CVS - Control Of Cardiac Output

Question 1

What is afterload?

Answer 1

The load that the heart must eject blood against (roughly equivalent to aortic pressure)

Question 2

What is preload?

Answer 2

Amount the ventricles are stretched in diastole - related to end diastolic volume

Question 3

What is total peripheral resistance?

Answer 3

Aka systemic vascular resistance, this is the resistance to blood flow offered by all the systemic vasculature.

Question 4

Why does contraction of the arterioles cause pressure on the arterial side to rise, while pressure on the venous side falls?

Answer 4

Constriction causes the artery to narrow. This means that less blood can get through, so pressure rises on the arterial side (before the blockage) and falls on the venous side (after the blockage).

Question 5

What happens to arterial and venous pressure if total peripheral resistance FALLS and cardiac output is UNCHANGED?

Answer 5

Arterial pressure will fall and venous pressure will increase.

Question 6

What happens to arterial and venous pressure if total peripheral resistance INCREASES and cardiac output is UNCHANGED?

Answer 6

Atrial pressure increases, venous pressure falls

Question 7

What happens to arterial and venous pressure if total peripheral resistance is UNCHANGED and cardiac output INCREASES?

Answer 7

Arterial pressure will increase and venous pressure will fall

Question 8

What happens to arterial and venous pressure if total peripheral resistance is UNCHANGED and cardiac output DECREASES?

Answer 8

Arterial pressure will fall and venous pressure will rise

Question 9

What is the result of arterioles and pre-capillary sphincters dilating?

Answer 9

Peripheral resistance falls

Question 10

Stroke volume x heart rate = ?

Answer 10

Cardiac output

Question 11

End diastolic volume - end systolic volume = ?

Answer 11

Stroke volume

Question 12

How can stroke volume be increased?

Answer 12

Increase end diastolic volume or decrease end systolic volume.

Question 13

What is the Ventricular Compliance Curve used to illustrate?

Answer 13

Shows the relationship between venous pressure and heart filling.

• in state of decreased compliance, LV pressure increases while LV volume does not increase much
• in state of increased compliance, LV volume increases a lot but pressure does not increase

Question 14

What is the Frank-Starling Law of the Heart?

Answer 14

The idea that the more the heart fills, the harder it contracts, which increases the stroke volume. The sarcomeres can be stretched to the optimum length, allowing better contraction

Question 15

Is increased stroke volume with increased filling of the heart an intrinsic or extrinsic control mechanism?

Answer 15

Intrinsic

Question 16

True or false - Starling’s law of the heart ensures that both sides of the heart are balanced?

Answer 16

True - they must both maintain the same output.

Question 17

What is contractility?

Answer 17

The force of contraction for a given fibre length

Question 18

Give some examples of extrinsic factors which can increase contractility

Answer 18

Sympathetic stimulation and circulating adrenaline

Question 19

Which factors determine cardiac output?

Answer 19

• how hard the ventricle contracts (determined by end diastolic volume and contractility)
• how hard it is to eject blood (determined by aortic impedance)