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3) Cardiovascular System: Heart - Cardiac Conduction

Structure and function of the heart.

Brandon Poe

on 9 October 2015

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Transcript of 3) Cardiovascular System: Heart - Cardiac Conduction

The Heart
From Scientific American:
From Free Patents Online:
Heart Anatomy: Chambers, Vessels, and Valves
Cardiac Conduction System
Cardiac Cycle
Cardiac Output
Cardiac output equals stroke volume times heart rate
CO = SV x HR

difference between resting and maximal cardiac output is called cardiac reserve
Regulation of Stroke Volume
1. Preload
2. Contractility
3. Afterload
degree of stretch of ventricles before contracting
Frank-Starling law of the heart
the greater the stretch - the greater the contraction (within limits)
stretch is due to blood in the ventricles at the end of diastole (EDV)
forcefulness of contraction of individual fibers
positive inotropic factors increase contractility

negative inotropic factors decrease contractility
direct consequence of greater Ca2+ influx
e.g. epinephrine, thyroxine
rising extracellular potassium
calcium channel blockers
pressure that must be exceeded before ejection begins
pressure at semilunar valves of large arteries
not under regulation, but negatively affected by chronic high BP
Regulation of Heart Rate
cardiovascular center of medulla (brain stem)
descending input to autonomic nervous sytem
sensory inputs:
movement as monitored by proprioceptors increase input to cardiovascular center
chemical changes in the blood, monitored by chemoreceptors
blood pressure changes , monitored by baroreceptors
Where is the first component of the cardiac conduction system located?

A) Right Atrium
B) Left Ventricle
C) Left Atrium
D) Right Ventricle
Is posting a test question to Yahoo!Answers cheating?
What does the word systole mean?

A) Blood pressure
B) Relaxation
C) Ventricle
D) Contraction
Which chamber of the heart receives deoxygenated blood from the body?

A) right atrium
B) right ventricle
C) left ventricle
D) left atrium
Which valve is found between the right atrium and ventricle?

A) pulmonary
B) aortic
C) tricuspid
D) mitral
What region of the heart contains the primary pacemaker cells?

A) Ventricular septum
B) Apex
C) Coronary sinus
D) Right atrium
Autorhythmic cells
Specialized cardiac muscle fibers that initiate and conduct electrical signals
SA node (intrinsic rate of 100/min)
AV node (intrinsic rate of 40-50/min)
Ventricular fibers (intrinsic rate of ~20/min)
Conduction Pathway
excitation begins at SA node
spreads through the atrial walls
internodal paths connect to AV node
signal flows to AV bundle
pathway branches into right and left bundle branches in interventricular septum
bundle branches turn up ventricular walls from apex and give rise to Purkinje fibers
Purkinje fibers connect to myocardium of ventricles
Stroke volume equals the amount of blood in ventricle during diastole (EDV) minus the amount of blood in ventricle after it has contracted (ESV)
80 ml/beat x 75 beats/min = 6000 ml/min
Location of the Heart
Step 1: The SA node depolarizes, initiating the
cardiac conduction pathway
Step 2: Depolarization spreads from the SA node throughout the atrial walls causing atrial contraction
Step 3: The AV node, in the atrial wall, is depolarized by the initial SA activity, and conducts that depolarization down through the AV bundle and the two bundle branches towards the apex of the heart
Step 4: Depolarization spreads along the bundle branches into the Purkinje fibers and through the rest of the ventricular walls, causing contraction of the ventricles
Step 5: Ventricles become fully depolarized and contracted
Step 6: Everything repolarizes and the heart is in a relaxed state between heart beats
Image source: https://en.wikipedia.org/wiki/Diastole#/media/File:Wiggers_Diagram.svg
Without input from the autonomic nervous system, what would the resting heart rate be?

A) 60 bpm
B) 75 bpm
C) 100 bpm
D) 140 bpm
All images (unless otherwise noted) are from CNX Anatomy & Physiology. OpenStax College. Sept 1, 2015. http://cnx.org/contents/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@7.28:1/Preface
Without input from the autonomic nervous system, what would the resting heart rate be?

A) 60 bpm
B) 75 bpm
C) 100 bpm
D) 140 bpm
Image source: https://commons.wikimedia.org/wiki/File:Gray968.png
Cardiac Conduction
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