Cardiac Cycle Quiz

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Questions and Answers

What occurs during the isovolumetric contraction phase?

Blood is ejected from the ventricles into the arteries.

The ventricles are contracting with constant volume. (correct)

Ventricular pressure is lower than aortic pressure.

The AV valves are open and blood fills the ventricles.

What marks the beginning of ventricular systole?

Opening of the atrioventricular (AV) valves

Increase in atrial pressure

Closure of the semilunar valves

Electrical depolarization represented by the QRS complex (correct)

What is the significance of isovolumetric relaxation in the cardiac cycle?

It allows for blood to flow back into the ventricles.

It prevents backflow into the atria during pressure changes. (correct)

It allows for the ventricles to fill with blood.

It increases the heart rate significantly.

What event follows the QRS complex in terms of ventricular pressure changes?

Ventricular pressure rises above aortic pressure immediately. Signup and view all the answers

Which of the following statements is true about the phases where ventricular volume remains constant?

Both phases occur with all valves closed. Signup and view all the answers

What causes the first heart sound (S1) during the cardiac cycle?

Closure of both AV valves Signup and view all the answers

How do isovolumetric phases contribute to the cardiac cycle?

They allow for sufficient ventricular pressure to open semilunar valves. Signup and view all the answers

What is the primary mechanical event during isovolumetric contraction?

Ventricular pressure builds with no volume change. Signup and view all the answers

What is the primary function of the pericardial sac?

To reduce friction as the heart beats Signup and view all the answers

Which feature distinguishes cardiac muscle from skeletal muscle?

Cardiac muscle contains intercalated discs Signup and view all the answers

What would likely occur if gap junctions in cardiac muscle were selectively blocked?

Isolated contractions and arrhythmias Signup and view all the answers

What is a characteristic of cardiac muscle fibers?

They have a single centrally located nucleus Signup and view all the answers

Which statement about cardiac muscle contraction is true?

The action potential spreads rapidly through electrically coupled cells Signup and view all the answers

What are desmosomes in cardiac muscle responsible for?

Anchoring muscle fibers securely together Signup and view all the answers

Which of the following describes the branching structure of cardiac muscle?

It helps the heart contract as a single unit Signup and view all the answers

Why is proper electrical communication essential in cardiac muscle?

To ensure effective pumping of blood Signup and view all the answers

What occurs during the plateau phase of the cardiac action potential?

Calcium ions enter the cell while potassium ions leave. Signup and view all the answers

What is the purpose of the plateau phase in cardiac cells?

To allow neighboring cells enough time to contract simultaneously. Signup and view all the answers

Where is the sinoatrial (SA) node located?

In the right atrium near the superior vena cava. Signup and view all the answers

What is the primary role of the Atrioventricular (AV) node?

To delay the action potential to allow for ventricular filling. Signup and view all the answers

How does the action potential spread from the SA node?

In multiple directions simultaneously: left atrium, right atrium, and AV node. Signup and view all the answers

Which structure branches from the AV node and runs along the interventricular septum?

Bundle of His. Signup and view all the answers

What is the first action potential event in the heart's conduction system?

Initiation in the SA node. Signup and view all the answers

Which ion movement restores the negative membrane potential during repolarization?

Potassium ions leave the cell. Signup and view all the answers

What is the primary function of the Bundle of His in the heart?

To spread signals to the Purkinje fibers after the AV node fires Signup and view all the answers

Why is the Sinoatrial (SA) node termed the pacemaker of the heart?

It spontaneously generates action potentials at the fastest rate. Signup and view all the answers

What would become the heart's pacemaker if the SA node ceased functioning?

The AV node Signup and view all the answers

What is the purpose of the AV nodal delay?

To let the atria fully empty their blood into the ventricles Signup and view all the answers

If both parasympathetic and sympathetic innervation to the heart is severed, what will determine the heart rate?

The intrinsic firing rate of the SA node Signup and view all the answers

Which part of the heart has the slowest intrinsic firing rate compared to other components?

Purkinje fibers Signup and view all the answers

What potential consequence arises if the ventricles contract simultaneously with the atria?

Decreased blood ejection efficiency Signup and view all the answers

How fast does the AV node typically fire compared to the SA node?

40-60 beats per minute, slower than the SA node Signup and view all the answers

What electrical event corresponds with isovolumetric contraction?

Ventricular depolarization Signup and view all the answers

Which heart sound is associated with the closure of the AV valves during isovolumetric contraction?

S1 (lub) Signup and view all the answers

What happens to ventricular volume during isovolumetric contraction?

Remains constant Signup and view all the answers

During which phase does ventricular pressure first exceed the aortic pressure, allowing blood ejection?

Ventricular ejection Signup and view all the answers

Which volume is referred to as the volume of blood remaining in the ventricles after contraction?

End-systolic volume (ESV) Signup and view all the answers

What electrical event corresponds to isovolumetric relaxation?

T wave Signup and view all the answers

During which phase does blood flow passively from the atria into the ventricles?

Passive ventricular filling Signup and view all the answers

What is the only time during the cardiac cycle that ventricular volume is not changing?

Both B and C Signup and view all the answers

What occurs when left ventricular pressure exceeds aortic pressure?

Opening of the Semilunar valves Signup and view all the answers

During isovolumetric contraction, which pressure is higher in the ventricles compared to the atria?

Ventricular pressure Signup and view all the answers

What pressure must the left ventricle exceed to initiate the ejection phase?

Aortic pressure Signup and view all the answers

What mechanical event occurs during the second heart sound (S2)?

Semilunar valves close Signup and view all the answers

If left ventricular pressure is at 95 mmHg, which condition can this indicate?

End of isovolumetric contraction Signup and view all the answers

During what phase does aortic pressure exceed ventricular pressure?

Isovolumetric relaxation Signup and view all the answers

What electrical event is associated with ventricular repolarization in relation to the heart sounds?

Peak of the T wave Signup and view all the answers

If a patient's second heart sound is muffled, which valve is most likely affected?

Aortic valve Signup and view all the answers

What is the main purpose of the epicardium within the pericardial sac?

To reduce friction during heartbeats Signup and view all the answers

Which feature of cardiac muscle allows for rapid electrical communication between cells?

Intercalated discs Signup and view all the answers

How does the blockade of gap junctions in cardiac muscle cells affect heart function?

It disrupts the synchronized contraction of the heart Signup and view all the answers

What structural feature of cardiac muscle provides strong mechanical attachments between cells?

Desmosomes Signup and view all the answers

Which characteristic of cardiac muscle distinguishes it from skeletal muscle?

Branches forming interconnections Signup and view all the answers

What could result from a failure of cardiac muscle to operate as a single unit?

Disrupted blood flow and potential arrhythmias Signup and view all the answers

What role do gap junctions serve within the cardiac muscle cells?

To facilitate rapid electrical signaling between cells Signup and view all the answers

Which outcome is least likely to occur if the pericardial cavity is compromised?

Improvement of cardiac output Signup and view all the answers

What does the P wave on an EKG represent?

Atrial depolarization Signup and view all the answers

Which interval on an EKG represents the time for an impulse to travel from the SA node to the AV node?

PR Interval Signup and view all the answers

What does the T wave indicate in a cardiac cycle?

Ventricular repolarization Signup and view all the answers

During which part of the cardiac cycle does the ST segment occur?

Ventricular systole Signup and view all the answers

What happens to the distance between R waves on an EKG as the heart rate increases?

It decreases Signup and view all the answers

What is the significance of the AV nodal delay in an EKG reading?

It allows for ventricular filling Signup and view all the answers

Which electrical event is represented by the QRS complex on an EKG?

Ventricular depolarization Signup and view all the answers

What does the TP interval on an EKG signify?

Diastolic period for filling Signup and view all the answers

What is the primary purpose of the isovolumetric contraction phase in the cardiac cycle?

To increase ventricular pressure to open the semilunar valves Signup and view all the answers

What occurs immediately after the closure of the AV valves?

Isovolumetric contraction takes place Signup and view all the answers

Which event is directly associated with the QRS complex on an electrocardiogram?

Ventricular depolarization begins Signup and view all the answers

During which cardiac cycle phase is the pressure in the ventricles higher than that in the atria?

Isovolumetric contraction Signup and view all the answers

What physical change occurs during isovolumetric relaxation?

Ventricular pressure decreases with constant volume Signup and view all the answers

What is a key consequence of the phases of isovolumetric contraction and relaxation?

Establishing a unidirectional blood flow through the heart Signup and view all the answers

Which heart sound is associated with the closure of the semilunar valves?

S2 Signup and view all the answers

What happens to ventricular volume during the isovolumetric phases of the cardiac cycle?

It remains constant Signup and view all the answers

Which ion primarily contributes to the slow depolarization phase in autorhythmic cells?

Sodium ions (Na+) Signup and view all the answers

What is the role of L-type calcium channels in the action potential of autorhythmic cells?

They cause rapid depolarization. Signup and view all the answers

Which phase immediately follows the rapid depolarization in cardiac muscle cells?

Phase 1: Early Repolarization Signup and view all the answers

What occurs during the repolarization phase of autorhythmic cells?

Potassium ions leave the cell, restoring negativity. Signup and view all the answers

What differentiates the action potential in cardiac muscle cells from that in autorhythmic cells?

Autorhythmic cells have no resting membrane potential. Signup and view all the answers

Which statement best describes the characteristics of pacemaker potential in autorhythmic cardiac cells?

It is a gradual depolarization leading to action potential generation. Signup and view all the answers

What is the significance of transient calcium channels in the action potential of autorhythmic cells?

They allow a small influx of calcium to reach the threshold. Signup and view all the answers

What defines the 'plateau phase' in cardiac muscle cells?

An extended period of depolarization due to calcium influx. Signup and view all the answers

Study Notes

Isovolumetric Contraction

Ventricular depolarization (QRS complex)
Ventricles contract, AV valves close (S1 sound)
No blood ejected; pressure not exceeding aortic or pulmonary artery pressure
All valves closed
Ventricular volume remains constant

Ventricular Ejection

Ventricular depolarization continues; repolarization begins
Ventricular pressure exceeds aortic and pulmonary artery pressure
Aortic and pulmonary valves open; blood ejected
Ventricular volume decreases (stroke volume)
End-systolic volume remains

Isovolumetric Relaxation

Ventricular repolarization (T wave)
Ventricles relax, pressure falls below aortic and pulmonary artery pressure
Aortic and pulmonary valves close (S2 sound)
No blood enters ventricles
All valves closed
Ventricular volume remains constant

Passive Ventricular Filling

No major electrical activity (TP interval)
Atrial pressure exceeds ventricular pressure; AV valves open
Blood flows passively from atria to ventricles
Ventricular volume increases (end-diastolic volume)

Ventricular Volume Changes

Ventricular volume only remains constant during isovolumetric contraction and relaxation phases

Isovolumetric Contraction Details

Occurs after atrial contraction and AV valve closure
Ventricles contract; pressure rises
Aortic and pulmonary valves remain closed due to lower ventricular pressure
All valves closed; no blood enters or leaves ventricles
Constant ventricular volume

Isovolumetric Relaxation Details

Occurs after ventricular ejection and semilunar valve closure
Ventricles relax; pressure decreases
AV valves remain closed due to higher ventricular pressure
All valves closed; no blood enters or leaves ventricles
Constant ventricular volume

Importance of Isovolumetric Phases

Pressure Build-up: Isovolumetric contraction allows pressure build-up to open semilunar valves and eject blood.
Prevention of Backflow: Both phases prevent blood from flowing back into atria or ventricles, maintaining unidirectional blood flow.

QRS Complex Events

Ventricular depolarization (electrical signal for contraction) at the start of systole
Left ventricular pressure increases, exceeding atrial pressure, leading to AV valve closure
First heart sound (S1) heard due to AV valve closure
Isovolumetric contraction begins: Ventricles contract, building pressure, but all valves remain closed

Pericardium

Sac surrounding the heart with two layers:
- Epicardium (inner layer against the heart)
- Pericardium (outer fibrous layer)
Fluid between layers reduces friction during heartbeats, preventing damage

Cardiac Muscle

Not under voluntary control
Striated (linear muscle lines) due to intracellular protein organization for contraction
Single central nucleus
Branched fibers, forming a network for coordinated contraction
Intercalated discs connect cardiac cells
- Gap junctions: Allow rapid electrical communication between cells
- Desmosomes: Protein anchors for strong mechanical attachment

Consequences of Gap Junction Blockade

Impaired action potential movement throughout the heart
Isolated contractions, resembling defibrillation (quivering)
Disrupted synchronization; inefficient blood pumping
Arrhythmias due to lack of coordinated electrical signals
Reduced cardiac output

Cardiac Action Potential Phases

Phase 0: Depolarization
- Sodium channels open; sodium ions (Na+) rush into the cell
- Rapid increase in membrane potential
Phase 2: Plateau Phase
- Calcium channels open; calcium ions (Ca++) enter the cell
- Potassium channels open; potassium ions (K+) leave the cell
- Plateau maintains sustained depolarization
- Allows time for action potential to spread throughout the heart
Phase 3: Repolarization
- Calcium channels close; calcium influx stops
- Potassium channels fully open; potassium ions continue leaving the cell, restoring negative membrane potential

Autorhythmic Cell Locations

Sinoatrial (SA) Node: In right atrium near superior vena cava, acts as heart's pacemaker
Atrioventricular (AV) Node: Between atria and ventricles, near interatrial septum
Bundle of His: Arises from AV node, branches into left and right bundle branches along the interventricular septum
Purkinje Fibers: Extend from bundle branches, spread throughout ventricular muscle

Action Potential Flow Direction

Starts in SA node, spreads across atria causing atrial contraction
- To left atrium via interatrial pathway
- To right atrium and atrial mass
- To AV node via intranodal pathway
AV node delay (100 milliseconds) allows for complete atrial contraction and ventricular filling
Signals travel through Bundle of His, then to bundle branches, and finally Purkinje fibers
Ventricles contract nearly simultaneously

SA Node as Pacemaker

SA node spontaneously generates action potentials at the fastest rate (70-80 bpm)
- The SA node has the fastest firing rate
- AV node (40-60 bpm) and Bundle of His/Purkinje fibers (20-40 bpm) are slower

AV Node Takeover

If SA node fails, AV node becomes the pacemaker due to its second fastest rate

Purpose of AV Nodal Delay

Allows atria to contract and fill ventricles before ventricular contraction
Maximizes blood volume in ventricles before ejection
Optimizes blood pumping efficiency

Heart Rate Without Nervous Innervation

Heart rate would be determined by the SA node's intrinsic firing rate (70-80 bpm)
Nervous system input modulates the SA node's inherent rate

Cardiac Cycle Phases

Isovolumetric Contraction
- Occurs after atrial contraction and closure of AV valves (S1 sound).
- Ventricles contract, pressure rises but aortic/pulmonary valves remain closed.
- All valves closed, no blood flow, constant ventricular volume.
Isovolumetric Relaxation
- Occurs after ventricular ejection and closure of semilunar valves (S2 sound).
- Ventricles relax, pressure drops, but AV valves remain closed.
- All valves closed, no blood flow, constant ventricular volume.

Importance of Phases

Pressure Build-up: Isovolumetric contraction allows ventricles to build enough pressure to open semilunar valves and eject blood.
Prevention of Backflow: Both phases prevent blood backflow, maintaining unidirectional blood flow through the heart.

Electrical and Mechanical Events during QRS Complex

QRS Complex: Represents ventricular depolarization, beginning of ventricular systole.
Ventricular Pressure Increase: Left ventricular pressure exceeds atrial pressure causing AV valves to close (S1 sound).
Isovolumetric Contraction: Ventricles contract, building pressure but all valves remain closed.

Pericardium

Structure: Surrounds the heart, with two layers:
- Epicardium(inner against the heart).
- Pericardium (outer fibrous layer).
- Pericardial Cavity: Space between layers filled with fluid.
Function: Reduces friction during heartbeats, preventing damage from rubbing.

Cardiac Muscle Features

Involuntary Control: Not under conscious control.
Striated: Linear muscle lines along muscle cells (due to organized intracellular proteins).
Single Central Nucleus: Most cells have one centrally located nucleus.
Branching Fibers: Branched fibers create a network for synchronized contraction.
Intercalated Discs: Junction points between cells.
- Gap Junctions: Rapid electrical communication between cells (electrically coupled).
- Desmosomes: Strong mechanical anchoring between cells.

Gap Junction Blockade Consequences

Disrupted Synchronization: Impaired coordinated contraction of the heart as a unit.
Arrhythmias: Irregular heartbeats due to lack of synchronized electrical signals.
Inefficient Pumping: Reduced cardiac output and potentially leading to cardiac arrest.

Autorhythmic Cell Action Potential

Spontaneous Action Potential Generation: Initiate and coordinate heartbeat.
Four Phases:
- Phase 4 (No Resting State): Sodium leak channels contribute to a negative membrane potential (-60mV).
- Phase 2 (Slow Depolarization): Leak sodium channels and transient calcium channels (T-type) gradually increase membrane potential.
- Phase 3 (Rapid Depolarization): Long-lasting calcium channels (L-type) open, rapid influx of calcium ions (Ca++) leading to sharp rise in membrane potential.
- Phase 4 (Repolarization): Potassium channels open, potassium ions (K+) leave the cell, restoring negative potential.

Cardiac Muscle Cell Action Potential

Stimulation Required: Need external stimulation to trigger action potential.
Plateau Phase: Distinguishes it from autorhythmic cells.
No Hyperpolarization Phase: Membrane potential returns directly to resting state.
Four Phases:
- Phase 4 (Resting Membrane Potential): Stable negative membrane potential at rest.
- Phase 0 (Rapid Depolarization): Sodium channels open, rapid influx of sodium ions (Na+) leading to depolarization.
- Phase 1 (Early Repolarization): Sodium channels close, slight decrease in membrane potential.
- Phase 2 (Plateau Phase): Calcium channels open, prolonging depolarization, followed by repolarization (due to potassium channels opening).

EKG Waveform Correlation

P Wave: Atrial depolarization (SA node action potential).
PR Interval: Time for electrical impulse travel from SA node to AV node (including AV nodal delay).
QRS Complex: Ventricular depolarization, causing ventricular contraction.
ST Segment: Time of sustained ventricular depolarization and contraction (plateau phase of action potential).
T Wave: Ventricular repolarization returning the muscle to resting state.
TP Interval: Diastole, both atria and ventricles filling with blood.

Heart Rate and EKG Waveforms

Decreased Waveform Distance: Distance between any two waveforms (e.g., R to R) decreases with increased heart rate.

Cardiac Cycle Events Summary

Atrial Systole (P Wave):
- Electrical Event: Atrial depolarization.
- Mechanical Event: Atrial contraction, pushing blood into ventricles. AV valves open, blood flows from atria to ventricles.
- Ventricular Volume: Increases as they fill, reaching EDV (End Diastolic Volume).
Ventricular Systole (QRS Complex):
- Electrical Event: Ventricular depolarization.
- Mechanical Event: Ventricular contraction (ventricular systole) forcing blood into aorta/pulmonary artery.

Pressure Differences during Isovolumetric Contraction

Ventricles vs. Atria: Ventricular pressure greater than atrial pressure (forces AV valves closed).
Ventricles vs. Arteries: Arterial pressure higher than ventricular pressure (ventricles still building pressure).

Transition from Isovolumetric Contraction to Ejection

Ventricular Pressure Exceeding Aortic Pressure: Aortic valve opens, ejecting blood.

Second Heart Sound (S2)

Ventricles Relaxing: Ventricular repolarization (middle of T wave on EKG).
Aortic Pressure Exceeds Ventricular Pressure: Semilunar valves close (aortic/pulmonary) to prevent backflow.
Dicrotic Notch: Pressure wave traveling back up aorta from valve closure, creating a small bump in aortic pressure.

Abnormal Second Heart Sound

Aortic Valve Problem: Muffled or whistling sound, likely indicates an issue with the aortic valve.

Hypertension and Left Ventricular Pressure

Left Ventricular Pressure needs to reach at least 95mmHg to overcome the diastolic pressure in the patient with hypertension.

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Description

Test your knowledge on the cardiac cycle phases, including isovolumetric contraction, ventricular ejection, isovolumetric relaxation, and passive ventricular filling. Understand the key concepts and physiological changes that occur during each phase of the heart's pumping action.