Cardiovascular SystemChapter 11

Conduction System• Intrinsic conduction system (nodal system)• Heart muscle cells contract, without nerve impulses!

Conduction System• Sinoatrial node = SA node (“pacemaker”) • right atrium

Conduction System• Atrioventricular node = AV node

• junction of the right atriumand right ventricle

Conduction System• Atrioventricular bundle = AV bundle (bundle of

His) • In the interventricular septum

• Bundle branches

• Purkinje fibers (ventricle wall muscles)

Heart Contractions• Contraction is initiated by the SA node• Impulse spreads to AV node, atria contract• Contraction is delayed• Passes through AV bundle, bundle branches and

Purkinje fibers• “wringing” contraction – begins at apex, moves

toward atria• Blood ejected

Cardiac Cycle• Atria contract simultaneously• Atria relax, then ventricles contract• Systole = contraction• Diastole = relaxation

Atrialcontraction

Mid-to-late diastole(ventricular filling)

Ventricular systole(atria in diastole)

Early diastole

Isovolumetriccontraction phase

Ventricularejection phase

Isovolumetricrelaxation

Ventricularfilling

Left atriumRight atrium

Left ventricleRight ventricle

• https://www.youtube.com/watch?v=T4x7-2HKtJ0

• https://www.youtube.com/watch?v=oHMmtqKgs50

• https://www.youtube.com/watch?v=qmpd82mpVO4

• Cardiac output (CO)• Amount of blood pumped by each side (ventricle) of the

heart in one minute

• Stroke volume (SV)• Volume of blood pumped by each ventricle in one

contraction (each heartbeat)

• Heart rate (HR) • Typically 75 beats per minute