood pools in legs (gravity)
- therefore CO decreases, therefore arterial pressure decreases
- Baroreceptors detect this fall, and cause HR to increase even though venous pressure is low
- TPR increases to defend arterial pressure
How does the CVS respond to Haemorrhage?
- Venous pressure falls so CO falls -> arterial pressure falls
- Baroreceptors detect -> HR rises, TPR rises
- increasing HR makes venous pressure even lower though
- Veno-constriction must occur to solve problem
- blood transfusion required to replace lost blood
How does the CVS respond to a long term increase in blood volume?
- Venous pressure increases -> CO increases -> arterial pressure increases
- more blood refuses to tissues which auto-regulate and increase TPR
- Arterial pressure increases further and will stay high
What will happen to arterial and venous pressures if TPR falls at a constant CO?
Arterial pressure will decrease
Venous pressure will increase
