01/20/16

Question 1

Background of Cardiac Output

Answer 1

• Heart pumps blood around the body
• Left heart pumps oxygenated blood
• Right heart pumps deoxygenated blood

Question 2

Anatomy of the heart

Answer 2

Question 3

Anatomy of the heart; cartoon illustration

Answer 3

Question 4

The Cardiac Cycle

Answer 4

• Molecular/electrical/physiologicaleventsthat occur from the start of one heartbeat to the start of the next heartbeat
• Consists of 2 periods:
• Diastole:
  
  • relaxation,heart fills with blood
  • BP~80mmHg
• Systole:
  
  • contraction, heart ejects blood
  • BP~120mmHg

Question 5

Diastole

Answer 5

• Venous return fills atria
• AV valve opens
• ~75% blood flows directly into ventricles
• Atrial priming
  
  • pumps remaining 25% blood into ventricles
• AV valve closes

Question 6

Systole

Answer 6

• Ventricles fill with blood
• Increase in pressure
  
  • Isometric contraction
  • Aortic/pulmonary valves open
• Blood ejected
  
  • 70% fast, 30% slow
• Ventricles relax
• Aortic/pulmonary valves close

Question 7

What is cardiac output?

Answer 7

• Cardiac output=Stroke volume * Heart Rate
  
  • CO=SV*HR
• Stroke Volume
  
  • Blood volume ejected by ventricles/beat
• Heart Rate
  
  • # heart beats/min

Question 8

Calculating Cardiac Output

Answer 8

• Cardiac output (mL/min)=Stroke volume (mL/beat)*Heart rate (beats/min)
• Average resting heart rate:
  
  • ~70 beats/min
• Average resting stroke volume:
  
  • ~70 mL/beat
• Cardiact output=70*70=4900 mL/min
  
  • or ~5 L/min
• During exercise, CO increases 7 fold

Question 9

Preload and Afterload

Answer 9

• Determinants of stroke volume
• Preload
  
  • Tension of ventricular muscle before contraction
  • Determined by left ventricular end diastolic volume/pressure (LVED/LVEP)
• Afterload
  
  • Pressure against which ventricles pump blood
  • Determined by total peripheral resistance

Question 10

Excitiation-Contraction Coupling

Answer 10

• Generation of electrical impulses:
  
  • Sinus node
  • AV node
• Propogation of impulses:
  
  • Internodal pathways
  • Bachmann’s bundle
  • AV node, Bundle of His
  • Purkinje fibers

Question 11

Cardiac Electrophysiology

Answer 11

Question 12

Ion Channels Confirmational States

Answer 12

• Resting
  
  • Closed, can be opened
• Activated
  
  • Open, ions flowing
• Inactivated
  
  • Closed, can’t be opened

Question 13

Generation of Cardiac Rhythmicity

Answer 13

• Sinus (sinoatrial) node
  
  • “Pacemaker region”
  • Small specialized muscle
  • Located in right atrium
  • Controls heart rate
  • Origin of spontaneous action potential

Question 14

Spontaneous Action Potentials

Answer 14

• HCN channels
  
  • hyperpolarization cyclic nucleotide gated
• Phase 0:
  
  • Ca²⁺ enters: I_Ca-L
• Phase 3:
  
  • K⁺ exits: I_KS/I_KR
• Phase 4:
  
  • Na⁺ enters: I_f
  • Ca²⁺ enters: I_Ca-T/I_Ca-L
• Key:
  
  • L: long
  • S: short
  • T: transient
  • F: funny
  • KS: slow delayed rectifier
  • KR: rapid delayed rectifier

Question 15

Transmission of Cardiac Current

Answer 15

• Internodal pathways/Bachmann’s bundle
  
  • Spread current through atria
• AV node/Bundle of His
  
  • Electrically separate atria and ventricles
  • Delays current transmission to ventricles
  • Has spontaneous activity
    
    • Ectopic pacemaker
• Purkinje Fibers
  
  • Spreads currents through ventricles

Question 16

Transmission of Cardiac Impulses

Answer 16

Question 17

Non-spontaneous action potential

“cardiac action potential”

Answer 17

• Phase 0
  
  • Na⁺ enters: I_Na
• Phase 1
  
  • K⁺/Cl^- exits: I_to1/I_to2
• Phase 2
  
  • K⁺ exits: I_Ks
  • Ca²⁺ enters: I_Ca-L
• Phase 3
  
  • K⁺ exits: I_Ks/I_KR/I_K1
• Phase 4
  
  • Resting membrane potential

Question 18

Cardiomyocyte Contraction

Answer 18

• Increase [Ca²⁺]_i through L-type Ca²⁺ channels
• Ca²⁺ spread through transverse T-tubules
• Ca²⁺ opens rynodine receptors on sarcoplasmic reticulum
  
  • Calcium induced calcium release
• Ca²⁺ binds troponin-C
• Releases tropomyosin from actin
• Increases actin-myosin cross-bridging

Question 19

Channels and Proteins in Cardiomyocyte Contraction: Illustration

Answer 19

Question 20

Troponin and Myosin Chains in Cardiomyocyte Contraction: Illustration

Answer 20

Question 21

Thick/Thin Filament in Cardiomyocyte Contraction: Illustration

Answer 21

Question 22

Factors affecting Cardiac Output

Answer 22

• Frank-Starling Mechanism
• Autonomics
  
  • Sympathetic nervous system
  • Parasympathetic nervous system
• Renin-Angiotensin-Aldosterone System

Question 23

Frank-Starling Mechanism

Answer 23

• “Within physiological limits, the heart pumps all the blood that it receives without allowing excessing damming of blood in the veins”
• Increase in venous return
  
  • Cardiomyocyte contractility
• Increase stroke volume

Question 24

Autonomic Regulation of Cardiac Output

Answer 24

• Parasympathetic Nervous System
  
  • Decrease HR and SV
  • Dominant at rest
• Sympathetic Nervous System
  
  • Increase HR and SV
  • Dominant during exercise/stress

Question 25

Autonomic Nervous System: Innervation Illustration

Answer 25

Question 26

Parasympathetic Effects

Answer 26

* Vagal nerves release acetylcholine * SA and AV nodes * Acetylcholine stimulates M2-muscarinic receptors * Increase K⁺ channel opening * Decrease sinoatrial node rhythm * Decrease AV node transmission

Question 27

Sympathetic Effects

Answer 27

* Sympathetic nerves release norepinephrine throughout heart * Stimulates Beta-1-adrenergic receptors * Increase Ca/Na channel opening * Increase SA node rhythm * Increase AV node transmission * Increase force of atrial/ventricular contraction

Question 28

Autonomic nervous system regulation of spontaneous action potential

Answer 28

* PSNS→rest * Decrease AP frequency * Increase phase 4 duration * Decrease HR→Decrease CO * SNS→excercise, stress * Increase AP frequency * Decrease phase 4 duration * Increase HR→Increase CO

Question 29

Baroreceptor Reflex

Answer 29

* Rapid, fine control of CVS * Sensory baroreceptors * Carotid sinus/aortic arch * Detect BP changes * Increase BP * Increase PSNS activity * Decrease CO * Decrease BP * Increase NS activity * Increase CO

Question 30

Renin-Angiotensin-Aldosterone System

Answer 30

* Decrease BP in kidney nephron macula densa * Renin secreted into circulation * Renin→angiotensin to angiotensin I * Angiotensin converting enzyme (ACE) * angiotensin-I to angiotensin-II * Increase aldosterone * Increase plasma volume * Increase BP * Increase CO