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Questions and Answers
What initiates the release of calcium from the sarcoplasmic reticulum during cardiac electromechanical coupling?
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?
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?
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?
What role do the pumps and exchangers in the sarcolemma play in cardiac muscle function?
Which statement best describes the relationship between Ica-L and calcium release channels during cardiac excitation?
Which statement best describes the relationship between Ica-L and calcium release channels during cardiac excitation?
How does inspiration affect systolic blood pressure during normal variations?
How does inspiration affect systolic blood pressure during normal variations?
What occurs as a result of increased intra-myocardial pressure during contraction?
What occurs as a result of increased intra-myocardial pressure during contraction?
What impact does pulmonary artery hypertension (PTH) have on left ventricle stroke volume (SV)?
What impact does pulmonary artery hypertension (PTH) have on left ventricle stroke volume (SV)?
What happens to the effective afterload if the stroke volume is reduced?
What happens to the effective afterload if the stroke volume is reduced?
What is the relationship between right ventricular filling and stroke volume?
What is the relationship between right ventricular filling and stroke volume?
What is the primary consequence of the compression of blood vessels toward the endocardial surface during systole?
What is the primary consequence of the compression of blood vessels toward the endocardial surface during systole?
During which phase does most of the subendocardial blood flow occur?
During which phase does most of the subendocardial blood flow occur?
What happens to arterial pulse pressure when arterial compliance decreases?
What happens to arterial pulse pressure when arterial compliance decreases?
Which action would most significantly increase blood flow in a vessel with constant perfusion pressure?
Which action would most significantly increase blood flow in a vessel with constant perfusion pressure?
Which statement about blood viscosity is true?
Which statement about blood viscosity is true?
What is the effect of reduced perfusion pressure on the endocardial region during contraction?
What is the effect of reduced perfusion pressure on the endocardial region during contraction?
What primarily results from a decrease in stroke volume?
What primarily results from a decrease in stroke volume?
Which condition would most likely lead to an increase in endocardial ischemia?
Which condition would most likely lead to an increase in endocardial ischemia?
What is the effect of increased diameter of a blood vessel on shear stress at the vessel wall during laminar blood flow?
What is the effect of increased diameter of a blood vessel on shear stress at the vessel wall during laminar blood flow?
What determines the percentage of fixed cardiac output that reaches a specific organ?
What determines the percentage of fixed cardiac output that reaches a specific organ?
What is the primary outcome of increased sympathetic activation of myocyte b1 receptors?
What is the primary outcome of increased sympathetic activation of myocyte b1 receptors?
Where is shear stress greatest in a blood vessel?
Where is shear stress greatest in a blood vessel?
What effect does turbulent blood flow have on resistance?
What effect does turbulent blood flow have on resistance?
Which condition typically results in decreased blood flow and increased capillary pressure?
Which condition typically results in decreased blood flow and increased capillary pressure?
How does shear stress vary with the viscosity of blood?
How does shear stress vary with the viscosity of blood?
What happens to blood flow when the Reynolds number exceeds the critical threshold?
What happens to blood flow when the Reynolds number exceeds the critical threshold?
How does increased contractility affect stroke volume at fixed preload?
How does increased contractility affect stroke volume at fixed preload?
What is the relationship between contractility and cardiac function curves (CFC)?
What is the relationship between contractility and cardiac function curves (CFC)?
Which equation relates wall stress, pressure, and radius in the context of afterload?
Which equation relates wall stress, pressure, and radius in the context of afterload?
Which of the following factors increases the oxygen demand during isovolumic contraction?
Which of the following factors increases the oxygen demand during isovolumic contraction?
What does the Tension Time Integral (TTI) represent?
What does the Tension Time Integral (TTI) represent?
How does exhaling affect intra-thoracic pressure and afterload?
How does exhaling affect intra-thoracic pressure and afterload?
Which measure reflects both myocardial stress and time during contraction?
Which measure reflects both myocardial stress and time during contraction?
What happens to stroke volume when there is decreased contractility at fixed preload?
What happens to stroke volume when there is decreased contractility at fixed preload?
Which of the following does NOT increase energy demand during ventricular ejection?
Which of the following does NOT increase energy demand during ventricular ejection?
What is the effect of deep inspiration against a closed glottis on left ventricular pressure?
What is the effect of deep inspiration against a closed glottis on left ventricular pressure?
How does the double product relate to cardiac function?
How does the double product relate to cardiac function?
What occurs during isovolumic contraction in relation to oxygen demand?
What occurs during isovolumic contraction in relation to oxygen demand?
How does afterload affect the formula for wall stress?
How does afterload affect the formula for wall stress?
What does an increase in preload do to stroke volume with constant contractility?
What does an increase in preload do to stroke volume with constant contractility?
Which of the following best describes the effect of lowering the afterload on heart performance?
Which of the following best describes the effect of lowering the afterload on heart performance?
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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.
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