Questions and Answers
What is the primary function of capillaries in the cardiovascular system?
Which statement about veins is true?
What does the equation $v = Q/A$ represent in the context of blood flow?
What is true about the structure of capillaries?
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Why is blood velocity lower in capillaries compared to arteries?
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Which of the following characteristics apply to venules?
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What does the ST segment in an electrocardiogram represent?
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How is the ST segment characterized in an electrocardiogram?
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What does the T wave of the electrocardiogram represent?
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What primarily determines the resting membrane potential of a cardiac cell?
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Which of the following occurs when there is an inward current in a cardiac cell?
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What is the sequence of events that leads to the T wave in an electrocardiogram?
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Which part of the electrocardiogram reflects isoelectric conditions?
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What does a positive charge brought into the cell signify for the cardiac membrane potential?
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Which phase of the cardiac cycle directly follows the ST segment?
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What occurs during the ST segment in terms of ventricular status?
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What is the intrinsic rate of phase 4 depolarization in the SA node compared to the AV node?
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Which ion conductance primarily causes the upstroke of the action potential in the SA node?
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During which phase of the action potential does repolarization occur?
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What effect does an increased conduction velocity through the AV node have on ventricular filling?
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Which of the following best describes the Absolute Refractory Period?
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What primarily causes initial repolarization in the ventricular action potential?
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What characterizes Phase 2 of the ventricular action potential?
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What does the variable Q represent in the context of blood flow?
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Which ion's conductance predominates during Phase 3 of the ventricular action potential?
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In the equation for blood flow, what does AP stand for?
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What is the relationship between blood flow and resistance as indicated by the equation?
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What occurs during Phase 4 of the ventricular action potential?
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What does TPR stand for in the context of blood flow?
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What is a defining feature of the sinoatrial (SA) node?
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How is cardiac output defined according to the given equations?
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How does the membrane potential behave during Phase 2 of the ventricular action potential?
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Which of the following equations is analogous to the equation for blood flow?
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During which phase does the K+ current significantly contribute to hyperpolarization?
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What does the term 'pressure gradient' refer to in cardiovascular physiology?
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What role does Ca2+ conductance play in Phase 2 of the ventricular action potential?
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What effect does a decrease in Ca2+ conductance have during Phase 3?
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Which phase of the ventricular action potential represents the resting membrane potential?
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What does the P wave represent in an electrocardiogram?
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Which interval can be affected by a heart block?
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What happens to the PR interval when the parasympathetic nervous system is stimulated?
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The QRS complex represents which of the following?
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What does the QT interval measure?
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An increased conduction velocity through the AV node results in what change to the PR interval?
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Which of the following does NOT influence the PR interval?
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What is buried within the QRS complex?
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Study Notes
Capillaries
- Largest total cross-sectional and surface area in the cardiovascular system.
- Composed of a single layer of endothelial cells, encapsulated by a basal lamina.
- Thin-walled structures facilitate exchange of nutrients, water, and gases.
Venules
- Formed from the merging of capillaries.
Veins
- Progressively merge into larger veins, culminating in the vena cava, which returns blood to the heart.
- Thin-walled and operate under low pressure.
- Contain the highest volume of blood in the cardiovascular system, known as the unstressed volume.
- Possess α-adrenergic receptors, which play a role in vascular tone.
Velocity of Blood Flow
- Expressed by the equation ( v = \frac{Q}{A} ) where ( v ) is velocity, ( Q ) is blood flow, and ( A ) is cross-sectional area.
- Blood velocity is inversely proportional to cross-sectional area, illustrated by higher velocity in the aorta compared to capillaries.
- Reduced velocity in capillaries enhances substance exchange across their walls.
Blood Flow
- Blood flow is defined by ( Q = \frac{AP}{R} ) where ( Q ) represents flow, ( AP ) is pressure gradient, and ( R ) is resistance.
- Flow is analogous to electric current, pressure to voltage, and resistance to resistance in electrical circuits.
Electrocardiogram (ECG) Features
- P wave: Represents atrial depolarization.
- PR interval: Measures conduction velocity through the AV node; increases under heart block and decreases with parasympathetic activation.
- QRS complex: Indicates ventricular depolarization.
- QT interval: Represents the entire period of ventricular depolarization and repolarization.
- ST segment: Isoelectric period indicating ventricular depolarization.
- T wave: Depicts repolarization of the ventricles.
Cardiac Action Potentials
- Resting membrane potential: Influenced by potassium conductance, approaches potassium equilibrium potential.
- Phase 0: Upstroke due to increased Ca2+ conductance leading to inward current.
- Phase 2: Plateau phase; characterized by a balance between inward Ca2+ current and outward K+ conductance.
- Phase 3: Repolarization with decreased Ca2+ conductance and increased K+ conductance.
- Phase 4: Resting state, where inward and outward currents are balanced, stabilizing at potassium equilibrium potential.
Sinoatrial (SA) Node
- Serves as the heart's primary pacemaker with unstable resting potential, dictating heart rhythm.
- Intrinsic rate of depolarization fastest in SA node, slower in AV node and His-Purkinje system.
Conduction Velocity
- Time required for excitation spread; higher inward current yields faster conduction.
- Fastest in the Purkinje system, slowest in AV node, critical for ensuring ventricular filling before contraction.
Refractory Periods
- Absolute Refractory Period (ARP): No action potential possible due to closed channels during most of the upstroke.
- Effective Refractory Period: Slightly longer than ARP where conducted action potential cannot occur.
Autonomic Nervous System Effects
- Chronotropic effects: Influence heart rate; negative effects reduce heart rate, while positive effects increase it.
- Dromotropic effects: Affect conduction velocity, primarily in the AV node; negative slows it down, positive speeds it up.
Negative Chronotropic and Dromotropic Effects
- Negative Chronotropic Effect: Slows heart rate by decreasing phase 4 depolarization rate in the SA node.
- Negative Dromotropic Effect: Slows conduction through AV node, increasing the PR interval.
Sympathetic Nervous System Effects
- Utilizes norepinephrine at β1 receptors to enhance heart rate and conduction velocity.
- Positive Chronotropic Effect: Increases heart rate by hastening phase 4 depolarization.
- Positive Dromotropic Effect: Rapid conduction through AV node, potentially compromising ventricular filling.
Myocardial Cell Structure
- Sarcomere: Contractile unit similar to those found in skeletal muscle, fundamental for myocardial contraction.
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Description
This quiz covers the autonomic effects of the sympathetic and parasympathetic systems on heart rate and conduction velocity. It examines different receptors involved and their specific impacts on cardiac function. Test your understanding of how these systems regulate heart activity.
