THURSDAY'S NOTES

6.  Heart Valves (See p. 375 Fig.15-4)

     a. Valves:  between each chamber to prevent blood from flowing backward; open & close to response to        pressure changes as heart contracts & relaxes

     b.  Atrioventricular (AV) valves:  valves between atria & ventricles

     c.  Tricuspid Valve:  between right atrium & ventricle; has 3 cusps

     d.  Chordae tendineae:  tendon-like cords that connect the pointed ends of the valves to cardiac muscle (papillary muscles) on the inner surface of the ventricles

     e.  Bicuspid (mitral) Valve:  valve between left atrium & ventricle; has 2 cusps

     f.  Semilunar Valves:  near origin of the pulmonary trunk & aorta; prevents blood from flowing back into heart  

     g.  Pulmonary Valve:  where pulmonary trunk leaves the right ventricle

     h.  Aortic Valve:  at opening between the left ventricle & the aorta

     i.  Stenosis:  failure of a heart valve to fully open

                -Mitral Stenosis:  congenital defect or scar that causes narrowing of mitral valve.

    j.  Insufficiency or Incompetence:  failure of a valve to close completely

                -Mitral Insufficiency:  allows backflow of blood from left ventricle into left atrium

C.  Blood Flow

  1.  Blood flows from areas of high to low pressure.

  2.  Cardiopulmonary Resuscitation (CPR):  chest compressions w/ artificial ventilation of lungs used to force blood out of the heart & into circulation until the heart can be restarted

   3.  Coronary (Cardiac) Circulation:  flow of blood thru vessels in the myoccardium

        a.  Left & Right  Coronary Arteries:  major coronary vessels that branch off the aorta

        b.  Coronary Sinus:  large vein that collects CO2 & waste from myocardium & delivers to right atrium

   4.  Anastomoses:  connections between arteries supplying the same region

        a.  alternate routes for blood to reach an organ or tissue

         b.  myocardium contains many, so heart can get oxygen even if 1 coronary artery is partially blocked

 D.  Conduction System of the Heart (See p.378 Fig.15.6)

    1.  1% of the cardiac muscle fibers generate an action potential in a rhythmic pattern.

    2.  Pacemaker:  cardiac cells set the rhythm for the heart

     3.  Conduction System:  action potential route throughout the heart muscle; synchronizes chamber contractions  

            a.  Sinoatrial (SA) node:  action potential begins in the right atrial wall & conducts thru both atria

            b.  Atrioventricular (AV) node:  in the interatrial septum where action potential slows so atria can       empty its blood into the ventricles

            c.  Atrioventricular (AV) bundle:  in interventricular septum where action potential moves from atria to ventricles

            d.  Right & Left Bundle branches:  action potential travels thru interventricular septum toward heart’s apex

            e.  Purkinje fibers:  rapidly conducts action potential to apex & toward the rest of the ventricular myocardium; allowing the ventricle to contract a fraction after the atria

 FRIDAY'S NOTES

  4.  SA node initiates action potentials about 100 times/ minute; acts as the pacemaker

           a.  Hormones & neutrotransmitters speed or slow the pace.

  5.  Ectopic Pacemaker:  site other than SA node becomes the pacemaker

           a.  can operate only occasionally or cause irregular heartbeat

           b.  triggers:  caffeine, nicotine, electrolyte imbalance, hypoxia   

  6.  Artificial Pacemaker:  device that sends small electrical charges to heart; can restore an irregular rhythm

 E.  Electrocardiogram (ECG):  recording of electrical changes accompanying a heartbeat

       1.  3 distinct waves:

             a.  P wave:  small upward wave; represents atrial depolarization which causes contraction of atrium

             b.  QRS complex:  represents ventricle depolarization which causes ventricle contraction

             c.  T wave:  dome-shaped deflection; shows ventricular repolarization before ventricles relax

        2.  Variation in size & length of ECG waves are used to diagnose abnormal cardiac rhythms & conduction patterns

              a.  ECG also reveals presence of living fetus

  F.  Cardiac Cycle:  all the events associated w/ 1 heartbeat

         1.  Systole:  contraction phase

         2.  Diastole:  relaxation phase

         3.  3 parts of the Cardiac Cycle

             a.  Relaxation Period:  at the end of the cardiac cycle when ventricle relax & all 4 chambers are in diastole; ventricle pressure so AV valves open & ventricular filling begins; about 75% full (T wave)

             b.  Atrial  Systole:  atria contracts forcing the last 25% of the blood into the ventricles (AV valves are still open & semilumar valves are closed) (P wave)

             c.  Ventricular Systole:  ventricles contracts pushing blood against AV valves, forcing them shut & causing both semilunar valves open to eject blood from pulmonary trunk & aorta until the ventricles relax (cardiac cycle restarts) (QRS complex)

   G.  Heart Sounds

        1.  Heart sounds come from blood flow turbulence when valves close, not from heart contraction.

        2.  Lubb:  1^st sound; AV valves closing after ventricular systole begins

        3.  Dupp:  2^nd sound; short, sharp sound of semilunar valves closing at the end of the ventricular systole

        4.  Pause: during relaxation period