Cardiac Muscle and Electrical Activity
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Cardiac Muscle and Electrical Activity

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Questions and Answers

What role do gap junctions play in cardiac muscle cells?

  • They allow for slow communication between cells.
  • They prevent the coordination of heartbeats.
  • They enable rapid communication and synchronization. (correct)
  • They block electrical signals between muscle fibers.

    • Which ion is primarily responsible for rapid depolarization during Phase 0 of the cardiac action potential?

  • Cl-
  • Ca2+
  • Na+ (correct)
  • K+

    • During which phase of the cardiac action potential does the plateau occur, maintained by Ca2+ influx?

  • Phase 2 (correct)
  • Phase 3
  • Phase 4
  • Phase 1

    • What is the primary function of the Bundle of His in the conduction system?

    <p>It conducts impulses to the ventricles.</p> Signup and view all the answers

    What is the role of calcium in cardiac muscle contraction?

    <p>It initiates contraction and regulates strength.</p> Signup and view all the answers

    What distinguishes nodal cells from contractile cells in the heart?

    <p>Nodal cells generate spontaneous action potentials.</p> Signup and view all the answers

    How does a parallel arrangement of blood vessels differ from a series arrangement in circulation?

    <p>Parallel arrangement allows equal blood quality to tissues.</p> Signup and view all the answers

    Which ion channels are primarily involved in the rapid repolarization phase of the cardiac action potential?

    <p>K+ channels</p> Signup and view all the answers

    What is the role of the absolute refractory period in cardiac muscle?

    <p>It prevents tetanic contractions in cardiac muscle.</p> Signup and view all the answers

    What characterizes the diastolic phase of the cardiac cycle?

    <p>Blood flows passively from the atria to the ventricles.</p> Signup and view all the answers

    Which equation correctly defines cardiac output?

    <p>CO = Heart Rate (HR) x Stroke Volume (SV)</p> Signup and view all the answers

    In which phase of the cardiac cycle do the ventricles contract with all valves closed?

    <p>Isovolumetric Contraction</p> Signup and view all the answers

    What is the physiological significance of refractory periods in the heart?

    <p>They allow time for the heart to refill with blood.</p> Signup and view all the answers

    During which part of the cardiac cycle does the stroke volume get calculated?

    <p>At the end of ventricular filling</p> Signup and view all the answers

    What happens during the relative refractory period?

    <p>Some Na+ channels recover, allowing for new action potentials.</p> Signup and view all the answers

    Which blood vessel sequence correctly describes the flow of blood?

    <p>Arteries, arterioles, capillaries, venules, veins.</p> Signup and view all the answers

    What is the primary effect of sympathetic activation on the heart?

    <p>Increases heart rate and contractility</p> Signup and view all the answers

    Which receptor type is primarily targeted by the parasympathetic nervous system in cardiac regulation?

    <p>Muscarinic acetylcholine receptors</p> Signup and view all the answers

    In which phase of the cardiac action potential does calcium entry significantly influence contraction?

    <p>Phase 2 - Plateau phase</p> Signup and view all the answers

    Which characteristics are common in cardiac muscle cells compared to skeletal muscle cells?

    <p>Presence of T-tubules and troponin</p> Signup and view all the answers

    What is the role of gap junctions in cardiac muscle tissue?

    <p>Allow for rapid communication and coordinated contraction</p> Signup and view all the answers

    What is predominantly regulated by the changes in blood vessel radius in the cardiovascular system?

    <p>Vascular resistance</p> Signup and view all the answers

    How do β1-adrenergic receptors affect the heart when activated?

    <p>Increase heart rate and contractility</p> Signup and view all the answers

    What is the primary function of the SA node in the conduction pathway of the heart?

    <p>Serve as the heart's primary pacemaker</p> Signup and view all the answers

    Which layer is responsible for the protective function of the heart?

    <p>Epicardium</p> Signup and view all the answers

    Which type of blood vessel has the greatest impact on resistance according to Ohm's Law?

    <p>Arteries</p> Signup and view all the answers

    What is the primary reason for the thicker myocardium of the left ventricle compared to the right ventricle?

    <p>To generate higher pressure for systemic circulation</p> Signup and view all the answers

    Which statement accurately reflects the significance of vessel arrangement in the vascular system?

    <p>Parallel arrangement allows for uniform blood quality to tissues</p> Signup and view all the answers

    What is the primary component of blood by volume, and what percentage does it represent?

    <p>Plasma, 55-58%</p> Signup and view all the answers

    How do the pulmonary and systemic circuits differ in their arrangement?

    <p>Pulmonary is arranged in series while systemic is in parallel</p> Signup and view all the answers

    Which function is a primary role of the cardiovascular system in relation to homeostasis?

    <p>Delivering nutrients and removing waste products from cells</p> Signup and view all the answers

    What is the primary purpose of the AV node in the conduction system?

    <p>To delay the impulse for effective timing</p> Signup and view all the answers

    Which statement accurately describes the role of L-type calcium channels during cardiac action potential?

    <p>They are responsible for the plateau phase during phase 2.</p> Signup and view all the answers

    What differentiates conducting cells from contractile cells in the heart?

    <p>Conducting cells exhibit pacemaker potentials.</p> Signup and view all the answers

    What mechanism is central to excitation-contraction coupling in cardiac muscle?

    <p>Calcium-induced calcium release (CICR)</p> Signup and view all the answers

    How does the role of the Purkinje fibers contribute to heart function?

    <p>They ensure swift distribution of the impulse throughout the ventricles.</p> Signup and view all the answers

    What ion is primarily responsible for the initiation of muscle contraction in cardiac cells?

    <p>Calcium (Ca2+)</p> Signup and view all the answers

    In the cardiac action potential, what characterizes Phase 3?

    <p>Rapid repolarization from K+ efflux and Ca2+ channel closure</p> Signup and view all the answers

    What advantage does a parallel vascular arrangement provide?

    <p>Ensures all tissues receive the same quality of blood</p> Signup and view all the answers

    Which of the following best describes the role of small changes in vessel radius?

    <p>They significantly alter resistance and blood flow.</p> Signup and view all the answers

    What is the main function of atrioventricular valves in the heart?

    <p>Ensuring one-way blood flow from atria to ventricles.</p> Signup and view all the answers

    Which aspect of the cardiovascular system does Ohm's Law primarily relate to?

    <p>Flow, pressure difference, and resistance.</p> Signup and view all the answers

    How do gap junctions contribute to cardiac muscle function?

    <p>They facilitate rapid electrical signaling and contraction coordination.</p> Signup and view all the answers

    What is a primary characteristic of cardiac muscle cells compared to skeletal muscle cells?

    <p>They exhibit branching ends for interconnection.</p> Signup and view all the answers

    Which receptor types are essential for therapeutic interventions in cardiovascular diseases?

    <p>Adrenergic receptors.</p> Signup and view all the answers

    In temperature regulation, which role is primarily served by blood circulation?

    <p>Heat distribution and dissipation.</p> Signup and view all the answers

    What is the primary layer of the heart that consists of cardiac muscle?

    <p>Myocardium.</p> Signup and view all the answers

    What distinguishes cardiac muscle from smooth muscle in terms of electrical activity?

    <p>Cardiac muscle has pacemaker cells that regulate rhythm.</p> Signup and view all the answers

    What is the primary pacemaker of the heart responsible for initiating the conduction pathway?

    <p>SA node.</p> Signup and view all the answers

    What is the primary role of the absolute refractory period in cardiac muscle physiology?

    <p>To prevent new action potentials and ensure the heart refills with blood</p> Signup and view all the answers

    During which phase of the cardiac cycle is blood actively ejected into the arteries?

    <p>Ejection</p> Signup and view all the answers

    Which of the following correctly describes the stroke volume?

    <p>Volume of blood ejected from each ventricle per beat</p> Signup and view all the answers

    What is the significance of the relative refractory period?

    <p>It allows some Na+ channels to recover, enabling potential for new action potentials</p> Signup and view all the answers

    What proportion of the cardiac cycle is occupied by diastole?

    <p>2/3</p> Signup and view all the answers

    Which formula correctly calculates cardiac output?

    <p>CO = Stroke Volume x Heart Rate</p> Signup and view all the answers

    What characterizes the isovolumetric relaxation phase?

    <p>All heart valves are closed, and pressure decreases in ventricles</p> Signup and view all the answers

    How does a parallel arrangement of blood vessels affect resistance?

    <p>Decreases total resistance, enhancing blood flow</p> Signup and view all the answers

    What characterizes Heart Failure with Preserved Ejection Fraction (HFpEF)?

    <p>A stiff ventricle that struggles to relax</p> Signup and view all the answers

    Which factor does NOT influence cardiac output?

    <p>Temperature of the body</p> Signup and view all the answers

    At rest, which input primarily affects heart rate?

    <p>Parasympathetic input dominating</p> Signup and view all the answers

    What is the typical range of ejection fraction (EF) values that signify a healthy heart?

    <p>55-70%</p> Signup and view all the answers

    Which neurotransmitter supports the effects of norepinephrine in heart function?

    <p>Epinephrine</p> Signup and view all the answers

    What happens to parasympathetic input during increased physical activity?

    <p>It significantly decreases, allowing heart rate to rise</p> Signup and view all the answers

    Which condition indicates systolic dysfunction in heart failure?

    <p>Heart Failure with Reduced Ejection Fraction (HFrEF)</p> Signup and view all the answers

    What is a common effect of sympathetic activation on heart rate?

    <p>Increases heart rate and contraction strength</p> Signup and view all the answers

    What does the elevation of the S--T segment indicate in a patient?

    <p>Acute myocardial infarction</p> Signup and view all the answers

    Which phase of the cardiac action potential corresponds to ventricular depolarization?

    <p>Phase 0</p> Signup and view all the answers

    What significant electrical activity is represented by a lengthened Q--T interval?

    <p>Ventricular repolarization delay</p> Signup and view all the answers

    What effect does myocardial ischemia have on the S--T segment?

    <p>Depression below the baseline</p> Signup and view all the answers

    During which segment of an ECG does atrial systole occur?

    <p>P wave</p> Signup and view all the answers

    What primarily happens at the AV node that affects atrial and ventricular contraction timing?

    <p>Prolonging conduction time</p> Signup and view all the answers

    How does the conduction pathway influence the timing of atrial and ventricular contractions?

    <p>By allowing atrial contraction to precede ventricular contraction</p> Signup and view all the answers

    What does the term 'systole' refer to in cardiac physiology?

    <p>The phase of heart contraction</p> Signup and view all the answers

    What does the QRS complex in an ECG primarily represent?

    <p>Ventricular depolarization</p> Signup and view all the answers

    Which condition is indicated by a flatter T wave in an ECG?

    <p>Coronary artery disease</p> Signup and view all the answers

    What does an enlarged Q wave in an ECG typically indicate?

    <p>Myocardial infarction</p> Signup and view all the answers

    What does the P-Q interval represent?

    <p>Time from atrial excitation to ventricular excitation</p> Signup and view all the answers

    Which wave indicates ventricular repolarization in an ECG?

    <p>T wave</p> Signup and view all the answers

    How does ventricular depolarization contrast with repolarization in terms of ECG representation?

    <p>Depolarization is longer and broader than repolarization</p> Signup and view all the answers

    What does an enlarged R wave usually indicate in terms of cardiac physiology?

    <p>Enlarged ventricles</p> Signup and view all the answers

    What physiological change causes a lengthening of the P-Q interval?

    <p>Scar tissue from previous heart conditions</p> Signup and view all the answers

    What anatomical difference allows the left ventricle to generate higher pressures than the right ventricle?

    <p>Thicker myocardium in the left ventricle</p> Signup and view all the answers

    What is the primary reason for the parallel arrangement of blood vessels in the systemic circuit?

    <p>To ensure equal blood quality to all tissues</p> Signup and view all the answers

    Why is the hematocrit level in blood significant for physiological function?

    <p>It correlates with the oxygen-carrying capacity of hemoglobin</p> Signup and view all the answers

    What is a key advantage of the series arrangement of blood vessels in the pulmonary circuit?

    <p>It simplifies the exchange of gases at the alveoli</p> Signup and view all the answers

    What volume of blood does the average adult human contain?

    <p>5.5 liters</p> Signup and view all the answers

    What characterizes Heart Failure with Preserved Ejection Fraction (HFpEF)?

    <p>A stiff ventricle that struggles to relax</p> Signup and view all the answers

    Which of the following factors influences cardiac output?

    <p>Heart contractility and blood volume</p> Signup and view all the answers

    What is the typical ejection fraction (EF) range indicating a normal heart function?

    <p>55-70%</p> Signup and view all the answers

    During intense exercise, cardiac output can significantly increase to which range?

    <p>25-30 L/min</p> Signup and view all the answers

    Which neurotransmitter primarily supports the effects of norepinephrine on heart function?

    <p>Epinephrine</p> Signup and view all the answers

    What happens to parasympathetic input during increased physical activity?

    <p>It decreases, leading to higher heart rates</p> Signup and view all the answers

    What is a primary function of the β1 adrenergic receptors in the heart?

    <p>Significantly influence heart function</p> Signup and view all the answers

    What is the intrinsic firing rate of the SA nodal cells, and how does it compare to resting heart rate?

    <p>100 bpm; resting rate is slower</p> Signup and view all the answers

    What primarily facilitates the atrial kick during the cardiac cycle?

    <p>Atrial contractile cells</p> Signup and view all the answers

    Which phase of the cardiac action potential is characterized by calcium influx that maintains a plateau?

    <p>Phase 2</p> Signup and view all the answers

    Which statement accurately describes the function of the Bundle of His in the cardiac conduction system?

    <p>It conducts impulses to the ventricles.</p> Signup and view all the answers

    In what way do nodal cells differ from contractile cells in the heart?

    <p>They exhibit pacemaker potentials.</p> Signup and view all the answers

    What occurs during the relative refractory period in cardiac muscle?

    <p>Some Na+ channels recover, permitting potential action potentials.</p> Signup and view all the answers

    What role does excitation-contraction coupling play in cardiac muscle function?

    <p>It links electrical signals to muscle contraction.</p> Signup and view all the answers

    Which phase of the cardiac cycle occupies approximately 2/3 of the total cycle duration?

    <p>Diastole</p> Signup and view all the answers

    How does the vascular arrangement in series affect blood flow during gas exchange in circulation?

    <p>It enhances the efficiency of gas exchange.</p> Signup and view all the answers

    What is the mechanism of calcium-induced calcium release (CICR) in cardiac muscle contraction?

    <p>Calcium binds to troponin, initiating actin interaction.</p> Signup and view all the answers

    How is stroke volume calculated?

    <p>Stroke Volume = End-Diastolic Volume - End-Systolic Volume</p> Signup and view all the answers

    Which ion channels play a critical role in the rapid repolarization phase of the cardiac action potential?

    <p>K+ channels</p> Signup and view all the answers

    What is mainly prevented by the absolute refractory period in cardiac muscle tissue?

    <p>Tetanic contractions</p> Signup and view all the answers

    During which phase of the cardiac cycle do the ventricles eject blood into the major arteries?

    <p>Ejection</p> Signup and view all the answers

    What defines cardiac output?

    <p>The volume of blood ejected per minute from each ventricle.</p> Signup and view all the answers

    Which of the following describes the main function of refractory periods in the heart?

    <p>Prevent arrhythmias and allow the heart to refill with blood.</p> Signup and view all the answers

    What is the average stroke volume at rest in mL?

    <p>70 mL</p> Signup and view all the answers

    How does increased end-diastolic volume (EDV) primarily influence stroke volume?

    <p>It leads to enhanced filament overlap and stronger contractions.</p> Signup and view all the answers

    What is the effect of sympathetic stimulation on stroke volume independent of EDV?

    <p>It increases stroke volume by enhancing calcium availability.</p> Signup and view all the answers

    What impact does increased afterload have on stroke volume?

    <p>It decreases stroke volume and makes ventricular contraction harder.</p> Signup and view all the answers

    What relationship exists between heart rate and stroke volume during strenuous exercise?

    <p>Heart rate rises while stroke volume plateaus after a certain point.</p> Signup and view all the answers

    What is the primary purpose of an electrocardiogram (ECG)?

    <p>To diagnose heart conditions by recording electrical activity.</p> Signup and view all the answers

    Which statement about the Frank-Starling mechanism is correct?

    <p>It ensures equal output from both right and left ventricles.</p> Signup and view all the answers

    What aspect of cardiac output distribution changes during exercise compared to rest?

    <p>It increases to support skeletal muscle activity during exercise.</p> Signup and view all the answers

    Which factor primarily limits stroke volume in a failing heart?

    <p>Increased wall stress.</p> Signup and view all the answers

    What is the primary reason for the left ventricle's thicker myocardium compared to the right ventricle?

    <p>It generates higher pressure for systemic circulation.</p> Signup and view all the answers

    How does the arrangement of blood vessels in the systemic circuit primarily affect blood flow regulation?

    <p>It allows for better regulation of blood flow.</p> Signup and view all the answers

    What is the average hematocrit percentage in blood volume?

    <p>40-45%</p> Signup and view all the answers

    Which of the following best describes the components of blood?

    <p>Plasma and its cellular components</p> Signup and view all the answers

    What primarily distinguishes the pulmonary circulation from systemic circulation in the cardiovascular system?

    <p>The pressure required for blood flow.</p> Signup and view all the answers

    What effect does increased end-diastolic volume (EDV) have on stroke volume?

    <p>It enhances filament overlap, leading to stronger contractions.</p> Signup and view all the answers

    How does sympathetic stimulation influence stroke volume?

    <p>It increases stroke volume without changing end-diastolic volume.</p> Signup and view all the answers

    What is the impact of increased afterload on stroke volume?

    <p>It decreases stroke volume, making ventricles contract harder.</p> Signup and view all the answers

    What occurs to cardiac output during strenuous exercise?

    <p>Heart rate rises linearly while stroke volume plateaus after a certain point.</p> Signup and view all the answers

    What is the primary purpose of an electrocardiogram (ECG)?

    <p>To assess the electrical activity and identify heart conditions.</p> Signup and view all the answers

    What does the net sum of electrical potentials from cardiac muscle cells represent in an ECG?

    <p>The heart's electrical activity.</p> Signup and view all the answers

    What indicates the potential for blood to back up into veins and capillaries?

    <p>Increased end-diastolic volume.</p> Signup and view all the answers

    Why is understanding cardiovascular dynamics crucial for health assessment?

    <p>It assists in evaluating heart performance and health during activities.</p> Signup and view all the answers

    What is the average stroke volume at rest?

    <p>70 mL</p> Signup and view all the answers

    What phase of the cardiac cycle involves blood flowing passively from atria to ventricles?

    <p>Ventricular Filling</p> Signup and view all the answers

    What is the normal range of ejection fraction values that may indicate healthy cardiac function?

    <p>55-70%</p> Signup and view all the answers

    Which factor primarily contributes to the increase in cardiac output during intense exercise?

    <p>Increased sympathetic activity</p> Signup and view all the answers

    How is cardiac output (CO) defined?

    <p>The volume of blood ejected per minute</p> Signup and view all the answers

    What characterizes Heart Failure with Reduced Ejection Fraction (HFrEF)?

    <p>Systolic dysfunction</p> Signup and view all the answers

    What does the relative refractory period allow in cardiac muscle cells?

    <p>The potential for initiating new action potentials</p> Signup and view all the answers

    What primarily controls blood flow in a parallel arrangement of blood vessels?

    <p>Lower total resistance</p> Signup and view all the answers

    Which statement correctly describes the effects of the parasympathetic nervous system on heart function?

    <p>Keeps heart rate around 70 bpm during rest</p> Signup and view all the answers

    During which phase of the cardiac cycle does the pressure build-up occur?

    <p>Isovolumetric Contraction</p> Signup and view all the answers

    What happens to the intrinsic firing rate of SA nodal cells when physical activity increases?

    <p>It remains unchanged at 100 bpm</p> Signup and view all the answers

    Which of the following best describes the relationship between stroke volume and cardiac output?

    <p>Cardiac output equals stroke volume multiplied by heart rate</p> Signup and view all the answers

    What is the role of refractory periods in maintaining heart function?

    <p>They prevent rapid and inefficient heart contractions</p> Signup and view all the answers

    How are stroke volume (SV) and end-diastolic volume (EDV) related mathematically?

    <p>SV = EDV - ESV</p> Signup and view all the answers

    When is the parasympathetic input to the heart reduced significantly?

    <p>During vigorous exercise</p> Signup and view all the answers

    What is the significance of beta-adrenergic receptors in cardiac function?

    <p>They regulate heart function through calcium influx</p> Signup and view all the answers

    Which factor has the greatest impact on resistance within blood vessels?

    <p>Vessel radius</p> Signup and view all the answers

    What is the primary function of the cardiac myocytes' gap junctions?

    <p>To allow rapid electrical communication between cells</p> Signup and view all the answers

    Which of the following heart valves prevents backflow from arteries to ventricles?

    <p>Pulmonary valve</p> Signup and view all the answers

    In terms of blood circulation, how does the cardiovascular system primarily maintain body temperature?

    <p>By facilitating heat exchange via blood flow</p> Signup and view all the answers

    Which layer of the heart serves as the innermost layer separating heart chambers from the myocardium?

    <p>Endocardium</p> Signup and view all the answers

    Which method of communication is pivotal in the modulation of heart rate and contractility by the autonomic nervous system?

    <p>Neurotransmitter action on receptors</p> Signup and view all the answers

    Which physiological feature characterizes the myocardium of the heart?

    <p>Cardiac muscle fibers with a striated appearance</p> Signup and view all the answers

    What primarily drives blood flow in the cardiovascular system according to Ohm's Law?

    <p>Pressure gradient between two points</p> Signup and view all the answers

    Which type of receptor is crucial for the sympathetic regulation of cardiovascular function?

    <p>Adrenergic receptors</p> Signup and view all the answers

    Which process is central to ensuring one-way blood flow in the heart?

    <p>Presence of valves</p> Signup and view all the answers

    What is the primary reason for the left ventricle having a thicker myocardium compared to the right ventricle?

    <p>The left ventricle must generate higher pressure for systemic circulation.</p> Signup and view all the answers

    Which statement accurately describes the significance of the blood vessel arrangement in the systemic circuit?

    <p>Parallel arrangement allows for selective distribution of blood to various tissues.</p> Signup and view all the answers

    What component of blood constitutes the largest volume percentage?

    <p>Plasma</p> Signup and view all the answers

    Which function reflects a primary role of the cardiovascular system in maintaining homeostasis?

    <p>Delivering nutrients and removing waste from cells.</p> Signup and view all the answers

    In terms of blood volume, what is the average total volume of blood in an adult human body?

    <p>Approximately 5.5 liters</p> Signup and view all the answers

    Which phase of the cardiac action potential corresponds to the rapid repolarization due to the closure of Ca2+ channels and the opening of K+ channels?

    <p>Phase 3</p> Signup and view all the answers

    What is the primary role of the Purkinje fibers in the cardiac conduction system?

    <p>Ensuring rapid ventricular contraction</p> Signup and view all the answers

    What distinguishes the excitation-contraction coupling mechanism in cardiac muscle compared to skeletal muscle?

    <p>Calcium-induced calcium release (CICR) is key</p> Signup and view all the answers

    In terms of ion channels, what role do L-type calcium channels play in the action potential of cardiac muscle cells?

    <p>They help maintain the plateau phase during repolarization</p> Signup and view all the answers

    Which of the following correctly describes a key functional characteristic of cardiac muscle cells?

    <p>They are dependent solely on aerobic metabolism</p> Signup and view all the answers

    Which of the following best describes the significance of functional syncytium in cardiac muscle tissue?

    <p>It enables rapid communication and synchronized contractions</p> Signup and view all the answers

    How does the AV node contribute to the timing of cardiac contractions?

    <p>By introducing a delay to ensure proper timing between atrial and ventricular contraction</p> Signup and view all the answers

    What role do gap junctions play in maintaining cardiac function?

    <p>They allow for rapid communication and synchronization among cardiac muscle cells</p> Signup and view all the answers

    What factor has the most significant influence on blood flow resistance in the cardiovascular system?

    <p>Vessel radius</p> Signup and view all the answers

    Which structures in the heart ensure one-way blood flow?

    <p>Heart valves</p> Signup and view all the answers

    Which receptor types are primarily involved in enhancing heart rate and contractility?

    <p>Beta adrenergic receptors</p> Signup and view all the answers

    Which cardiac tissue layer serves as a protective covering of the heart?

    <p>Epicardium</p> Signup and view all the answers

    What initiates the sequence of electrical events in the conduction pathway of the heart?

    <p>SA node</p> Signup and view all the answers

    In which cardiovascular regulation does the autonomic nervous system exert its influence?

    <p>Heart rate and contractility</p> Signup and view all the answers

    Which characteristic differentiates cardiac muscle cells from both skeletal and smooth muscle cells?

    <p>Branched ends for interconnection</p> Signup and view all the answers

    What is a crucial outcome of the pressure gradient in blood circulation?

    <p>Drives blood flow</p> Signup and view all the answers

    What does Ohm's Law primarily describe in the context of the cardiovascular system?

    <p>Relationship between blood pressure and flow rate</p> Signup and view all the answers

    What is the primary role of gap junctions in cardiac muscle cells?

    <p>Allow rapid communication between cells</p> Signup and view all the answers

    What effect does increased end-diastolic volume (EDV) have on stroke volume?

    <p>Increases stroke volume by enhancing filament overlap</p> Signup and view all the answers

    How does sympathetic stimulation primarily increase stroke volume?

    <p>By increasing calcium availability for stronger contractions</p> Signup and view all the answers

    What does the Frank-Starling Law ensure regarding the right and left ventricles?

    <p>That the output of both ventricles is balanced</p> Signup and view all the answers

    What happens to stroke volume during strenuous exercise?

    <p>It plateaus after a certain point despite increased heart rate</p> Signup and view all the answers

    What is the primary function of an electrocardiogram (ECG)?

    <p>To assess the electrical activity of the heart</p> Signup and view all the answers

    What could potentially decrease stroke volume in a healthy heart?

    <p>Low preload levels</p> Signup and view all the answers

    How does increased afterload affect stroke volume?

    <p>It decreases stroke volume, making contraction more difficult</p> Signup and view all the answers

    What characterizes the cardiovascular response during physical activity?

    <p>Increased heart rate and plateauing stroke volume work together</p> Signup and view all the answers

    Which statement regarding the phases of the cardiac cycle is accurate?

    <p>Diastole predominantly allows the heart to refill with blood.</p> Signup and view all the answers

    What physiological significance do refractory periods have in maintaining heart function?

    <p>They ensure time for the heart to refill with blood.</p> Signup and view all the answers

    Which factor primarily influences stroke volume as per its definition?

    <p>End-systolic volume reduction.</p> Signup and view all the answers

    During which phase of the cardiac cycle does isovolumetric relaxation occur?

    <p>After ventricular ejection.</p> Signup and view all the answers

    How is cardiac output calculated?

    <p>CO = Heart Rate (HR) x Stroke Volume (SV).</p> Signup and view all the answers

    What happens to sodium channels during the absolute refractory period?

    <p>They are inactive, preventing new action potentials.</p> Signup and view all the answers

    Which phase of the cardiac cycle is characterized by atrial contraction?

    <p>Atrial kick.</p> Signup and view all the answers

    What is the primary role of the relative refractory period (RRP) in cardiac muscle?

    <p>Allowing the initiation of new contractions.</p> Signup and view all the answers

    Why does the left ventricle have a thicker myocardium compared to the right ventricle?

    <p>To generate higher pressure for systemic circulation</p> Signup and view all the answers

    What is the primary component of blood making up the majority of its volume?

    <p>Plasma</p> Signup and view all the answers

    How does the arrangement of blood vessels in the systemic circuit differ from that in the pulmonary circuit?

    <p>Systemic arrangement is in parallel while pulmonary is in series</p> Signup and view all the answers

    What role does blood play in the cardiovascular system?

    <p>It acts as a transport medium for nutrients and waste</p> Signup and view all the answers

    What is the significance of the parallel arrangement of blood vessels in the systemic circuit?

    <p>It provides better regulation of blood flow to various tissues</p> Signup and view all the answers

    What is the role of the AV node in cardiac conduction?

    <p>To delay the impulse for proper timing</p> Signup and view all the answers

    During which phase of the cardiac action potential does initial repolarization occur?

    <p>Phase 1</p> Signup and view all the answers

    What mechanism is essential for excitation-contraction coupling in cardiac muscle?

    <p>Calcium-induced calcium release</p> Signup and view all the answers

    Which structures in the conduction system distribute signals to the ventricles?

    <p>Bundle branches</p> Signup and view all the answers

    How does calcium intake influence cardiac muscle contraction?

    <p>It controls contraction strength and duration</p> Signup and view all the answers

    What term describes the coordinated contraction of cardiac muscle cells due to electrical connections?

    <p>Functional syncytium</p> Signup and view all the answers

    Which ion channels play a key role in maintaining the plateau phase of the cardiac action potential?

    <p>L-type calcium channels</p> Signup and view all the answers

    What does the term parallel arrangement in vascular circulation refer to?

    <p>Each tissue receives blood of equal quality</p> Signup and view all the answers

    What occurs during the isovolumetric contraction phase of the cardiac cycle?

    <p>Ventricles contract with all valves closed, increasing pressure.</p> Signup and view all the answers

    What does stroke volume represent in cardiac function?

    <p>The volume of blood ejected from each ventricle per beat.</p> Signup and view all the answers

    Why are refractory periods critical in cardiac function?

    <p>They prevent arrhythmias by allowing time for the heart to refill.</p> Signup and view all the answers

    How is cardiac output defined?

    <p>The volume of blood ejected from each ventricle per minute.</p> Signup and view all the answers

    What is the primary function of the cardiac cycle's diastole phase?

    <p>To facilitate ventricular filling and heart refilling with blood.</p> Signup and view all the answers

    Which of the following describes the role of venules in the circulatory system?

    <p>To collect blood from capillaries before returning it through veins.</p> Signup and view all the answers

    What is the average stroke volume at rest?

    <p>70 mL</p> Signup and view all the answers

    Which equation correctly expresses the relationship between cardiac output, heart rate, and stroke volume?

    <p>CO = HR x SV</p> Signup and view all the answers

    What is the typical resting cardiac output?

    <p>5 L/min</p> Signup and view all the answers

    Which type of heart failure is characterized by a stiff ventricle that struggles to relax?

    <p>Heart Failure with Preserved Ejection Fraction (HFpEF)</p> Signup and view all the answers

    What is the typical range of ejection fraction values indicating normal heart function?

    <p>55-70%</p> Signup and view all the answers

    Which system primarily dominates heart rate control at rest?

    <p>Parasympathetic nervous system</p> Signup and view all the answers

    What happens to parasympathetic input as physical activity increases?

    <p>It decreases</p> Signup and view all the answers

    Which receptor type is most significant in regulating heart function?

    <p>β1 receptors</p> Signup and view all the answers

    What is the intrinsic firing rate of SA nodal cells?

    <p>100 bpm</p> Signup and view all the answers

    During which type of heart failure is systolic dysfunction typically seen?

    <p>Heart Failure with Reduced Ejection Fraction (HFrEF)</p> Signup and view all the answers

    What effect does increased preload have on stroke volume?

    <p>Increases stroke volume due to enhanced filament overlap</p> Signup and view all the answers

    How does sympathetic stimulation affect stroke volume?

    <p>It increases stroke volume without changing end-diastolic volume</p> Signup and view all the answers

    What is the impact of increased afterload on stroke volume?

    <p>It decreases stroke volume by making contraction more difficult</p> Signup and view all the answers

    During strenuous exercise, which statement about cardiac output is true?

    <p>Cardiac output rises due to an increase in heart rate and stable stroke volume</p> Signup and view all the answers

    What does an electrocardiogram (ECG) measure?

    <p>The electrical activity of the heart</p> Signup and view all the answers

    Why is the Frank-Starling mechanism important in cardiac physiology?

    <p>It ensures the output of both ventricles remains balanced</p> Signup and view all the answers

    What is the purpose of maintaining adequate cardiac output at rest?

    <p>To sustain vital organ function effectively</p> Signup and view all the answers

    How does increased heart rate affect cardiac output during physical activity?

    <p>Both heart rate and stroke volume work together to elevate cardiac output</p> Signup and view all the answers

    Study Notes

    Cardiac Muscle and Electrical Activity

    • Atrial contractile cells facilitate the atrial kick, contributing to ventricular filling.
    • The AV node introduces a delay in conduction to allow for proper ventricular filling.
    • The conduction system ensures the coordinated and efficient spread of electrical impulses throughout the heart.
    • Components of the Conduction System:
      • The Bundle of His conducts the impulse to the ventricles.
      • Bundle branches distribute signals to the right and left ventricles.
      • Purkinje fibers facilitate rapid contraction of the ventricular muscle.
    • Cardiac muscle cells are connected via gap junctions.
    • Gap junctions allow for rapid communication and synchronization of electrical impulses between cells.
    • This creates a functional syncytium, enabling coordinated heartbeats.

    Cardiac Action Potentials

    • Cardiac muscle cells exhibit action potentials with distinct phases.
    • Phase 0: Rapid depolarization driven by sodium ion (Na+) influx through fast sodium channels.
    • Phase 1: Initial repolarization caused by closure of fast sodium channels.
    • Phase 2: Plateau phase maintained by calcium ion (Ca2+) influx through L-type calcium channels.
    • Phase 3: Rapid repolarization due to closure of L-type calcium channels and opening of potassium ion (K+) channels.
    • Phase 4: Establishment of the resting membrane potential.

    Differences Among Cell Types:

    • Nodal cells exhibit spontaneous pacemaker potentials, initiating heartbeats.
    • Conducting cells possess unique ion channel profiles for efficient conduction of impulses
    • Contractile cells lack spontaneous action potential generation but contract in response to electrical stimulation.

    Ion Channels Involved:

    • Fast sodium channels are crucial for rapid depolarization in cardiac action potentials.
    • L-type calcium channels contribute to the plateau phase.
    • Potassium channels are essential for repolarization.

    Excitation-Contraction Coupling:

    • Calcium-induced calcium release (CICR) plays a central role.
    • Trigger Ca2+ enters through L-type channels, triggering the release of more Ca2+ from the sarcoplasmic reticulum (SR) via ryanodine receptors.
    • Steps in Contraction:
      • Ca2+ binds to troponin, exposing actin binding sites.
      • Cross-bridge cycling occurs, generating force.
      • Ca2+ is pumped back into the SR and extracellular fluid for relaxation.

    Role of Calcium:

    • Essential for initiating contraction in cardiac muscle.
    • Regulates the strength and duration of muscle contraction.
    • Involves both extracellular and intracellular calcium sources.

    Vascular Arrangement:

    • Parallel arrangement of vessels allows for equal blood quality to all tissues.
    • Series arrangement in the pulmonary circuit ensures proper gas exchange.
    • Total resistance is lower in parallel systems, enhancing blood flow.

    Sequence of Blood Vessels:

    • Blood flows from arteries to arterioles, then to capillaries.
    • Venules collect blood before it returns through veins.

    Refractory Periods in Cardiac Muscle:

    • Absolute refractory period (ARP):
      • No new action potential can be initiated.
      • Fast sodium channels are inactive during this phase.
      • Prevents tetanic contractions in cardiac muscle.
    • Relative refractory period (RRP):
      • Some sodium channels recover, allowing potential for new action potential generation.
      • Occurs as the cell membrane approaches full repolarization.
      • Important for maintaining rhythmic heart contractions.

    Physiological Significance of Refractory Periods:

    • They ensure proper heart function.
    • Allow time for the heart to refill with blood.
    • Critical for preventing arrhythmias and maintaining cardiac output.

    The Cardiac Cycle:

    • The cardiac cycle consists of two main phases: diastole (relaxation) and systole (contraction).
    • Diastole occupies about 2/3 of the cycle, while systole takes up 1/3.

    Four Phases of the Cardiac Cycle:

    • Ventricular filling (Diastole): Blood flows passively from atria to ventricles, followed by the atrial kick.
    • Isovolumetric contraction (Systole): Ventricles contract with all valves closed, leading to pressure buildup.
    • Ejection (Systole): Ventricles eject blood into the aorta and pulmonary artery as valves open.
    • Isovolumetric relaxation (Diastole): Ventricles relax with all valves closed, preparing for the next cycle.

    Stroke Volume (SV):

    • Defined as the volume of blood ejected from each ventricle per beat.
    • Calculated as: SV = EDV - ESV.
    • Average stroke volume is approximately 70 mL at rest.

    Cardiac Output and Its Regulation:

    • Cardiac output (CO) is the volume of blood ejected from each ventricle per minute.
    • Calculated as: CO = HR x SV.
    • Most cells within 10 µm of a capillary for efficient exchange.

    Hormone and Signaling Molecule Distribution:

    • Facilitates communication between different parts of the body.
    • Enables rapid response to physiological changes.

    Temperature Regulation:

    • Helps maintain body temperature through blood circulation.
    • Allows for heat distribution and dissipation.

    Pressure, Flow, and Resistance in the Cardiovascular System:

    • Ohm's Law: Flow (F or Q) = Pressure difference (ΔP) / Resistance (R).
    • Pressure gradient, not absolute pressure, drives blood flow.

    Factors Affecting Resistance:

    • Vessel length (L): Longer vessels have higher resistance.
    • Blood viscosity (η): Increased viscosity leads to higher resistance.
    • Vessel radius (r): Most significant factor (raised to the 4th power) - smaller radius means higher resistance.

    Impact of Vessel Radius:

    • Small changes in radius can dramatically affect resistance and flow.
    • Key mechanism for regulating blood flow to different organs.

    Heart Structure and Function:

    • Heart valves ensure one-way blood flow through the heart.
    • Two types: Atrioventricular (AV) and Semilunar (SL) valves.

    Atrioventricular Valves:

    • Right AV (tricuspid) and Left AV (bicuspid/mitral).
    • Prevent backflow from ventricles to atria.

    Semilunar Valves:

    • Pulmonary and Aortic semilunar valves.
    • Prevent backflow from arteries to ventricles.

    Heart Tissue Layers:

    • Endocardium: Innermost layer, separates chambers from myocardium.
    • Myocardium: Thick layer of cardiac muscle.
    • Epicardium: Outer protective layer.
    • Pericardium: Fluid-filled sac surrounding the heart.

    Cardiac Muscle Cells and Electrical Activity:

    • Cardiac myocyte characteristics:
      • Striated appearance.
      • Mostly mononucleated.
      • Branched ends for interconnection.

    Electrical Connections:

    • Gap junctions allow rapid communication between cells.
    • Forms a functional syncytium for coordinated contraction.

    Comparison with Skeletal and Smooth Muscle:

    • Similarities to skeletal muscle:
      • Presence of sarcomeres and striations.
      • Contains troponin for calcium-mediated contraction.
      • Presence of T-tubules.
    • Similarities to smooth muscle:
      • Presence of pacemaker cells.
      • Gap junctions forming a syncytium.
      • Calcium entry from extracellular fluid.
      • Modulation by autonomic nervous system and hormones.

    Cardiovascular System Regulation:

    • Autonomic nervous system control: Sympathetic and parasympathetic influences on heart rate and contractility.

    Receptor Types in Cardiovascular Regulation:

    • Cholinergic Receptors:
      • Nicotinic acetylcholine receptors (nAChR) at autonomic ganglia.
      • Muscarinic acetylcholine receptors (mAChR) on target tissues.
    • Adrenergic Receptors:
      • Beta (β) receptors, particularly β1 and β2.
      • Alpha (α) receptors, focusing on α1.
      • Important targets for therapeutic interventions in cardiovascular diseases.

    Conduction Pathway of the Heart:

    • Sequence of electrical events:
      • Begins with the SA node, the primary pacemaker.
      • The impulse travels to the AV node, causing a delay.
      • The impulse then proceeds through the Bundle of His, bundle branches, and Purkinje fibers.
      • This coordinated conduction ensures efficient ventricular contraction.

    Cardiovascular System Components

    • The cardiovascular system consists of three main components: the heart, blood, and vasculature.
    • The heart is a biological pump that generates forceful contractions to move blood throughout the body.
    • Blood is a transport medium composed of plasma, red blood cells, white blood cells, and platelets.
    • Vasculature includes blood vessels that carry blood throughout the body.
    • Vasculature is divided into pulmonary and systemic circuits.
    • Pulmonary circulation: transports blood to and from the lungs to become oxygenated.
    • Systemic circulation: carries oxygenated blood to the rest of the body.

    Cardiovascular System Roles in Homeostasis

    • The cardiovascular system plays crucial roles in maintaining homeostasis, including nutrient and waste transport, hormone and signaling molecule distribution, and temperature regulation.
    • The cardiovascular system delivers nutrients and removes waste products from cells via capillaries.
    • Most cells in the body are located within 10µm of a capillary to ensure efficient exchange.
    • The cardiovascular system facilitates communication between different parts of the body by transporting hormones and other signaling molecules.
    • The cardiovascular system helps maintain core body temperature through blood circulation, allowing for heat distribution and dissipation.

    Pressure, Flow, and Resistance in the Cardiovascular System

    • Ohm's Law applies to cardiovascular flow: Flow (F or Q) = Pressure difference (ΔP)/ Resistance (R).
    • Pressure gradient, NOT absolute pressure, drives blood flow within the cardiovascular system.
    • Factors that affect resistance within blood vessels include vessel length, blood viscosity, and most importantly - vessel radius.
    • Small changes in vessel radius have a significant impact on resistance and blood flow.
    • This makes it a key mechanism in regulating blood flow to different organs.

    Heart Structure and Function

    • Heart Valves:
      • Atrioventricular (AV) Valves: prevent backflow from ventricles to atria:
        • Tricuspid Valve: Right AV valve.
        • Bicuspid (Mitral) Valve: Left AV valve.
      • Semilunar (SL) Valves: prevent backflow from arteries to ventricles:
        • Pulmonary Valve
        • Aortic Valve
    • Heart Tissue Layers:
      • Endocardium: Innermost layer that separates chambers from myocardium.
      • Myocardium: Thick layer of cardiac muscle.
      • Epicardium: Protective outer layer.
      • Pericardium: Fluid-filled sac that surrounds the heart.

    Cardiac Muscle Cells and Electrical Activity

    • Cardiac Myocyte Characteristics:
      • Striated appearance.
      • Mostly mononucleated.
      • Branched ends allowing for interconnection between cells.
    • Electrical Connections:
      • Gap junctions allow for rapid communication between cells for synchronized and coordinated contraction.
      • The heart is a functional syncytium due to electrical connections between cells.
    • Comparison to Other Muscle Types:
      • Skeletal muscle similarities: striations, sarcomeres, troponin for calcium-mediated contraction, and T-tubules.
      • Smooth muscle similarities: pacemaker cells, gap junctions, calcium entry from extracellular fluid, modulation by autonomic nervous system and hormones.

    Cardiovascular System Regulation

    • Autonomic Nervous System Control:
      • Sympathetic nervous system: increases heart rate and contractility.
      • Parasympathetic nervous system: slows heart rate and weakens atrial contraction.
    • Receptor Types in Cardiovascular Regulation:
      • Cholinergic receptors:
        • Nicotinic acetylcholine receptors (nAChR) at autonomic ganglia.
        • Muscarinic acetylcholine receptors (mAChR) on target tissues.
      • Adrenergic receptors:
        • Beta (β) receptors, particularly β1 and β2.
        • Alpha (α) receptors, focusing on α1.
        • These receptor types offer targets for therapeutic interventions in cardiovascular diseases.

    Conduction Pathway of the Heart

    • Sequence of Electrical Events:
      • Sinoatrial (SA) node: primary pacemaker, initiating the electrical impulse for heartbeat.
      • Atrial contractile cells: facilitate the atrial kick to push blood into ventricles.
      • Atrioventricular (AV) node: introduces a delay for proper timing to allow for ventricular filling.
    • Components of the Conduction System:
      • Bundle of His: conducts the impulse to the ventricles.
      • Bundle branches: distribute the signals to the ventricles.
      • Purkinje fibers: ensure rapid contraction of the ventricular muscle.
    • Importance of Electrical Connections:
      • Gap junctions connect cardiac muscle cells for rapid communication and synchronization.
      • The functional syncytium ensures coordinated heartbeats.

    Cardiac Action Potentials

    • Phases of Action Potentials:
      • Phase 0: Rapid depolarization due to sodium influx.
      • Phase 1: Initial repolarization as sodium channels close.
      • Phase 2: Plateau phase maintained by calcium influx.
      • Phase 3: Rapid repolarization as calcium channels close and potassium channels open.
      • Phase 4: Resting membrane potential re-established.
    • Differences Among Cell Types:
      • Nodal cells: exhibit pacemaker potentials.
      • Conducting cells: have unique ion channel profiles.
      • Contractile cells: lack spontaneous action potential generation.
    • Ion Channels Involved:
      • Fast sodium channels: rapid depolarization.
      • L-type calcium channels: plateau phase.
      • Potassium channels: repolarization.

    Excitation-Contraction Coupling

    • Mechanism Overview: Calcium-induced calcium release (CICR) is key.
      • Trigger calcium: enters through L-type calcium channels.
      • Ryanodine receptors: release more calcium from the sarcoplasmic reticulum (SR).
    • **Steps in Contraction
      • Calcium binds to troponin, exposing actin's binding sites.
      • Cross-bridge cycling occurs, generating force.
      • Calcium pumped back into the SR and ECF for relaxation.
    • The Role of Calcium:
      • Essential for initiating contraction.
      • Regulates strength and duration of muscle contraction.
      • Involves both extracellular and intracellular calcium sources.

    Vascular Arrangement

    • Parallel vs. Series Circulation:
      • Parallel arrangement: allows for equal blood quality to all tissues.
      • Series arrangement in the pulmonary circuit: ensures proper gas exchange.
      • Total resistance is lower in parallel systems: enhancing blood flow.
    • Sequence of Blood Vessels:
      • Blood flow from arteries to arterioles, then capillaries.
      • Venules collect blood before it returns through veins.

    Refractory Periods in Cardiac Muscle

    • Absolute Refractory Period (ARP):
      • No new action potential can be initiated.
      • Fast sodium channels are inactive during this phase.
      • Prevents tetanic contractions in cardiac muscle.
    • Relative Refractory Period (RRP):
      • Some sodium channels recover, allowing the potential for new action potentials.
      • Occurs as the cell membrane approaches full repolarization.
      • Essential for maintaining rhythmic heart contractions.
    • Physiological Significance:
      • Refractory periods ensure proper heart function.
      • Allow time for the heart to refill with blood.
      • Critical for preventing arrhythmias and maintaining cardiac output.

    The Cardiac Cycle

    • Overview: Consists of two main phases: diastole (relaxation) and systole (contraction).
      • Diastole takes up 2/3 of the cycle.
      • Systole takes up 1/3 of the cycle.
    • Four Phases of the Cardiac Cycle:
      • Ventricular Filling (Diastole): Blood flows passively from atria to ventricles, followed by the atrial kick.
      • Isovolumetric Contraction (Systole): Ventricles contract with all valves closed, leading to pressure build-up.
      • Ejection (Systole): Ventricles eject blood into the aorta and pulmonary artery as valves open.
      • Isovolumetric Relaxation (Diastole): Ventricles relax with all valves closed, preparing for the next cycle.

    Stroke Volume (SV)

    • Defined as the volume of blood ejected from each ventricle per beat.
    • Calculated as SV = End-Diastolic Volume (EDV) - End-Systolic Volume (ESV).
    • Average stroke volume is approximately 70 mL at rest.

    Cardiac Output and Its Regulation

    • Definition of Cardiac Output (CO): The volume of blood ejected from each ventricle per minute.
    • Calculation: CO = Heart Rate (HR) x Stroke Volume (SV).
    • Average Values: Typical resting values: 70 beats/min and 70 mL/beat, resulting in approximately 5 L/min of cardiac output.
    • Regulation: Influences include autonomic nervous system activity, blood volume, and heart contractility.
    • β1 receptors: found in the heart play a significant role in regulating cardiac function.

    Ejection Fractions and Heart Failure

    • Heart Failure with Preserved Ejection Fraction (HFpEF): Characterized by a stiff ventricle that struggles to relax, indicating diastolic dysfunction.
    • Heart Failure with Reduced Ejection Fraction (HFrEF): Traditionally recognized as heart failure, indicating systolic dysfunction.
    • Ejection Fraction (EF): Measures the heart's efficiency, usually calculated from the left ventricle.
      • Typical EF values: 55-70%, lower values indicate potential heart failure.

    Clinical Relevance

    • Understanding cardiac function is essential for diagnosing and managing heart conditions.

    Autonomic Innervation of the Heart

    • Parasympathetic Effects:
      • Slow heart rate and weakens atrial contraction.
      • Reduces conduction speed through the AV node.
    • Sympathetic Effects:
      • Increases heart rate and enhances ventricular contraction strength.
      • Norepinephrine (NE) acts immediately, while epinephrine (Epi) supports NE effects.

    Control of Heart Rate

    • Resting State:
      • Parasympathetic input dominates, keeping heart rate around 70 bpm.
      • Sympathetic input is minimal, allowing for lower heart rate.
    • Increased Physical Activity:
      • Physical activity decreases parasympathetic input and increases sympathetic input.
      • The intrinsic firing rate of SA nodal cells is 100 bpm, but resting heart rate is slower due to parasympathetic tone.

    ECG Wave Representations

    • S-T segment: Represents ventricular muscle fiber depolarization during the plateau phase of the action potential.
      • Elevated: Suggests acute myocardial infarction.
      • Depressed: Suggests insufficient oxygen supply to the heart muscle.
    • Q-T interval: Represents the time from the beginning of ventricular depolarization to the end of ventricular repolarization.
      • Lengthened: May indicate myocardial damage, ischemia, or conduction abnormalities.

    ECG Wave Timing in Relation to Cardiac Cycles

    • P wave: Represents atrial depolarization, which precedes atrial contraction (atrial systole).
    • QRS complex: Represents ventricular depolarization, which precedes ventricular contraction (ventricular systole).
    • T wave: Represents ventricular repolarization, which occurs as the ventricles begin relaxation (ventricular diastole).

    ECG Wave Analysis

    • P wave:
      • Larger than normal: May indicate atrial enlargement.
    • Q wave:
      • Enlarged: May indicate a myocardial infarction.
    • R wave:
      • Enlarged: Generally indicates enlarged ventricles.
    • T wave:
      • Flatter than normal: May suggest insufficient oxygen supply to the heart muscle, for example in coronary artery disease.
      • Elevated: May suggest hyperkalemia (high blood potassium level).

    Intervals and Segments

    • P-Q interval (also known as P-R interval): Represents the time from the beginning of atrial excitation to the beginning of ventricular excitation.
      • Lengthened: May indicate a detour of the action potential around scar tissue, possibly caused by coronary artery disease or rheumatic fever.

    Components of the Cardiovascular System

    • The heart is a biological pump generating force to move blood throughout the body.
    • Each heartbeat involves two main events: an electrical action potential and a mechanical contraction.
    • The left and right sides of the heart differ in structure and function.
    • The left ventricle has a thicker myocardium to generate higher pressure needed for systemic circulation.
    • Blood is a transport medium composed of plasma and cellular components.
    • Total blood volume averages 5.5 liters.
    • Hematocrit, the red blood cell volume, averages 42-45%.
    • The buffy coat contains leukocytes and platelets.
    • The vasculature (blood vessels) are not passive in blood movement.
    • Blood vessels are divided into pulmonary and systemic circuits.
    • The arrangement of blood vessels is crucial for efficient blood flow:
      • Parallel arrangement (systemic) allows for better regulation of blood flow.
      • Series arrangement (pulmonary) ensures proper gas exchange.

    Cardiovascular System Roles in Homeostasis

    • Nutrient and waste transport: delivers nutrients and removes waste products from cells.
    • Oxygen and carbon dioxide transport: facilitates gas exchange between lungs and tissues.
    • Hormone transport: distributes hormones throughout the body.
    • Temperature regulation: helps maintain body temperature.
    • Immune function: transports immune cells to fight infections.

    The Electrical Conduction System of the Heart

    • The sinoatrial (SA) node is the primary pacemaker, generating action potentials.
    • The atrioventricular (AV) node delays the impulse for proper timing.
    • The Bundle of His conducts the impulse from the AV node to the ventricles.
    • Bundle branches distribute the signal to the ventricles.
    • Purkinje fibers ensure rapid contraction of ventricular muscle.
    • Cardiac muscle cells connect via gap junctions, enabling rapid communication and synchronization.
    • This allows for a functional syncytium, ensuring coordinated heartbeats.

    Cardiac Action Potentials

    • Phase 0: Rapid depolarization due to sodium influx.
    • Phase 1: Initial repolarization as sodium channels close.
    • Phase 2: Plateau phase maintained by calcium influx.
    • Phase 3: Rapid repolarization as calcium channels close and potassium channels open.
    • Phase 4: Resting membrane potential is established.

    Differences Among Cell Types

    • Nodal cells exhibit pacemaker potentials.
    • Conducting cells have unique ion channel profiles.
    • Contractile cells lack spontaneous action potential generation.

    Ion Channels Involved

    • Fast sodium channels are essential for rapid depolarization.
    • L-type calcium channels contribute to the plateau phase.
    • Potassium channels are essential for repolarization.

    Excitation-Contraction Coupling

    • Calcium-induced calcium release (CICR) is the key mechanism.
    • Trigger calcium enters through L-type channels, triggering ryanodine receptors to release more calcium from the sarcoplasmic reticulum (SR).
    • Calcium binds to troponin, exposing actin binding sites.
    • Cross-bridge cycling occurs, generating force.
    • Calcium is pumped back into the SR and extracellular fluid for relaxation.

    Vascular Arrangement

    • Parallel vs. series circulation:
      • The parallel arrangement in the systemic circuit allows for equal blood quality to tissues.
      • The series arrangement in the pulmonary circuit ensures proper gas exchange.
      • Total resistance is lower in parallel systems, enhancing blood flow.
    • Sequence of blood vessels:
      • Blood flows from arteries to arterioles, then capillaries.
      • Venules collect blood before it returns through veins.

    Refractory Periods in Cardiac Muscle

    • Absolute Refractory Period (ARP):
      • No new action potential can be initiated.
      • Fast sodium channels are inactive during this phase.
      • Prevents tetanic contractions in cardiac muscle.
    • Relative Refractory Period (RRP):
      • Some sodium channels recover, allowing for potential for new action potentials.
      • Occurs as the cell membrane approaches full repolarization.
    • Importance:
      • Refractory periods ensure proper heart function.
      • Allow time for the heart to refill with blood.
      • Critical for preventing arrhythmias and maintaining cardiac output.

    The Cardiac Cycle

    • Consists of two phases: diastole (relaxation) and systole (contraction).
    • Diastole occupies about 2/3 of the cycle, while systole takes up 1/3.
    • Four phases:
      • Ventricular Filling (Diastole): Blood flows passively from atria to ventricles, followed by the atrial kick.
      • Isovolumetric Contraction (Systole): Ventricles contract with all valves closed, leading to pressure build-up.
      • Ejection (Systole): Ventricles eject blood into the aorta and pulmonary artery as valves open.
      • Isovolumetric Relaxation (Diastole): Ventricles relax with all valves closed, preparing for the next cycle.

    Stroke Volume (SV)

    • Defined as the volume of blood ejected from each ventricle per beat.
    • Calculated as SV = End-Diastolic Volume (EDV) - End-Systolic Volume (ESV).
    • Average stroke volume is approximately 70 mL at rest.

    Cardiac Output and Its Regulation

    • Cardiac output (CO) is the volume of blood ejected from each ventricle per minute.
    • CO = Heart Rate (HR) x Stroke Volume (SV).
    • Average values:
      • Resting CO ~ 5 L/min.
      • Maximum CO during exercise can reach 25-30 L/min.
    • Regulation of CO influenced by autonomic nervous system activity, blood volume, and heart contractility.
    • Most beta-adrenergic receptors in the heart are β1 receptors, which significantly regulate heart function.

    Ejection Fractions and Heart Failures

    • Types of heart failure:
      • Heart Failure with Preserved Ejection Fraction (HFpEF): Characterized by a stiff ventricle that struggles to relax, indicating diastolic dysfunction.
      • Heart Failure with Reduced Ejection Fraction (HFrEF): Traditionally recognized as heart failure, indicating systolic dysfunction.
    • Ejection fraction (EF) measures the heart's efficiency.
    • Typical EF values range from 55-70%, with lower values indicating potential heart failure.

    Autonomic Innervation of the Heart

    • Parasympathetic Effects:
      • Slow heart rate and weakens atrial contraction.
      • Reduces conduction speed through the AV node.
    • Sympathetic Effects:
      • Increases heart rate and enhances ventricular contraction strength.
      • Norepinephrine (NE) acts immediately, while epinephrine (Epi) supports NE effects.

    Control of Heart Rate

    • Resting state:
      • Parasympathetic input dominates, keeping heart rate around 70 bpm.
      • Sympathetic input is minimal.
    • Increased physical activity:
      • Decreases parasympathetic input and increases sympathetic input.
      • The intrinsic firing rate of SA nodal cells is 100 bpm, but resting heart rate is slower due to parasympathetic tone.

    Control of Stroke Volume

    • Preload and End-Diastolic Volume (EDV):
      • Stroke volume is influenced by changes in EDV, also known as preload.
      • Increased EDV enhances filament overlap, leading to stronger contraction.
    • Frank-Starling Law:
      • The Frank-Starling mechanism ensures matching output of the right and left ventricles.
      • Prevents blood from backing up into veins and capillaries, maintaining venous pressure.
    • Sympathetic Stimulation:
      • Increases stroke volume without changing EDV.
      • Norepinephrine and epinephrine enhance calcium availability, leading to stronger contractions.

    Afterload and Mean Arterial Pressure (MAP)

    • Increased afterload, or MAP, can decrease stroke volume, making it harder for ventricles to contract.
    • Afterload affects failing hearts significantly.

    Distribution of Cardiac Output

    • At Rest vs. During Exercise:
      • At rest, CO is distributed to maintain vital organ function.
      • During exercise, CO increases:
        • Heart rate rises linearly.
        • Stroke volume plateaus after a certain point.
    • Implications for Exercise:
      • Increased HR and SV support elevated CO during physical activity.

    Electrocardiogram (ECG/EKG)

    • The ECG is a diagnostic tool used to assess heart conditions.
    • Helps identify abnormal heart rates, arrhythmias, and myopathies.
    • Records the electrical activity of the heart, not the mechanical contraction.
    • Reflects the net sum of electrical potentials from cardiac muscle cells.
    • Measured using pairs of electrodes placed on the body surface.

    Cardiovascular System Components

    • The cardiovascular system primarily consists of the heart, blood, and blood vessels.

    • Heart: The heart serves as the biological pump that propels blood throughout the body.

      • Each heartbeat involves two phases:
        • Electrical (action potential)
        • Mechanical (contraction)
      • The left ventricle (LV) pumps oxygenated blood to the body, while the right ventricle (RV) pumps deoxygenated blood to the lungs.
        • The LV requires a thicker myocardium to generate higher pressure than the RV, as systemic circulation faces higher resistance than pulmonary circulation.

    • Blood: Blood comprises plasma (55-58% of total volume) and cellular components, including red blood cells, white blood cells (leukocytes), and platelets.

      • The average total blood volume is around 5.5 liters.

    • Blood Vessels: Blood vessels contribute significantly to blood movement and are categorized into pulmonary (lung) and systemic (body) circuits.

      • Systemic circulation is arranged in parallel, ensuring efficient and equal blood delivery to every organ.
      • Pulmonary circulation is in series, moving blood through the lungs in a sequential manner.

    Cardiovascular System Roles in Homeostasis

    • The cardiovascular system plays a vital role in maintaining homeostasis through:
      • Nutrient and Waste Transport: Efficiently delivers nutrients and removes waste products from cells.
      • Hormone and Signaling Molecule Distribution: Facilitates communication between different parts of the body, enabling rapid responses to physiological changes.
      • Temperature Regulation: Helps maintain body temperature by circulating warm blood to the extremities and dissipating heat.

    Pressure, Flow, and Resistance in the Cardiovascular System

    • Blood flow (F or Q) is determined by the pressure difference (ΔP) and resistance (R), following Ohm's Law: Flow = Pressure difference / Resistance.

    • The pressure gradient, not absolute pressure, drives blood flow.

    • Factors Affecting Resistance:

      • Vessel length (L)
      • Blood viscosity (η)
      • Vessel radius (r) - the most impactful factor (raised to the 4th power)

    • Impact of Vessel Radius: Minor changes in vessel radius can drastically alter resistance and blood flow.

      • This principle is essential for regulating blood flow to different organs.

    Heart Structure and Function

    • Heart Valves: Ensure unidirectional blood flow through the heart.

      • Atrioventricular (AV) Valves: Prevent backflow from ventricles to atria (right AV: tricuspid, left AV: bicuspid/mitral).
      • Semilunar (SL) Valves: Prevent backflow from arteries to ventricles (pulmonary and aortic semilunar valves).

    • Heart Tissue Layers:

      • Endocardium: Innermost layer, separating chambers from myocardium.
      • Myocardium: Thick layer of cardiac muscle.
      • Epicardium: Outer protective layer.
      • Pericardium: Fluid-filled sac surrounding the heart.

    Cardiac Muscle Cells and Electrical Activity

    • Cardiac Myocyte Characteristics:

      • Striated appearance
      • Primarily mononucleated
      • Branched ends for interconnection

    • Electrical Connections:

      • Gap junctions allow rapid electrical communication between cells.
      • Cells form a functional syncytium, enabling coordinated contraction.

    • Comparison with Skeletal and Smooth Muscle:

      • Similarities to Skeletal Muscle:
        • Presence of sarcomeres and striations
        • Contains troponin for calcium-mediated contraction
        • Presence of T-tubules
      • Similarities to Smooth Muscle:
        • Presence of pacemaker cells
        • Gap junctions forming a syncytium
        • Calcium entry from extracellular fluid
        • Modulation by the autonomic nervous system and hormones

    Cardiovascular System Regulation

    • Autonomic Nervous System Control:

      • Sympathetic: Increases heart rate and contractility.
      • Parasympathetic: Slows heart rate and weakens atrial contraction.

    • Receptor Types in Cardiovascular Regulation:

      • Cholinergic Receptors:
        • Nicotinic acetylcholine receptors (nAChR) at autonomic ganglia.
        • Muscarinic acetylcholine receptors (mAChR) on target tissues.
      • Adrenergic Receptors:
        • Beta (β) receptors: β1 and β2 are particularly important.
        • Alpha (α) receptors: Primarily α1.

    Conduction Pathway of the Heart

    • Sequence of Electrical Events:
      • Begins at the Sinoatrial (SA) node, the primary pacemaker.
      • The electrical impulse travels through the atria, causing them to contract.
      • The signal then reaches the atrioventricular (AV) node, where it is briefly delayed, allowing the ventricles to fill with blood.
      • The impulse then passes down the bundle of His, branching into Purkinje fibers that spread throughout the ventricles, triggering ventricular contraction.

    Refractory Periods in Cardiac Muscle

    • Absolute Refractory Period (ARP):
      • No new action potential can be initiated.
      • Fast Na+ channels are inactive during this phase.
      • Prevents tetanic contractions in cardiac muscle.
    • Relative Refractory Period (RRP):
      • Some Na+ channels recover, allowing weak potential for new action potentials.
      • Occurs as the cell membrane approaches full repolarization.
      • Enables rhythmic heart contractions.

    The Cardiac Cycle

    • The cardiac cycle consists of two primary phases:

      • Diastole (relaxation): Ventricles refill with blood (around two-thirds of the cycle).
      • Systole (contraction): Ventricles eject blood (around one-third of the cycle).

    • Four Phases of the Cardiac Cycle:

      • Ventricular Filling (Diastole): Blood flows passively from atria to ventricles, followed by atrial contraction (atrial kick).
      • Isovolumetric Contraction (Systole): Ventricles contract with all valves closed, increasing pressure inside.
      • Ejection (Systole): Ventricles pump blood into the aorta and pulmonary artery as valves open.
      • Isovolumetric Relaxation (Diastole): Ventricles relax with valves closed, preparing for the next cycle.

    • Stroke Volume (SV): The volume of blood ejected from each ventricle per beat.

      • Calculated as: SV = End-Diastolic Volume (EDV) - End-Systolic Volume (ESV).
      • Average stroke volume at rest is approximately 70 mL.

    Cardiac Output and Its Regulation

    • Cardiac Output (CO): The volume of blood ejected from each ventricle per minute.

      • Calculated as: CO = Heart Rate (HR) x Stroke Volume (SV).
      • Typical resting values: 70 beats/min and 70 mL/beat, resulting in approximately 5 L/min of cardiac output.
      • CO can reach 25-30 L/min during strenuous exercise.

    • Regulation of Cardiac Output:

      • Autonomic nervous system activity, blood volume, and heart contractility.
      • Most beta-adrenergic receptors in the heart are β1 receptors, significantly regulating heart function.

    Ejection Fractions and Heart Failures

    • Heart Failure with Preserved Ejection Fraction (HFpEF): Characterized by a stiff ventricle that struggles to relax, indicating diastolic dysfunction.

    • Heart Failure with Reduced Ejection Fraction (HFrEF): Traditionally recognized as heart failure, indicating systolic dysfunction.

    • Ejection Fraction (EF): Measures the heart's efficiency, typically calculated from the left ventricle.

      • Normal EF values range from 55-70%.
      • Lower EF values indicate potential heart failure.

    Autonomic Innervation of the Heart

    • Parasympathetic Effects:

      • Slows heart rate.
      • Weakens atrial contraction.
      • Reduces conduction speed through the AV node.

    • Sympathetic Effects:

      • Increases heart rate.
      • Enhances ventricular contraction strength.
      • Norepinephrine (NE) has immediate effects, while epinephrine (Epi) reinforces NE actions.

    Control of Heart Rate

    • Resting State: Parasympathetic input dominates, keeping heart rate around 70 bpm.
    • Increased Physical Activity: Parasympathetic input decreases, while sympathetic input increases.
    • The intrinsic firing rate of SA nodal cells is 100 bpm, but resting heart rate is slower due to parasympathetic tone.

    Control of Stroke Volume

    • Preload and End-Diastolic Volume (EDV): Stroke volume is influenced by changes in EDV (preload).

      • Increased EDV enhances filament overlap, leading to stronger contraction.

    • Frank-Starling Law: Ensures output from the right and left ventricles match, preventing blood backflow into veins and capillaries.

    • Sympathetic Stimulation: Increases stroke volume without changing EDV by enhancing calcium availability and leading to stronger contractions.

    • Afterload and Mean Arterial Pressure (MAP): Increased afterload (MAP) can decrease stroke volume.

      • Afterload has a significant impact on failing hearts.

    Distribution of Cardiac Output

    • At Rest vs. During Exercise:
      • At rest, cardiac output is distributed to maintain vital organ function.
      • During exercise, cardiac output increases, with heart rate rising linearly while stroke volume plateaus after a certain point.

    Electrocardiogram (ECG/EKG)

    • The ECG is a diagnostic tool used to assess heart conditions, including heart rate abnormalities, arrhythmias, and myopathies.
    • It records electrical activity of the heart using electrodes placed on the body surface.
    • The ECG represents the net sum of electrical potentials from cardiac muscle cells.

    Components of the Cardiovascular System

    • The heart is the biological pump that generates force to move blood through the body.
    • Each heartbeat involves two main events: electrical (action potential) and mechanical (contraction).
    • The left ventricle (LV) is thicker than the right ventricle (RV) to generate higher pressure for systemic circulation compared to the pulmonary circulation.
    • Blood is the transport medium, composed of plasma (55-58% of total volume) and cellular components.
    • The average total blood volume is 5.5 liters.
    • Hematocrit, the red blood cell volume, averages 42-45%.
    • The Buffy coat contains leukocytes and platelets.
    • The vasculature, or blood vessels, are not passive in blood movement.
    • The vasculature is divided into pulmonary and systemic circuits.
    • Blood vessels are arranged in parallel (systemic) and series (pulmonary) configurations.
    • Parallel arrangement allows for better regulation of blood flow and requires less pressure than the series arrangement.
    • Parallel arrangement ensures the same quality of blood to all tissues.

    Cardiovascular System Roles in Homeostasis

    • It delivers nutrients and removes waste products from cells, with most cells being within 10 um of a capillary for efficient exchange.
    • It facilitates communication between different parts of the body through hormone and signaling molecule distribution, enabling rapid responses to physiological changes.
    • It helps maintain body temperature through blood circulation, allowing for heat distribution and dissipation.

    Pressure, Flow, and Resistance in the Cardiovascular System

    • Flow or (Q) = Pressure difference (ΔP)/Resistance (R)
    • The pressure gradient drives blood flow, not the absolute pressure.
    • Factors affecting resistance: vessel length (L), blood viscosity (η), and vessel radius (r).
    • Vessel radius is the most significant factor in resistance, as it is raised to the 4th power.
    • Small changes in vessel radius can dramatically affect resistance and flow, making it a key mechanism for regulating blood flow.
    • The cardiac cycle consists of two main phases: diastole (relaxation) and systole (contraction).
    • Diastole occupies about 2/3 of the cycle, while systole takes up 1/3.

    Heart Structure and Function

    • The heart valves ensure one-way blood flow.
    • There are two types of valves: Atrioventricular (AV) and Semilunar (SL).
    • Atrioventricular valves (AV) include the right AV (tricuspid) and left AV (bicuspid/mitral) valves.
    • AV valves prevent backflow from ventricles to atria.
    • Semilunar valves (SL) include the pulmonary and aortic semilunar valves.
    • SL valves prevent backflow from arteries to ventricles.
    • The heart’s three tissue layers include the endocardium (innermost), myocardium (middle), and epicardium (outer).
    • The pericardium is a fluid-filled sac that surrounds the heart.

    Cardiac Muscle Cells and Electrical Activity

    • Cardiac myocytes are striated, mostly mononucleated, and have branched ends for interconnection.
    • Gap junctions allow rapid communication between cells, forming a functional syncytium for coordinated contraction.
    • Cardiac muscle is similar to skeletal muscle in its presence of sarcomeres, striations, troponin for calcium-mediated contraction, and T-tubules.
    • Cardiac muscle is similar to smooth muscle in its presence of pacemaker cells, gap junctions forming a syncytium, calcium entry from extracellular fluid, and modulation by the autonomic nervous system and hormones.

    Cardiovascular System Regulation

    • The autonomic nervous system controls heart rate and contractility through sympathetic and parasympathetic influences.
    • Cholinergic receptors include nicotinic acetylcholine receptors (nAChR) at autonomic ganglia and muscarinic acetylcholine receptors (mAChR) on target tissues.
    • Adrenergic receptors include beta (β) receptors (β1, β2) and alpha (α) receptors (α1).
    • These receptors are essential targets for therapeutic interventions in cardiovascular diseases.

    Conduction Pathway of the Heart

    • The electrical activity begins with the SA node, the primary pacemaker.
    • Atrial contractile cells facilitate the atrial kick.
    • The AV node introduces delays for proper timing.
    • The conduction system includes the Bundle of His, Bundle branches, and Purkinje fibers.
    • The Bundle of His conducts the impulse to the ventricles.
    • Bundle branches distribute signals to the ventricles.
    • Purkinje fibers ensure rapid contraction of ventricular muscle.
    • Cardiac muscle cells are connected via gap junctions, allowing for rapid communication and synchronization, forming a functional syncytium for coordinated heartbeats.
    • There are five phases of the action potential:
      • Phase 0: Rapid depolarization due to Na+ influx
      • Phase 1: Initial repolarization as Na+ channels close
      • Phase 2: Plateau phase maintained by Ca2+ influx
      • Phase 3: Rapid repolarization as Ca2+ channels close and K+ channels open
      • Phase 4: Resting membrane potential is established.
    • Nodal cells exhibit pacemaker potentials, conducting cells have unique ion channel profiles, and contractile cells lack spontaneous action potential generation.
    • Fast Na+ channels are crucial for rapid depolarization, L-type Ca2+ channels contribute to the plateau phase, and K+ channels are essential for repolarization.

    Excitation-Contraction Coupling

    • Calcium-induced calcium release (CICR) is the key mechanism.
    • Trigger Ca2+ enters through L-type channels, leading to the release of more Ca2+ from the SR via ryanodine receptors.
    • Calcium binds to troponin, exposing actin binding sites for cross-bridge cycling, generating force.
    • Calcium is pumped back into the SR and ECF for relaxation.
    • Calcium is essential for initiating contraction in cardiac muscle, regulating the strength and duration of muscle contraction, and involves both extracellular and intracellular calcium sources.
    • Parallel arrangement allows equal blood quality to all tissues, while series arrangement in the pulmonary circuit ensures proper gas exchange.
    • Total resistance is lower in parallel systems, enhancing blood flow.
    • Blood flows from arteries to arterioles, then capillaries, and then is collected by venules before returning through veins.

    Refractory Periods in Cardiac Muscle

    • The absolute refractory period (ARP) prevents the initiation of a new action potential, as fast Na+ channels are inactive during this phase.
    • The ARP prevents tetanic contractions in cardiac muscle.
    • The relative refractory period (RRP) occurs as the cell membrane approaches full repolarization, where some Na+ channels recover, allowing for the potential for new action potentials.
    • The RRP is important for maintaining rhythmic heart contractions.
    • Refractory periods ensure proper heart function, allow time for the heart to refill with blood, and are critical for preventing arrhythmias and maintaining cardiac output.

    The Cardiac Cycle

    • Four phases of the cardiac cycle include:
      • Ventricular Filling (Diastole): Blood flows passively from atria to ventricles, followed by the atrial kick.
      • Isovolumetric Contraction (Systole): Ventricles contract with all valves closed, leading to pressure build-up.
      • Ejection (Systole): Ventricles eject blood into the aorta and pulmonary artery as valves open.
      • Isovolumetric Relaxation (Diastole): Ventricles relax with all valves closed, preparing for the next cycle.
    • Stroke volume (SV) is the volume of blood ejected from each ventricle per beat, calculated as SV = End-Diastolic Volume (EDV) - End-Systolic Volume (ESV).
    • The average stroke volume is approximately 70 mL at rest.

    Cardiac Output and Its Regulation

    • Cardiac output (CO) is the volume of blood ejected from each ventricle per minute, calculated as CO = Heart Rate (HR) x Stroke Volume (SV).
    • Stroke volume is influenced by changes in EDV, otherwise known as preload.
    • Increased EDV enhances filament overlap, leading to stronger contractions.
    • The Frank-Starling mechanism ensures that the output of the right and left ventricles are matched, which prevents blood from backing up into veins and capillaries, maintaining venous pressure.
    • Sympathetic stimulation increases stroke volume without changing EDV, as norepinephrine and epinephrine enhance calcium availability, leading to stronger contractions.
    • Increased afterload, or MAP, can decrease stroke volume, making it harder for ventricles to contract.
    • Afterload affects failing hearts, where wall stress is significant.

    Distribution of Cardiac Output

    • At rest, cardiac output is distributed to maintain vital organ function.
    • During strenuous exercise, cardiac output increases with heart rate rising linearly while stroke volume plateaus after a certain point.
    • Increased heart rate and stroke volume work together to support elevated cardiac output during physical activity.

    Electrocardiogram (ECG/EKG)

    • The ECG is a diagnostic tool used to assess heart conditions, identifying abnormal heart rates, arrhythmias, and myopathies.
    • The ECG records the electrical activity of the heart, not the mechanical contraction.
    • The overall ECG reflects the net sum of electrical potentials from cardiac muscle cells, which is measured using pairs of electrodes placed on the body surface.

    Cardiovascular System Components

    • The Heart: A powerful biological pump responsible for moving blood throughout the body.
    • Heart Beat: Consists of two main events: electrical (action potential) and mechanical (contraction).
    • Left and Right Heart Sides: Differ in structure and function.
      • Left Ventricle (LV): Thicker myocardium for generating higher pressure for systemic circulation.
      • Right Ventricle (RV): Thinner myocardium for generating lower pressure for pulmonary circulation.
    • Blood: Transport medium composed of plasma (55-58% of total volume) and cellular components.
      • Total blood volume: Averages 5.5 liters.
      • Hematocrit (red blood cell volume): Averages 42-45%.
      • Buffy coat: Contains leukocytes and platelets.
    • Vasculature (Blood Vessels): Play an active role in blood movement.
      • Pulmonary and Systemic Circuits: Divided into two circuits for gas exchange and nutrient/waste transport.
      • Parallel and Series Configurations: Arranged in parallel (systemic) and series (pulmonary) configurations.
        • Parallel Arrangement: Allows for better regulation of blood flow and ensures the same quality of blood to all tissues.
        • Series Arrangement: Requires less pressure than parallel systems.

    Cardiovascular System Roles in Homeostasis

    • Nutrient and Waste Transport: Delivers nutrients and removes waste products from cells.

    The Heart’s Electrical Conduction System

    • Cardiac Conduction System: A specialized network of cells that coordinate heart contractions.
      • Sinoatrial (SA) Node: Known as the pacemaker, it generates electrical impulses that control heart rate.
        • Atrial Kick: Atrial contractile cells facilitate this process for efficient filling of ventricles.
      • Atrioventricular (AV) Node: Introduces a delay in impulse conduction for proper timing.
      • Bundle of His: Conducts impulse to the ventricles.
      • Bundle Branches: Distribute signals to the ventricles.
      • Purkinje Fibers: Ensure rapid contraction of ventricular muscle.
    • Importance of Electrical Connections:
      • Gap Junctions: Cardiac muscle cells are connected via these junctions.
      • Functional Syncytium: This connection ensures coordinated heartbeats by allowing for rapid communication and synchronization of cells.

    Cardiac Action Potentials

    • Phases of Action Potentials:

      • Phase 0: Rapid depolarization due to Na+ influx.
      • Phase 1: Initial repolarization as Na+ channels close.
      • Phase 2: Plateau phase maintained by Ca2+ influx.
      • Phase 3: Rapid repolarization as Ca2+ channels close and K+ channels open.
      • Phase 4: Resting membrane potential is established.

    • Differences Among Cell Types:

      • Nodal Cells: Exhibit pacemaker potentials.
      • Conducting Cells: Have unique ion channel profiles.
      • Contractile Cells: Lack spontaneous action potential generation.

    • Ion Channels Involved:

      • Fast Na+ channels: Crucial for rapid depolarization.
      • L-type Ca2+ channels: Contribute to the plateau phase.
      • K+ channels: Essential for repolarization.

    Excitation-Contraction Coupling

    • Calcium-induced Calcium Release (CICR): Key mechanism where trigger Ca2+ enters through L-type channels and activates ryanodine receptors to release more Ca2+ from the sarcoplasmic reticulum (SR).
    • Steps in Contraction:
      • Ca2+ binds to troponin, exposing actin binding sites.
      • Cross-bridge cycling occurs, generating force.
      • Ca2+ is pumped back into the SR and the extracellular fluid (ECF) for relaxation.
    • Role of Calcium: Essential for initiating and regulating the strength and duration of muscle contraction.

    The Cardiac Cycle

    • Cardiac Cycle: Composed of two main phases: diastole (relaxation) and systole (contraction).
      • Diastole (2/3 of cycle): Ventricular relaxation phase.
      • Systole (1/3 of cycle): Ventricular contraction phase.
    • Phases of the Cardiac Cycle:
      • Ventricular Filling (Diastole): Blood flows passively from atria to ventricles, followed by the atrial kick.
      • Isovolumetric Contraction (Systole): Ventricles begin to contract, but valves are still closed, leading to pressure buildup.
      • Ejection (Systole): As pressure increases, valves open, and blood is ejected into the aorta and pulmonary artery.
      • Isovolumetric Relaxation (Diastole): Ventricles relax, but valves remain closed, setting the stage for the next cycle.
    • Stroke Volume (SV):
      • Defined as the volume of blood ejected from each ventricle per beat.
      • Calculated as SV = End-Diastolic Volume (EDV) - End-Systolic Volume (ESV).
      • Average stroke volume is approximately 70 mL at rest.

    Cardiac Output and Its Regulation

    • Cardiac Output (CO): The volume of blood ejected from each ventricle per minute.
      • Calculated as CO = Heart Rate (HR) x Stroke Volume (SV).
    • Average values: Typical resting values are around 70 beats/min and 70 mL/beat, resulting in approximately 5 L/min of cardiac output.
    • CO during intense exercise: Can increase significantly, reaching 25-30 L/min.
    • Regulation of Cardiac Output: Influenced by autonomic nervous system activity, blood volume, and heart contractility.
      • β1 receptors in heart (most beta-adrenergic receptors): Significantly regulate heart function.

    Ejection Fractions and Heart Failures

    • Types of Heart Failure:
      • Heart Failure with Preserved Ejection Fraction (HFpEF): Characterized by diastolic dysfunction, where the left ventricle is stiff, making it difficult to relax.
      • Heart Failure with Reduced Ejection Fraction (HFrEF): Characterized by systolic dysfunction, where the left ventricle pumps less blood than normal.
    • Ejection Fraction (EF): Measures the heart’s pumping efficiency, typically calculated from the left ventricle.
      • Normal EF: 55-70%.
      • Lower EF: Indicates potential heart failure.

    Autonomic Innervation of the Heart

    • Parasympathetic Effects (Vagus Nerve):
      • Slows heart rate.
      • Weakens atrial contraction.
      • Reduces conduction speed through the AV node.
    • Sympathetic Effects:
      • Increases heart rate.
      • Increases ventricular contraction strength.
        • Norepinephrine (NE): Acts immediately.
        • Epinephrine (Epi): Supports NE effects.

    Control of Heart Rate

    • At Rest:
      • Parasympathetic dominates: Keeping heart rate around 70 bpm.
      • Minimal sympathetic input: Allows for a lower heart rate.
    • Physical Activity:
      • Decreased parasympathetic input.
      • Increased sympathetic input.
      • Intrinsic firing rate of SA nodal cells: 100 bpm.

    Control of Stroke Volume

    • Preload and End-Diastolic Volume (EDV): Stroke volume is influenced by changes in EDV, also known as Preload.
      • Increased EDV: Enhanced filament overlap leads to stronger contraction.
      • Frank-Starling Law: Ensures that the output of the right and left ventricles is matched.
    • Sympathetic Stimulation: Increases stroke volume without changing EDV.
      • Increased Ca2+ availability: Leads to stronger contractions.
    • Afterload and Mean Arterial Pressure (MAP): Increased afterload, or MAP, can decrease stroke volume, making it harder for ventricles to contract.

    Distribution of Cardiac Output

    • At Rest: Cardiac output is distributed to maintain vital organ function.
    • During Exercise: Cardiac output increases, with heart rate rising linearly, while stroke volume plateaus after a certain point.

    Electrocardiogram (ECG/EKG)

    • Definition and Purpose:
      • Diagnostic tool for assessing heart conditions: Helps identify abnormal heart rates, arrhythmias, and myopathies.
      • Measures electrical activity of the heart: Not the mechanical contraction.
    • Electrical Activity of the Heart:
      • ECG reflects the net sum of electrical potentials from cardiac muscle cells.
      • Measured using pairs of electrodes placed on the body surface.

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    Description

    This quiz covers the essential concepts of cardiac muscle and the electrical activity of the heart, including the role of atrial contractile cells and the conduction system. Learn about the phases of cardiac action potentials and how the heart maintains coordinated contractions. Test your knowledge on the structure and function of cardiac muscle cells and their electrical connections.

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