Physiology Bride to Year 1 Flashcards
In what phase of ventricular action potential do you observe the mechanical contraction of the ventricular myocyte?
a) Phase 0
b) Phase 1
c) Phase 2
d) Phase 3
e) Phase 4
Ans = Phase 2
The ventricular action potential has different phases, each corresponding to specific ionic movements and electrical changes. Let’s go through each phase to understand where the mechanical contraction of the ventricular myocyte (heart muscle cell) is most likely to occur:
Phase 0_Rapid Depolarization: This phase is characterized by the rapid influx of sodium ions (Na+) into the cell, causing the cell’s interior to become more positive. This rapid change in voltage triggers the action potential but does not directly correspond to the mechanical contraction.
Phase 1_Rapid Depolarization: This phase is characterized by the rapid influx of sodium ions (Na+) into the cell, causing the cell’s interior to become more positive. This rapid change in voltage triggers the action potential but does not directly correspond to the mechanical contraction.
Phase 2_Plateau Phase: This phase is characterized by the balance between the influx of calcium ions (Ca2+) and the efflux of potassium ions (K+). The calcium influx is crucial because it triggers the release of more calcium from the sarcoplasmic reticulum inside the cell, which is essential for muscle contraction. This is the phase where mechanical contraction of the ventricular myocyte occurs, corresponding to the systolic phase of the cardiac cycle.
Phase 3_Repolarization: This phase is marked by the closure of calcium channels and the increased efflux of potassium, returning the cell to its resting membrane potential. The mechanical contraction is starting to end during this phase.
Phase 4_Resting Membrane Potential: This is the phase where the cell is at its resting state, with high permeability to potassium and low permeability to sodium and calcium. There is no mechanical contraction happening in this phase.
Based on this understanding, the mechanical contraction of the ventricular myocyte occurs during Phase 2, the Plateau Phase, of the ventricular action potential.
A physiologist was explaining steps in excitation-contraction coupling in cardiac myocytes and the sequence of events that occurs between the initiation of an action potential in cardiac muscle fiber and the resulting contraction and relaxation. Which step comes immediately after the release of calcium from SR?
a) Myosin heads bind to actin, leading to cross-bridge movement
b) Is re-sequestered by sarcoplasmic reticulum by the SERCA pump
c) The calcium would bind to the Troponin C
d) Calcium enters cell during depolarization and triggers release of calcium by terminal cisternae
e) Calcium is removed from Troponin C, and myosin unbinds from actin
Ans = C
The calcium would bind to the Troponin C.
Excitation-contraction coupling in cardiac myocytes involves a series of steps that link the electrical excitation of the cardiac muscle to its contraction and subsequent relaxation. Understanding what occurs immediately after the release of calcium from the sarcoplasmic reticulum (SR) can be clarified by examining each of the listed choices:
Myosin heads binds to actin, leading to cross-bridge movement: After calcium is released from the SR, it binds to troponin C on the actin filaments. This causes a conformational change that moves tropomyosin away from the active sites on actin, allowing the myosin heads to bind to actin. This binding is crucial step in the contractile process, leading to cross-bridge cycling and muscle contraction. However, this process occurs after calcium binds to troponin, not immediately after calcium is released from the SR.
Calcium is resequestered by sarcoplasmic reticulum by SERCA pump: This step is involved in the relaxation phase of muscle contraction. The SERCA (sarcoplasmic/ edoplasmic reticulum Ca2+ ATPase) pump actively transports calcium back into the SR, lowering cytosolic calcium levels and leading to muscle relaxation. This occurs after the contraction process, not immediately after calcium release from the SR.
The calcium would bind to the Troponin C: This is the correct step that comes immediately after the release of calcium from the SR. The released calcium ions bind to troponin C, which is part of the troponin complex on the thin filaments (actin). This binding is essential for initiating the subsequent steps leading to muscle contraction.
Calcium enters cell during depolarization and triggers release of calcium by terminal cisternae: This describes the process of calcium-induced calcium release, which occurs at the beginning of the excitation-contraction coupling process. Calcium entering the cell during depolarization (phase 2 action potential) triggers the release of more calcium from the SR. However, this is not the step that immediately follows the release of calcium from the SR.
Calcium is removed from TN-C, and myosin unbinds from actin: This step describes part of the muscle relaxation process. After contraction, calcium is removed from troponin C (TN-C), which allows tropomyosin to cover the active sites on actin again, leading to the detachment of myosin from actin. This step occurs at the end of the contraction cycle, not immediately after the release of calcium from the SR.
Therefore, the correct step that comes immediately after the release of calcium from the sarcoplasmic reticulum is “The calcium would bind to the Troponin C.”
The current through HCN channels, designated IF, plays a key role in the control of cardiac and neuronal rhythmicity and is called the pacemaker current. Which of the following ions are responsible for the pacemaker current?
a) Ca2+
b) Na+
c) K+
d) Cl-
Activation of beta-adrenergic receptors in the heart is normally associated with which of the following?
a) Decrease in the slope of phase 4 depolarization in SA nodal cells
b) Increase in conduction velocity through AV node
c) Inhibition of calcium-induced calcium release following depolarization in ventricular myocytes
d) Slower sequestration of calcium in the sarcoplasmic reticulum by the calcium-ATPase
e) Reduction in the rate of rise in ventricular pressure during isovolumic contraction
A 45-year-old patient underwent JVP recording. In the JVP tracings, C wave is due to
a) Atrial contraction
b) Tricuspid valve bulging into right atrium
c) Rapid filling of ventricle
d) Slow filling ventricle
e) Ventricular repolarization
The volume and pressure tracings of the left ventricle of the 20-year-old male are shown in the image. Isovolumetric contraction corresponds to which point?
Review the Ventricular Volume Curve !!!
The volume and pressure tracings of the left ventricle of the 20-year-old male are shown above. which of the following points corresponds with mitral valve opening?
Review The volume and pressure tracings of the left ventricle !!!
Which of the following is not true of the second (S2) heart sound?
a) Aortic valve closes before pulmonary valve
b) During Isovolumic relaxation
c) Wide splitting seen with expiration
d) High pitched sound
e) Closes when the pressure in ventricle is lower than the aorta
A 14-year-old male presents to his primary care physician with complaints of shortness of breath and easy fatigability when exercising for extended periods. He also reports that, when he exercises, his lower legs and feet turn a bluish-gray color. He cannot remember visiting a doctor since he was in elementary school. His vital signs are as follows: HR 72, BP 148/65, RR 14, and SpO2 97%. It is also noted that the newborn has bounding pulses and a continuous machine-like murmur at the left infraclavicular area. What is your most probable diagnosis?
a) Aortic stenosis
b) Mitral valve prolapse
c) Patent ductus arteriosus
d) Ventricular septal defect
e) Tricuspid stenosis
The mitral valve opens at which one of the following points in a given PV loop?
Review PV loop!!!
A 45-year-old has been treated with Digoxin, which is a positive inotropic agent, you see the following changes in the dashed line. Control is a solid line (before drug administration). Which of the following parameters will increase?
Review Pressure Loops!!!
A healthy man of average size is found to have a resting end-diastolic volume of 110 mL and ESV of 50mL. The calculated ejection fraction would be
a) 48%
b) 54%
c) 62%
d) 70%
A 45-year-old patient was hospitalized, the solid line indicates his pressure-volume loop. The change in the pressure-volume (dashed line) reflects due to which of the following
a) Abdominal Aorta clamping
b) Blood transfusion
c) Veno-dilation
d) Dobutamine infusion
e) Loss of myocardial mass
A 22-year-old man has a muscle blood flow of 220 ml/min and a hematocrit of 50. He has a mean arterial pressure of 120 mm Hg, a muscle venous pressure of 10 mm Hg, and a heart rate of 80 beats/min. Which of the following is the approximate vascular resistance in the muscle of this man?
a) 0.10 mm Hg/ml/min
b) 0.20 mm Hg/ml/min
c) 0.50 mm Hg/ml/min
d) 1.00 mm Hg/ml/min
If the diastolic pressure is 90 mm Hg and the systolic pressure is 110 mm Hg, the calculated mean arterial pressure would be
a) 110 mm Hg
b) 130 mm Hg
c) 120 mm Hg
d) 100 mm Hg
e) 97 mm Hg
