PHYSIOLOGY OF THE HEART

 

 I  Cardiac Cycle

            A.  Definition:  systole, diastole

            B.  “Two-step” pumping

            C.  Coordination of two-step pumping               

                        1.  intrinsic conduction system             

                                    a.  SA node

                                    b.  AV node                   

                                    c.  Bundle of His, bundle branches            

                                    d.  Purkinje fibers                            (animation of intrinsic conduction system)

                        2.  spread of AP across heart                       

                                    a.  pacemakers                                       

                                                1.  varying conduction rates

                                                            a.  AV nodal delay

                                    b.  gap junctions                   

                                            

            D.  Cardiac action potential

                        1.  characteristics

                                    a.  rmp ---> threshold

                                    b.  depolarization

                                    c.  plateau, slow Ca++ influx

                                    d.  repolarization

                                    e.  time (250msec);  refractory period

                        2.  significance of Ca+ plateau and refractory period

 

                                       

II   Cardiac Output

            A.  Definition

                        1.  stroke volume (SV) x heart rate (HR) = cardiac output (CO)

                        2.  average CO, variations

            B.  Regulation of cardiac output

                        1.  factors affecting stroke volume

                                    a.  preload (EDV)

                                                1.  length of diastole

                                                2.  venous return

                                                3.  Frank-Starling Law of the Heart

                                    b.  contractility

                                                1.  sympathetic nervous system effects

                                                2.  endocrine effects

                                    c.  afterload

                                                1.  blood pressure effects          

                        2.  heart failure

                                    a.  definition

                                    b.  back failure

                                                1.  left ventricular failure effects

                                                2.  right ventricular failure effects

                                    c.  front failure

                        3.  factors affecting heart rate

                                    a.  intrinsic regulation

                                    b.  extrinsic regulation

                                                1.  neural, autonomic nervous system

                                                            a.  parasympathetic:  vagus nerve

                                                                        1.  ACh; hyperpolarization of SA and AV nodes

                                                            b.  sympathetic:  cardiac nerves

                                                                        1.  epinephrine; depolarization of nodes and heart

                                                                             muscle

                                                            c.  balance between parasympathetic and sympathetic    animation sympathetic vs parasympathetic

                                                2.  chemical                                                   

                                                            a.  hormones from adrenal medulla

                                                            b.  thyroxine

                                                            c.  ions:  Na+   K+   Ca++

                                                            d.  oxygen

                                                            e.  pH

                                                3.  other factors

                                                           

III   Electrocardiogram  (EKG)

 

                          

                    Sir Thomas Lewis mastered the technology of the electrocardiogram

                                  in 1912, a device for recording the activity of the heart
                                            (Cambridge Illustrated History of Medicine, 1996)
      

                          

          A.  Definition

                        1.  electrical vs. mechanical

            B.  Components                                       

                        1.  P wave;  atrial depolarization  

                                    a.  PR segment;  nodal delay

                        2.  QRS complex;  ventricular depolarization

                                    a.  ST segment

                        3.  T wave;  ventricular repolarization

                                    a.  TP interval

                        4.  atrial repolarization? ;  wave comparisons       

                        5.  concurrent mechanical events                           

            C.  Readings

                        1.  heart rate

                                    a.  tachycardia,

                                    b.  bradycardia

                                    c.  flutter  

                        2.  wave size

                        3.  arrhythmias

                                    a.  fibrillation

                                    b.  heart blocks 

                                                1.  1st degree

                                                2.  2nd degree

                                                3.  complete                        (electrocardiogram game)

                                                                                          

                                                                                              Practice EKG strips

                                                                         

 

 

when you complete this unit you should be able to:

    -  describe the events and movement of the blood during one cardiac cycle

    -  define a syncytium and explain the role of gap junctions between cells of the cardiac muscle

    -  list the four areas of the intrinsic conduction system and explain the general role of this system in the heart

    -  explain the role of the SA node and why it is the "pacemaker"

    -  explain the effect of the AV nodal delay

    -  explain the need for AP speed through the Purkinje fibers 

    -  draw a graph of a cardiac action potential plotting voltage versus time, label the phases, and the ion movements during each phase

    -  explain why cardiac muscle cannot experience tetanus and why this is good

    -  compare a cardiac action potential and a neural action potential

    -  define cardiac output using stroke volume and heart rate and calculate cardiac output in various situations

    -  define "preload" (end-diastolic volume), ways to increase the preload, and how the preload effects the cardiac output

    -  state the Frank-Starling law of the heart

    -  define afterload and explain how it effects the cardiac output

    -  define heart failure and compare the symptoms of left heart failure and right heart failure

    -  distinguish between intrinsic and extrinsic regulation of heart rate

    -  explain the different ways the sympathetic nervous system is able to effect cardiac output 

    -  explain how the parasympathetic nerves (vagus) and sympathetic nerves are able to effect the heart rate  

    -  define "vagal" tone

    -  discuss ways to effect cardiac output

    -  explain what the EKG reveals about the heart

    -  draw and label the waves of a normal EKG, explaining what each wave represents

    -  explain what is occurring in the intrinsic conduction system during the phases of the EKG

    -  explain what is occurring mechanically (diastole and systole) during the phases of the EKG

    -  define tachycardia, bradycardia, flutter and fibrillation

    -  explain "heart block"  and distinguish between 1st degree, 2nd degree, and complete heart block

 

   

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