Cardiac Output and Heart Rate Regulation
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Questions and Answers

What is cardiac output (CO)?

The volume of blood pumped per minute by each ventricle.

What is stroke volume (SV)?

The amount of blood pumped per beat by each ventricle.

Cardiac output is calculated by multiplying stroke volume by ______.

heart rate

What is the approximate total blood volume in the human body?

<p>5.5 L</p> Signup and view all the answers

What is the primary controller of heart rate?

<p>The autonomic nervous system.</p> Signup and view all the answers

Without any neuronal influence, the SA node will drive the heart at a rate of its spontaneous activity.

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

What does the term "chronotropic effect" refer to?

<p>The effect of a substance or stimulus on heart rate.</p> Signup and view all the answers

How does the autonomic nervous system modify heart rate?

<p>By modifying the rate of spontaneous depolarization at the SA node.</p> Signup and view all the answers

What neurotransmitters stimulate the opening of pacemaker HCN channels in the SA node?

<p>Norepinephrine (NE) and epinephrine (Epi)</p> Signup and view all the answers

What is the effect of stimulating HCN channels in the SA node on heart rate?

<p>It depolarizes the SA node faster, leading to a greater heart rate.</p> Signup and view all the answers

Which neurotransmitter promotes the opening of K+ channels in the SA node?

<p>Acetylcholine (ACh)</p> Signup and view all the answers

What is the effect of opening K+ channels in the SA node on heart rate?

<p>It slows down depolarization and reduces heart rate.</p> Signup and view all the answers

What part of the medulla coordinates autonomic innervation to the heart?

<p>The cardiac control center.</p> Signup and view all the answers

Sympathetic endings in the atria and ventricles can stimulate an increase in the strength of contraction.

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

Which of the following are effects of sympathetic nerve activity on the heart?

<p>Increased conduction rate</p> Signup and view all the answers

What are the three variables that determine stroke volume?

<p>End diastolic volume (EDV), total peripheral resistance (TPR), and contractility.</p> Signup and view all the answers

What is the significance of end diastolic volume (EDV) in relation to stroke volume?

<p>EDV is the preload on the heart and is directly proportional to stroke volume.</p> Signup and view all the answers

What is total peripheral resistance (TPR)?

<p>It is the impedance blood flow encounters in the arteries.</p> Signup and view all the answers

Define contractility in the context of stroke volume.

<p>It is the strength of ventricular contraction.</p> Signup and view all the answers

What is the term for the workload on the heart prior to contraction?

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

What is the relationship between preload and stroke volume?

<p>Stroke volume is directly proportional to preload and contractility.</p> Signup and view all the answers

How does the strength of contraction relate to end diastolic volume (EDV)?

<p>They are directly proportional.</p> Signup and view all the answers

What is the term for the resistance the heart needs to overcome to eject blood from the ventricle?

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

What is the ejection fraction (EF) and how is it calculated?

<p>The EF is the percentage of blood that is ejected from the ventricle with each contraction. It is calculated by dividing stroke volume (SV) by end diastolic volume (EDV).</p> Signup and view all the answers

What is the significance of the Frank-Starling law of the heart?

<p>It states that the strength of ventricular contraction is directly proportional to the EDV.</p> Signup and view all the answers

What is the effect of sympathetic nerve stimulation on the heart muscle at the level of contractility?

<p>It increases contractility, leading to a more powerful contraction.</p> Signup and view all the answers

What is the term for the effect of a substance or stimulus on the heart's strength of contraction?

<p>Inotropic effect</p> Signup and view all the answers

How do NE and Epi produce a positive inotropic effect on the heart?

<p>They increase calcium levels (Ca2+) in sarcomeres, which is essential for muscle contraction.</p> Signup and view all the answers

What is venous return?

<p>The return of blood from the body back to the heart via the veins.</p> Signup and view all the answers

How does venous return control EDV, SV, and CO?

<p>Venous return regulates EDV, which directly influences SV and ultimately, CO.</p> Signup and view all the answers

What factors influence venous return?

<p>Venous pressure</p> Signup and view all the answers

What is the significance of the negative intrathoracic pressure during inhalation?

<p>It helps draw blood back to the heart, increasing venous return.</p> Signup and view all the answers

Explain why veins are called capacitance vessels?

<p>They can hold a large volume of blood and stretch easily without significant pressure changes.</p> Signup and view all the answers

Veins have a higher compliance compared to arteries.

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

What is the approximate percentage of blood volume held in systemic veins?

<p>60% to 70%</p> Signup and view all the answers

Study Notes

Cardiac Output, Blood Flow, and Blood Pressure

  • Cardiac output (CO) is the volume of blood pumped per minute by each ventricle
  • Stroke volume (SV) is the volume of blood pumped per beat by each ventricle
  • CO = SV x HR
  • Total blood volume is approximately 5.5 liters

Regulation of Cardiac Rate

  • The sinoatrial (SA) node initiates the heartbeat's rhythm in the absence of neuronal stimulus
  • Sympathetic and parasympathetic nervous system activity influence heart rate (chronotropic effect)
  • The autonomic innervation of the SA node regulates heart rate
  • Sympathetic and parasympathetic nerve fibers modulate spontaneous depolarization

Regulation of Cardiac Rate (continued)

  • Norepinephrine (NE) and epinephrine (Epi) stimulate the opening of pacemaker (HCN) channels
  • This accelerates SA node depolarization, increasing heart rate (HR)
  • Acetylcholine (ACh) promotes the opening of potassium (K+) channels
  • The resultant K+ outflow counteracts Na+ influx, slowing depolarization, and decreasing HR

Regulation of Cardiac Rate (continued)

  • The cardiac control center in the medulla coordinates the autonomic nervous system
  • Sympathetic nerve endings in atria and ventricles can increase the strength of contraction

Effects of Autonomic Nerve Activity on the Heart

  • Sympathetic: Increases the rate of diastolic depolarization, and increases cardiac rate. Increases conduction rate in the AV (atrioventricular) node. Increases strength of atrial muscle contraction and ventricular muscle contraction.
  • Parasympathetic: Decreases the rate of diastolic depolarization and thus decreases cardiac rate. Decreases AV node conduction rate. No significant effect on atrial or ventricular muscle.

Stroke Volume

  • Stroke volume (SV) is determined by three factors:
    • End-diastolic volume (EDV): the volume of blood in the ventricles at the end of diastole
    • Total peripheral resistance (TPR): impedance to blood flow in the arteries
    • Contractility: the strength of ventricular contraction

Regulation of Stroke Volume

  • EDV is the workload (preload) on the heart before contraction
  • Stroke volume (SV) is directly related to preload and contractility
  • Strength of contraction is directly related to EDV
  • Total peripheral resistance (afterload) impedes ejection from the ventricle
  • Ejection fraction is SV/EDV (normally 60%); a useful clinical diagnostic tool

Frank-Starling Law of the Heart

  • The strength of ventricular contraction directly correlates with EDV
  • This is an intrinsic property of the myocardium
  • Increased EDV stretches the myocardium, which results in stronger contraction
  • The law emphasizes the relationship between heart filling and contractility.

Frank-Starling Law of the Heart (continued)

  • The state of myocardial sarcomeres immediately before filling is characterized by actin overlap. Myosin interactions are reduced, leading to a weaker contraction
  • Increasing interaction of actin & myosin as ventricles fill leads to increased contractile force.

Extrinsic Control of Contractility

  • At any given EDV, strength of contraction is dependent upon the level of sympathetic-adrenal activity
  • Norepinephrine (NE) and epinephrine (Epi) increase heart rate and induce a positive inotropic effect (increasing the strength of contraction)
  • This is due to increased Ca2+ in the sarcomeres.

Venous Return

  • Venous return is the return to the heart of blood via veins
  • It controls end-diastolic volume (EDV), affecting stroke volume (SV), and cardiac output (CO)
  • Venous return depends on blood volume & venous pressure, vasoconstriction stemming from the sympathetic NS and skeletal muscle pump activity
  • Inhaling reduces venous pressure.

Venous Return (continued)

  • Veins carry most of the blood volume (approx. 70%) in the body, they are referred to as capacitance vessels. Walls are thin and thus highly compliant.

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Description

This quiz delves into the intricacies of cardiac output, blood flow, and blood pressure regulation. It highlights the roles of the sinoatrial node, autonomic nervous system, and the effects of neurotransmitters on heart rate. Test your understanding of these crucial cardiovascular concepts.

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