Cardiac Physiology: Electromechanical Coupling
41 Questions
3 Views

Cardiac Physiology: Electromechanical Coupling

Created by
@WholesomeToad4877

Podcast Beta

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What initiates the release of calcium from the sarcoplasmic reticulum during cardiac electromechanical coupling?

  • Calcium ATPase pump activation
  • Opening of sodium channels
  • Increase in extracellular calcium concentration
  • Calcium-induced calcium release (CICR) (correct)

    • Which channel is primarily responsible for the influx of calcium that triggers CICR?

  • L-type calcium channels (Ca-L) (correct)
  • Potassium channels
  • Transient receptor potential channels
  • Voltage-gated sodium channels

    • What percentage of calcium from the sarcoplasmic reticulum is typically released during cardiac contraction?

  • 50% (correct)
  • 80%
  • 100%
  • 10%

    • What role do the pumps and exchangers in the sarcolemma play in cardiac muscle function?

    <p>Regulate ionic concentration and repolarization</p> Signup and view all the answers

    Which statement best describes the relationship between Ica-L and calcium release channels during cardiac excitation?

    <p>More Ica-L results in more clusters of calcium release channels opening</p> Signup and view all the answers

    How does inspiration affect systolic blood pressure during normal variations?

    <p>It results in a decrease in systolic blood pressure due to septum shift.</p> Signup and view all the answers

    What occurs as a result of increased intra-myocardial pressure during contraction?

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

    What impact does pulmonary artery hypertension (PTH) have on left ventricle stroke volume (SV)?

    <p>It decreases left ventricle stroke volume.</p> Signup and view all the answers

    What happens to the effective afterload if the stroke volume is reduced?

    <p>It increases.</p> Signup and view all the answers

    What is the relationship between right ventricular filling and stroke volume?

    <p>Increased right ventricular filling leads to an increase in stroke volume.</p> Signup and view all the answers

    What is the primary consequence of the compression of blood vessels toward the endocardial surface during systole?

    <p>Increased vulnerability to ischemia and injury</p> Signup and view all the answers

    During which phase does most of the subendocardial blood flow occur?

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

    What happens to arterial pulse pressure when arterial compliance decreases?

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

    Which action would most significantly increase blood flow in a vessel with constant perfusion pressure?

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

    Which statement about blood viscosity is true?

    <p>Viscosity can be defined as shear rate divided by shear stress</p> Signup and view all the answers

    What is the effect of reduced perfusion pressure on the endocardial region during contraction?

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

    What primarily results from a decrease in stroke volume?

    <p>Decreased cardiac output</p> Signup and view all the answers

    Which condition would most likely lead to an increase in endocardial ischemia?

    <p>Decreased perfusion pressure</p> Signup and view all the answers

    What is the effect of increased diameter of a blood vessel on shear stress at the vessel wall during laminar blood flow?

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

    What determines the percentage of fixed cardiac output that reaches a specific organ?

    <p>Organ absolute vascular resistance</p> Signup and view all the answers

    What is the primary outcome of increased sympathetic activation of myocyte b1 receptors?

    <p>Positive inotropic and positive chronotropic effects</p> Signup and view all the answers

    Where is shear stress greatest in a blood vessel?

    <p>At the wall of the vessel</p> Signup and view all the answers

    What effect does turbulent blood flow have on resistance?

    <p>It increases resistance to blood flow</p> Signup and view all the answers

    Which condition typically results in decreased blood flow and increased capillary pressure?

    <p>Arteriolar vasoconstriction</p> Signup and view all the answers

    How does shear stress vary with the viscosity of blood?

    <p>It is directly proportional to viscosity</p> Signup and view all the answers

    What happens to blood flow when the Reynolds number exceeds the critical threshold?

    <p>Blood flow becomes turbulent</p> Signup and view all the answers

    How does increased contractility affect stroke volume at fixed preload?

    <p>Increases stroke volume</p> Signup and view all the answers

    What is the relationship between contractility and cardiac function curves (CFC)?

    <p>Increasing contractility shifts CFC upward</p> Signup and view all the answers

    Which equation relates wall stress, pressure, and radius in the context of afterload?

    <p>s = P x (r / w)</p> Signup and view all the answers

    Which of the following factors increases the oxygen demand during isovolumic contraction?

    <p>Elevated pressure conditions</p> Signup and view all the answers

    What does the Tension Time Integral (TTI) represent?

    <p>The area under the pressure-time curve</p> Signup and view all the answers

    How does exhaling affect intra-thoracic pressure and afterload?

    <p>Increases intra-thoracic pressure, increasing afterload</p> Signup and view all the answers

    Which measure reflects both myocardial stress and time during contraction?

    <p>Tension Time Integral (TTI)</p> Signup and view all the answers

    What happens to stroke volume when there is decreased contractility at fixed preload?

    <p>Decreases stroke volume</p> Signup and view all the answers

    Which of the following does NOT increase energy demand during ventricular ejection?

    <p>Decreased wall thickness</p> Signup and view all the answers

    What is the effect of deep inspiration against a closed glottis on left ventricular pressure?

    <p>Increases left ventricular pressure significantly</p> Signup and view all the answers

    How does the double product relate to cardiac function?

    <p>It is calculated as mean arterial pressure times heart rate</p> Signup and view all the answers

    What occurs during isovolumic contraction in relation to oxygen demand?

    <p>Oxygen demand spikes due to high wall stress</p> Signup and view all the answers

    How does afterload affect the formula for wall stress?

    <p>It increases wall stress by increasing pressure in the formula</p> Signup and view all the answers

    What does an increase in preload do to stroke volume with constant contractility?

    <p>Increases stroke volume</p> Signup and view all the answers

    Which of the following best describes the effect of lowering the afterload on heart performance?

    <p>Reduces oxygen demand during contraction</p> Signup and view all the answers

    Study Notes

    Cardiac Muscle Electromechanical Coupling

    • Calcium influx through L-type calcium channels (Ica-L) triggers calcium-induced calcium release (CICR) from the sarcoplasmic reticulum (SR).
    • CICR is responsible for the majority of calcium release needed for muscle contraction, with Ica-L contributing only a small percentage.
    • The increased local calcium concentration activates the contractile machinery, resulting in muscle contraction.
    • Increased Ica-L results in a greater release of calcium from SR stores, leading to increased contractility.

    Stroke Volume

    • Stroke volume (SV) represents the amount of blood ejected from the ventricle during a single contraction.
    • Increased contractility leads to an increased SV at a fixed preload.
    • Decreased contractility leads to a decreased SV at a fixed preload.
    • The Frank-Starling (F-S) relationship describes the changes in SV as a function of preload.

    Ventricular Muscle's Load and Energy Demand

    • Wall stress, a major determinant of myocardial oxygen consumption, is proportional to the pressure (P) within the ventricle and the radius (r) of the ventricle, and inversely proportional to the thickness (w) of the ventricular wall.
    • High wall stress occurs during isovolumic contraction due to high pressure and radius.
    • Increased afterload in conditions like aortic stenosis or hypertension increases energy demand due to higher pressure.

    Measures of Ventricle Energy Demand

    • The area under the pressure-time curve reflects the total energy demand of the ventricle.
    • The tension-time integral (TTI) quantifies the energy demand by integrating wall stress over time.
    • Double product (MAP x HR) provides a clinically useful approximation of the ventricle's energy demand.

    Respiratory Determinants of Cardiac Function

    • Changes in intrathoracic pressure during respiration influence the afterload on the left ventricle.
    • During inspiration, decreased intrathoracic pressure can reduce ventricular transmural pressure, affecting SV.
    • This phenomenon can manifest as a slight decrease in systolic blood pressure during inspiration, referred to as pulsus paradoxus.

    Intra-Myocardial Pressures

    • Myocardial contraction increases ventricular pressure, leading to increased intra-myocardial pressure.
    • The higher pressure in the endocardium compresses subendocardial vessels during systole, limiting blood flow.
    • This explains the vulnerability of the endocardium to ischemia and injury during conditions of reduced perfusion pressure.
    • Subendocardial blood flow is primarily supplied during diastole.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Cardiac Electro-Mechanical Coupling and Determinants of Function PDF

    Description

    This quiz covers key concepts in cardiac muscle function, including electromechanical coupling, stroke volume, and the Frank-Starling relationship. Test your understanding of how calcium dynamics and contractility influence cardiac performance. Perfect for students studying cardiac physiology.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser