The Cardiac Pump Flashcards
What are the two events happening in the late phase 1 of the cardiac cycle?
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
What occurs at phase 2 of the cardiac cycle?
Isovolumetric contraction (start of QRS complex in EKG)
At what point does the mitral or tricuspid valve close?
When the pressure in the ventricle exceeds that of the atria
At what point does the aortic or pulmonary valve open?
When the pressure within the ventricles exceeds the pressure of the artery
What two events occur in phase 3 of the cardiac cycle?
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
What occurs in phase 4 of the cardiac cycle?
Isovolumetric relaxation, marked by the closure of the aortic/pulmonary valves and the continued closure of the mitral/tricuspid valves. Beginning diastole
What is the dicrotic notch?
A slight increase in aortic pressure that occurs when the aortic valves close
What happens in the early phase 1 of the cardiac cycle?
The drop in ventricular pressure causes the mitral/tricuspid valves to open. Most initial ventricular filling occurs at this point
What are the two main differences between the right heart cycle and the left heart cycle?
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
How is a cardiomyocyte triggered to initiate an action potential? (i.e. what is the source of its trigger?)
A neighboring cardiomyocyte
What are three structural differences between cardiac muscle and skeletal muscle?
1) T-tubules are more developed in cardiac tissue 2) Denser sarcoplasmic reticulum between tubules 3) Denser mitochondrial concentrations
How is calcium released to trigger contractions in a cardiomyocyte?
1) Action potential opens Long acting Ca++ channels (plateau phase channels) 2) Ca++ interacts with ryanodine receptors on SR 3) Calcium released
How is relaxation of the cardiomyocyte promoted?
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
How do skeletal and cardiac muscle differ with respect to passive stretching?
Cardiomyocytes tolerate passive stretching less effectively than skeletal muscle; presence of titin discourages stretching
What is the main factor involved in active contraction?
The degree to which actin and myosin can overlap in a contractile apparatus
What are the usual axes on the Frank-Starling curve?
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)
What are the three variables involved in measuring cardiac function?
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)
What is the effect of changing the preload?
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
What is the effect of changing the afterload?
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
What is the effect of changing the contractility?
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.
What is happening at A?
The mitral valve closes
What is happening at B?
The aortic valve opens
What is happening at C?
Aortic valve closes
What is happening at the lower left D?
Mitral valve opens
What is happening at the upper middle D?
Ejection
What is happening at E?
Isovolumetric relaxation
What is happening at F and what is the limit that this line represents?
Ventricular filling
The line closely resembles the capacity of the ventricle to accept passive stretching
What is happening at G?
Isovolumetric contraction
How is ejection fraction calculated?
Stroke volume/End Diastolic Volume
Between what two representative curves must a pressure-volume loop exist?
The active and passive capacities of cardiomyocytes to withstand stretch
How can intrinsic contractility be represented graphically?
The end systolic volume-pressure relationship slope
What are the main molecular events of beta-adrenergic activations in cardiomyoctes?
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
What are the chemical side effects of beta-adrenergic activation?
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)
