Session 6 - Control Of The CVS

Question 1

What will happen to arterial and venous pressures if CO rises at a constant TPR?

Answer 1

Arterial pressure will rise

Venous pressure will fall

Question 2

Define Diastolic Volume

Answer 2

The volume of blood in the ventricle at the end of diastole

Question 3

Define Systolic Volume

Answer 3

The volume of blood in the ventricle at the end of systole

Question 4

Define Stroke Volume

Answer 4

The difference between end diastolic volume and end systolic volume

Question 5

State and explain the relationship between venous pressure and end diastolic volume

Answer 5

• 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

Question 6

When plotted on a graph what is the relationship between the end is stolid volume and the venous pressure known as?

Answer 6

The ventricular compliance curve

Question 7

Define “Pre-Load” and what is it determined by?

Answer 7

The end-diastolic stretch on the myocardium

Determined by venous pressure

Question 8

Define “After-Load”

Answer 8

The force necessary to expel blood into the arteries

Question 9

What is Starling’s Law?

Answer 9

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

Question 10

What is the relationship between venous pressure and stroke volume?

Answer 10

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

Question 11

What is contractility?

Answer 11

The gradient of Starling’s Curve. (Graph of venous pressure against stroke volume)

Question 12

What is contractility increased by?

Answer 12

Sympathetic activity

Question 13

How does the brain detect changes in blood pressure?

Answer 13

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

Question 14

What will happen to CO if venous pressure falls?

Answer 14

Co will fall

Question 15

What will happen to CO if arterial pressure falls?

Answer 15

CO will rise

Question 16

What is the response of the CVS after a meal?

Answer 16

• 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

Question 17

How could pulmonary Oedemma be a risk during exercise?

Answer 17

• 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

Question 18

How is a Pulmonary Oedemma prevented in response to exercise?

Answer 18

• Heart Rate increases
• when the venous pressure increases HR already is high
• Stroke volume kept down but CO increased

Question 19

How does the CVS respond to standing up?

Answer 19

• 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

Question 20

How does the CVS respond to Haemorrhage?

Answer 20

• 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

Question 21

How does the CVS respond to a long term increase in blood volume?

Answer 21

• 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

Question 22

What will happen to arterial and venous pressures if TPR falls at a constant CO?

Answer 22

Arterial pressure will decrease

Venous pressure will increase