Cardiac Output

Question 1

What occurs when the left (and right) ventricle is relaxed? What is this period called?

Answer 1

When relaxed, the left (and right) ventricle is filling with blood - this period is called diastole

Question 2

What do the atria mainly act as?

Answer 2

Reservoirs - store blood for entry into the ventricles and subsequent blood pumping

Question 3

Which circulation does the left side of the heart supply blood? Which circulation does the right side supply?

Answer 3

The left side of the heart supplies blood to systemic circulation - the right side of the heart supplies blood to the pulmonary circulation (the lungs)

Question 4

Define the term systole.

Answer 4

Systole relates to the contraction of the ventricles, where blood is forced from the heart due to increases in intraventricular pressure, entering pulmonary (the lungs) and systemic circulation (the aorta)

Question 5

What is myocardium?

Answer 5

The muscular tissue responsible for the contraction responsible for the contraction of the heart

Question 6

What is regarded as the pacemaker of the heart? Where is it located?

Answer 6

The sinoatrial node - this is located in the right atrium

Question 7

What causes the atria to contract?

Answer 7

Direct innervation from the sinoatrial node

Question 8

What structure is responsible for delaying the electrical stimulus leading to ventricular contraction? Why does this delay occur?

Answer 8

The atrio-ventricular node - this ensures the ventricle pumps inferiorly from the apex of the heart upwards

Question 9

Define afterload.

Answer 9

The load that the heart must eject against

Question 10

What is after load roughly equivalent to?

Answer 10

Aortic pressure

Question 11

Define preload.

Answer 11

The load that causes the ventricles to stretch of fill in diastole

Question 12

Mathematically, define stroke volume.

Answer 12

End diastolic volume - end systolic volume = stroke volume

Question 13

What will vasoconstriction of an arteriole do the the blood pressure either side of the constriction?

Answer 13

The BP preceding the constriction will increase, while the BP proceeding the constriction will decrease

Question 14

What does the FRnk-Starling Law of the heart suggest?

Answer 14

The more the fibres of the heart are stretched (upon filling) the greater the contraction of the heart

Question 15

How does total peripheral resistance influence cardiac output?

Answer 15

The greater the TPR the lower the venous pressure and the lower CO
The lower the TPR the greater the venous return and the greater the CO

Question 16

How does venous pressure influence cardiac output?

Answer 16

The greater the venous pressure the greater the preload, and the greater the stroke volume - therefore CO is increased
The lower the venous pressure the lower the preload, and the lower the stroke volume - therefore CO is decreased

Question 17

Define contractility.

Answer 17

The force of contraction for a given fibre length

Question 18

What is aortic impedance?

Answer 18

The pressure that the heart has to pump against (the afterload)

Question 19

Describe how standing up influences cardiac output.

Answer 19

Standing up means blood pools in the legs due to gravity - there is reduced venous return, leading to decreased cardiac output, and decreased total peripheral resistance - this is called postural hypotension

Question 20

What mechanism is used to counter-act postural hypotension?

Answer 20

The baroreceptor reflex

Question 21

What does the Frank-Starling Law of the heart suggest about contractility?

Answer 21

The greater the contractility, the greater the force of contraction

Question 22

How does cardiac output influence the venous pressure?

Answer 22

The greater the CO, the lower the venous pressure

The lower the CO, the greater the venous pressure

Question 23

State the 2 factors that determine how much blood the heart pumps in systole?

Answer 23

• how hard the heart contracts - contractility, related to the filling (preload)
• how hard it is to eject blood - the arterial pressure, related to total peripheral resistance (afterload)

Question 24

Describe how exercise affects cardiac output.

Answer 24

An increase in exercise will reduce the total peripheral resistance to supply blood to tissue, increasing the amount of Venus return - this I’ll ac to increase preload and increase stroke volume, leading to an increased CO

Question 25

Define diastole.

Answer 25

The filling of the heart, where the ventricles are relaxed