CARDIOVASCULAR SYSTEM P. 347-352

Heart Actions

CARDIAC CYCLE

One complete heartbeat Atrial contraction, ventricular relaxation Atrial relaxation, ventricular contraction

Pressure within heart Rises and falls as chambers fill and empty

Atrial or Ventricular Contraction (Systole) Pressure

Pressure increases sharply

Atrial or Ventricular Relaxation Diastole Pressure

Pressure goes back down

AV Valves are opening and closing during pressure changes

HEART SOUNDS

Vibrations in heart tissue produce opening and closing of valves

Heard as LubDup through stethoscope Lub

Heard during ventricular contraction (AV valves are closing)

Dup Heard during ventricular relaxation (pulmonary and aortic

valves are shutting)

MurMur Abnormal sound

Usually occurs when heart valves don’t properly close causing blood to leak through

CARDIAC MUSCLE FIBERS

Act like skeletal muscles but connect to a network of sending impulses to contract all as a unit.

Functional Syncytium Mass of merging cells that act as a unit

CARDIAC CONDUCTION SYSTEM

Coordinates events of cardiac cycle Sinoatrial Node (SA Node)

Small mass of elongated specialized cardiac muscle tissue

Cells reach threshold on own and membranes contract one another

Initiate impulses that spread into the surrounding myocardium and stimulate cardiac muscle fiber to contract

Rhythmic activity 70-80 impulses/min. (Pulse) Pacemaker (Rhythmic contracting)

ATRIOVENTRICULAR NODE (AV NODE) Located in septum Receives slow impulse After received impulse AV node sends it on to

AV Bundle Purkinje Fibers

Allow transmission of impulse for contraction of the ventricles and pushes blood on out to aorta

ECG/EKG…ELECTROCADIOGRAM

Recording of the electrical changes in the myocardium during cardiac cycle

Deflections = waves on paper Polarization and repolarization causes pen to

move

P QRS T WAVES P wave

Depolarization, contraction of atriums QRS Complex

Waves correspond to depolarization of ventriular fibers that contract ventricles, atriums relax, ventricles contract

T wave Ventricles relax, pattern ends

P-R Interval Wave travels through AV node, AV bundles, bundle branches and

purkinje fibers S-T Segment

Time for complete excitation of ventricles Q-T Interval

Time required for complete excitation and recovery of ventricles T-P Interlude

Time from completion of ventricular repolarization to next atrial excitation

REGULATION OF CARDIAC CYCLE

Read p. 356

Arrhythmia Abnormal heart rhythm http://www.youtube.com/watch?v=xw4nDMgTOr

w

REVIEW

Describe the pressure changes in the atria and ventricles during a cardiac cycle.

What causes heart sounds? What is a functional syncytium? How is a cardiac impulse imitated? How is a cardiac impulse transmitted from

the right atrium to the other heart chambers?