The Cardiac Pump

Question 1

What are the two events happening in the late phase 1 of the cardiac cycle?

Answer 1

1) Diastasis–the mitral valve is open but there is little flow into the ventricle 2) Atrial contraction (after P wave) occurs, contributes less than 20% of ventricle’s volume

Question 2

What occurs at phase 2 of the cardiac cycle?

Answer 2

Isovolumetric contraction (start of QRS complex in EKG)

Question 3

At what point does the mitral or tricuspid valve close?

Answer 3

When the pressure in the ventricle exceeds that of the atria

Question 4

At what point does the aortic or pulmonary valve open?

Answer 4

When the pressure within the ventricles exceeds the pressure of the artery

Question 5

What two events occur in phase 3 of the cardiac cycle?

Answer 5

1) Rapid ejection–most stroke volume ejected in this early stage 2) Decreased ejection–residual stroke volume; pressure in the aorta/pulmonary artery is actually greater but the inertia of the blood flow keeps the valve open

Question 6

What occurs in phase 4 of the cardiac cycle?

Answer 6

Isovolumetric relaxation, marked by the closure of the aortic/pulmonary valves and the continued closure of the mitral/tricuspid valves. Beginning diastole

Question 7

What is the dicrotic notch?

Answer 7

A slight increase in aortic pressure that occurs when the aortic valves close

Question 8

What happens in the early phase 1 of the cardiac cycle?

Answer 8

The drop in ventricular pressure causes the mitral/tricuspid valves to open. Most initial ventricular filling occurs at this point

Question 9

What are the two main differences between the right heart cycle and the left heart cycle?

Answer 9

1) Right heart operates under much lower pressures than the left. 2) The isovolumetric phases tend to be shorter, which manifests as a different heart sound, as the pulmonary valves close at a different point than the aortic

Question 10

How is a cardiomyocyte triggered to initiate an action potential? (i.e. what is the source of its trigger?)

Answer 10

A neighboring cardiomyocyte

Question 11

What are three structural differences between cardiac muscle and skeletal muscle?

Answer 11

1) T-tubules are more developed in cardiac tissue 2) Denser sarcoplasmic reticulum between tubules 3) Denser mitochondrial concentrations

Question 12

How is calcium released to trigger contractions in a cardiomyocyte?

Answer 12

1) Action potential opens Long acting Ca++ channels (plateau phase channels) 2) Ca++ interacts with ryanodine receptors on SR 3) Calcium released

Question 13

How is relaxation of the cardiomyocyte promoted?

Answer 13

1) Ca++ dissociates from troponin C 2) SERCA uses energy to take up Ca++ into SR 3) Na/Ca antiporters or Ca pump send Ca out of the cell

Question 14

How do skeletal and cardiac muscle differ with respect to passive stretching?

Answer 14

Cardiomyocytes tolerate passive stretching less effectively than skeletal muscle; presence of titin discourages stretching

Question 15

What is the main factor involved in active contraction?

Answer 15

The degree to which actin and myosin can overlap in a contractile apparatus

Question 16

What are the usual axes on the Frank-Starling curve?

Answer 16

X-axis is usually sarcomere length (represented by End-diastolic ventricular volume) Y-axis is usually force or tension (represented by mm Hg or stroke volume)

Question 17

What are the three variables involved in measuring cardiac function?

Answer 17

1) Preload (aka the amount of blood added to a system) 2) Afterload (aka the force that the myocardium must overcome) 3) Contractility (measure of intrinsic contractile force)

Question 18

What is the effect of changing the preload?

Answer 18

Increasing the preload will generally increase stroke volume and will keep one on the initial Frank-Starling curve. Decreasing the preload will conduct the opposite action.

Increasing preload will increase end-diastolic volume and thus increase stroke volume

Question 19

What is the effect of changing the afterload?

Answer 19

Dropping the force that a ventricle must overcome will shift the curve upwards and to the left; increasing the force that a ventricle must overcome will shift the curve down and to the right.

Increasing the afterload decreases the stroke volume

Question 20

What is the effect of changing the contractility?

Answer 20

Increasing contractility will increase the ability of the heart to contract, and thus the Frank-Starling curve will shift up and to the left; decreasing the contractility will shift it downwards and to the right.
If contractility is increased, stroke volume increases.

Question 21

What is happening at A?

Answer 21

The mitral valve closes

Question 22

What is happening at B?

Answer 22

The aortic valve opens

Question 23

What is happening at C?

Answer 23

Aortic valve closes

Question 24

What is happening at the lower left D?

Answer 24

Mitral valve opens

Question 25

What is happening at the upper middle D?

Answer 25

Ejection

Question 26

What is happening at E?

Answer 26

Isovolumetric relaxation

Question 27

What is happening at F and what is the limit that this line represents?

Answer 27

Ventricular filling
The line closely resembles the capacity of the ventricle to accept passive stretching

Question 28

What is happening at G?

Answer 28

Isovolumetric contraction

Question 29

How is ejection fraction calculated?

Answer 29

Stroke volume/End Diastolic Volume

Question 30

Between what two representative curves must a pressure-volume loop exist?

Answer 30

The active and passive capacities of cardiomyocytes to withstand stretch

Question 31

How can intrinsic contractility be represented graphically?

Answer 31

The end systolic volume-pressure relationship slope

Question 32

What are the main molecular events of beta-adrenergic activations in cardiomyoctes?

Answer 32

1) L-type Ca++ channels become phosphorylated
2) phospholamban becomes phosphorylated

3) troponin I becomes phosphorylated
4) L-type Ca++ channels interact with activated a3 units

Question 33

What are the chemical side effects of beta-adrenergic activation?

Answer 33

Phos of L channels: Increases Ca++ influx (increases contractility)
Phospholambin: Increases Ca++ reuptake (decreases duration)
Troponin I: Dissociates Ca++ from Troponin C faster (decreases duraton)
L channel/a3 interaction: increases Ca++ influx (increases contractility)