Control Of The CVS

Question 0

At a constant total peripheral resistance, what happens to arterial and venous pressure if cardiac output increases?

Answer 0

Arterial pressure will increase

Venous pressure will fall

Question 1

At a given cardiac output, what happens to arterial and venous pressure if total peripheral resistance falls?

Answer 1

Arterial pressure will fall and venous pressure will rise

Question 2

Define stroke volume

Answer 2

Difference between end diastolic volume and end systolic volume

Question 3

Define end diastolic volume

Answer 3

Volume of blood in the ventricle at the end of diastole

Question 4

What is end systolic volume?

Answer 4

Volume of blood in the ventricle at the end of systole

Question 5

When do the ventricles stop filling?

Answer 5

Until the walls stretch enough to produce an intra-ventricular pressure equal to venous pressure

Question 6

What determines how much the heart fills in diastole?

Answer 6

The venous pressure. The higher the venous pressure, the more the heart fills.

Question 7

What is the curve for the relationship between venous pressure and ventricular volume?

Answer 7

The ventricular compliance curve

Question 8

Define pre-load

Answer 8

End diastolic stretch of the myocardium

Question 9

What is afterload?

Answer 9

The force necessary to expel blood into the arteries

Question 10

What makes the ventricles contract harder?

Answer 10

The more they stretch before contracting, so the more the heart fills. Therefore a bigger stroke volume

Question 11

What does a rise in venous pressure lead to?

Answer 11

A rise in stroke volume due to increased filling of the ventricles and harder contraction.

Question 12

Describe the curve showing the relationship between venous pressure and stoke volume at a constant afterload

Answer 12

Curve steeply increases, then slows down as it gets to the peak. Begins to curve downwards. (Looks like a tilted walking stick)

Question 13

What is contractility?

Answer 13

The stroke volume you get for a given venous pressure

Question 14

What increases the contractility?

Answer 14

Sympathetic activity

Question 15

What controls autonomic outflow?

Answer 15

Signals from baroreceptors which are located in the arch of the aorta and the carotid sinus

Question 16

Where do baroreceptors send their signals to?

Answer 16

The medulla

Question 17

If venous pressure rises, what happens to cardiac output?

Answer 17

It rises

Question 18

If arterial pressure rises, what happens to cardiac output?

Answer 18

It falls

Question 19

How does the CVS respond to eating a meal?

Answer 19

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

Question 20

Response of CVS to exercise?

Answer 20

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

Question 21

What would happen if the heart rate didn’t speed up in advance when exercising?

Answer 21

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

Question 22

Response to CVS on standing up?

Answer 22

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

Question 23

What happens when there is a haemorrhage?

Answer 23

Reduction in blood volume ➡️ reduction in venous pressure ➡️ cardiac output falls ➡️ arterial pressure falls

Question 24

What is the body’s response to bleeding?

Answer 24

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

Question 25

What is auto-transfusion?

Answer 25

When fluid from tissue moves into capillaries due to a low hydrostatic pressure

Question 26

What is blood volume controlled by?

Answer 26

The kidney

Question 27

What happens if blood volume is increased long term?

Answer 27

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