Cardiac Cycle Flashcards
What is the cardiac cycle?
The sequence of alternating contraction and relaxation of the atria and ventricles to pump blood throughout the body.
When does the cardiac cycle start and end?
It starts at the beginning of one heartbeat and ends at the beginning of another.
At what gestational week does the heart begin to contract?
The 4th gestational week.
What are the two main phases of the cardiac cycle?
Diastole (filling phase) and systole (pumping phase).
What is the function of the sinoatrial (SA) node?
It acts as the pacemaker of the heart, setting the rhythm of contraction.
Where is the SA node located?
Near the opening of the superior vena cava on the superior lateral wall of the right atrium.
What is the atrioventricular (AV) node’s primary function?
It delays impulse transmission, allowing the atria to contract before the ventricles depolarize.
Where is the AV node located?
Medial and posterior to the tricuspid valve.
What is the bundle of His?
A network of fibers that transmit electrical signals from the AV node to the ventricles.
What are Purkinje fibers?
Fibers that supply the ventricular myocardium, ensuring coordinated contraction.
What happens during atrial diastole?
The atria relax and passively fill with blood from the veins.
What happens when atrial pressure exceeds ventricular pressure?
The atrioventricular valves open, allowing blood to flow into the ventricles.
What initiates atrial systole?
An action potential from the SA node.
What is the purpose of atrial systole?
To push residual blood from the atria into the ventricles.
What happens during early ventricular diastole?
Both atrioventricular and semilunar valves are closed, and intraventricular pressure falls.
What is isovolumetric relaxation?
A phase in early ventricular diastole where no blood flows into or out of the ventricles.
What is diastasis?
The middle phase of ventricular diastole, where passive filling slows before atrial contraction.
What is the end-diastolic volume (preload)?
The total volume of blood in the ventricles at the end of diastole.
What happens during ventricular systole?
The ventricles contract and eject blood into the arteries.
What is isovolumetric contraction?
The phase in ventricular systole where pressure builds, but no blood is ejected.
When do the semilunar valves open?
When ventricular pressure exceeds arterial pressure.
What is the ejection phase?
The period during ventricular systole when blood is pushed into the arteries.
What is end-systolic volume (afterload)?
The volume of blood remaining in the ventricle after contraction (~40-50 mL).
What is stroke volume?
The amount of blood ejected from the ventricle per heartbeat.
What is ejection fraction?
The ratio of stroke volume to end-diastolic volume (~60%).
What is the Wiggers Diagram?
A diagram that illustrates pressure, volume, and electrical activity changes in the cardiac cycle.
What are the major phases of the Wiggers Diagram?
Atrial diastole, atrial systole, ventricular systole, and ventricular diastole.
What is the ‘a’ wave in atrial pressure?
Represents atrial contraction.
What is the ‘v’ wave in atrial pressure?
Represents atrial filling with blood.
What is the ‘c’ wave in atrial pressure?
Represents bulging of the AV valves into the atria during ventricular contraction.
What is an ECG?
A graphical representation of the heart’s electrical activity.
What does the P wave represent?
Atrial depolarization.
What does the QRS complex represent?
Ventricular depolarization and contraction.
What does the T wave represent?
Ventricular repolarization and relaxation.
What is the significance of the AV node delay?
It allows the atria to contract before ventricular depolarization occurs.
Which phase of the cardiac cycle is the longest?
Diastasis.
How does the SA node spread its impulse?
Through preferential conductive pathways.
What determines heart rate?
The firing rate of the SA node.
What happens if the SA node fails?
The AV node takes over, but at a slower rate.
What is the function of gap junctions?
They allow electrical impulses to spread directly between myocytes.
What is cardiac syncytium?
A network where heart cells contract almost simultaneously due to electrical connectivity.
Which valve opens first during ventricular diastole?
The atrioventricular valve.
What prevents backflow of blood into the atria?
The closure of the atrioventricular valves.
What structure connects the AV node to the ventricles?
The bundle of His.
How do Purkinje fibers aid in contraction?
They distribute electrical impulses rapidly across the ventricles.
What is the Frank-Starling law?
The heart pumps more forcefully when filled with more blood.
What is preload?
The initial stretching of the ventricles before contraction.
What is afterload?
The resistance the heart must overcome to eject blood.
What is the role of calcium in cardiac contraction?
It triggers myocyte contraction by binding to troponin.
Which ion is primarily responsible for depolarization?
Sodium (Na+).
Which ion is primarily responsible for repolarization?
Potassium (K+).
What is cardiac output?
The volume of blood pumped by the heart per minute (stroke volume × heart rate).
What is the normal resting heart rate?
About 60-100 beats per minute.
What happens to the cardiac cycle during exercise?
It shortens, increasing heart rate and cardiac output.
