Regulation of Cardiac Output

Multiple Choice Questions (MCQs)

1. What does the Frank-Starling mechanism primarily regulate?
   a) Heart rate
   b) Stroke volume
   c) Peripheral resistance
   d) Venous return
   Answer: b) Stroke volume
2. What is the preload in cardiac physiology?
   a) The force the heart must overcome to eject blood
   b) The stretch on the heart before contraction, proportional to EDV
   c) The rate of venous return
   d) The duration of ventricular diastole
   Answer: b) The stretch on the heart before contraction, proportional to EDV
3. Which effect is associated with homeometric autoregulation?
   a) Bainbridge reflex
   b) Anrep effect
   c) Baroreceptor reflex
   d) Frank-Starling mechanism
   Answer: b) Anrep effect
4. What neurotransmitter is released by sympathetic cardioaccelerator nerve fibers?
   a) Acetylcholine
   b) Epinephrine
   c) Norepinephrine
   d) Dopamine
   Answer: c) Norepinephrine
5. What is the effect of strong vagal stimulation on the heart?
   a) Positive chronotropic and inotropic effects
   b) Temporary cardiac inhibition and possible ventricular escape
   c) Increased stroke volume
   d) Reduced venous return
   Answer: b) Temporary cardiac inhibition and possible ventricular escape
6. What is the Bainbridge reflex triggered by?
   a) Increased arterial pressure
   b) Increased venous return
   c) Elevated peripheral resistance
   d) High stroke volume
   Answer: b) Increased venous return
7. Which hormone has a positive chronotropic and inotropic effect on the heart?
   a) Insulin
   b) Thyroxine
   c) Acetylcholine
   d) Secretin
   Answer: b) Thyroxine
8. What is the effect of increased potassium (K⁺) on the heart?
   a) Increases heart rate
   b) Favors diastole by reducing contraction force
   c) Causes calcium rigor
   d) Increases contractility
   Answer: b) Favors diastole by reducing contraction force
9. Which reflex is mediated by baroreceptors in the carotid sinus and aortic arch?
   a) Bainbridge reflex
   b) Cardio-accelerator reflex
   c) Baroreceptor reflex
   d) Anrep effect
   Answer: c) Baroreceptor reflex
10. What is the primary function of catecholamines in cardiac regulation?
    a) Negative inotropic and chronotropic effects
    b) Positive chronotropic, inotropic, and dromotropic effects
    c) Decreasing cardiac output
    d) Enhancing vagal tone
    Answer: b) Positive chronotropic, inotropic, and dromotropic effects

Fill in the Blanks

1. The ________ mechanism allows the heart to regulate stroke volume based on EDV.
   Answer: Frank-Starling
2. The ________ reflex increases heart rate in response to increased venous return.
   Answer: Bainbridge
3. Strong vagal stimulation may lead to ________ escape if pacemaker activity shifts to ectopic foci.
   Answer: ventricular
4. The ________ effect increases contractile strength without altering fiber length.
   Answer: Anrep
5. ________ is the neurotransmitter released by parasympathetic cardioinhibitory nerve fibers.
   Answer: Acetylcholine

True or False

1. The Frank-Starling mechanism is an example of extrinsic regulation.
   Answer: False
2. Sympathetic stimulation increases heart rate and force of contraction via norepinephrine.
   Answer: True
3. The baroreceptor reflex reduces heart rate and blood pressure in response to increased arterial pressure.
   Answer: True
4. Calcium infusion causes diastolic relaxation.
   Answer: False
5. Increased preload leads to stronger myocardial contraction.
   Answer: True

Subjective Questions

1. Differentiate between preload and afterload in cardiac physiology.
   Answer:
   • Preload: Refers to the stretch on myocardial fibers before contraction, directly proportional to end-diastolic volume (EDV). Increased preload enhances stroke volume via the Frank-Starling mechanism.
   • Afterload: Refers to the force the heart must overcome to eject blood, often related to aortic pressure. Increased afterload raises end-systolic volume (ESV) and reduces stroke volume. Preload reflects the filling phase, while afterload reflects the ejection phase.
2. Explain how the autonomic nervous system regulates cardiac output.
   Answer:
   • Sympathetic Regulation:
     • Neurotransmitter: Norepinephrine.
     • Acts on β1 receptors in the SA node, AV node, and ventricles, increasing heart rate (positive chronotropic) and contractility (positive inotropic).
   • Parasympathetic Regulation:
     • Neurotransmitter: Acetylcholine (via vagus nerve).
     • Reduces heart rate (negative chronotropic) and contractility (negative inotropic) by delaying depolarization and slowing action potential conduction.
       These mechanisms ensure that cardiac output adjusts to meet metabolic demands in various physiological and pathological conditions.