Circulatory System How does the heart work?

Heart beat Motor nerve Skeletal muscle The heart is myogenic  Generates its own electricity

Heart beat Sinus node  Plexus of nerves  Initiates contraction of cardiac muscle Atria  Heart’s “natural pacemaker” Sinus Node (SA Node)

Heart beat AV node  Receives impulse from SA Node  Delivers impulse to the His- Purkinje System Sinus Node (SA Node) Atrio- ventricular Node (AV Node)

Heart beat Bundle of His  Begins conduction to the ventricles Sinus Node (SA Node) Atrio- ventricular Node (AV Node) Bundle of His

Heart beat Purkinje System  Bundle branches  Purkinje fibers  Moves the impulse through the ventricles for contractions Sinus Node (SA Node) Atrio- ventricular Node (AV Node) Bundle of His Bundle Branches Purkinje Fibers

Heart beat SA node AV node both atria contract 0.1 second delay Both ventricles contract

Heart beat Pacemaker is controlled by the medulla oblongata Sympathetic nerves can speed heart rate up  Noradrenaline (neurotransmitter) Increases rate of cardiac muscle contraction Parasympathetic nerves can slow heart rate down  Acetylcholine (neurotransmitter) Decreases rate of cardiac muscle contraction Adrenaline (hormone) may also increase heart beat

Heart sounds (lub-dub) 0.1 sec delay results in 2 sounds Results from closing of valves  “lub” Recoil of blood against closed AV valves  “dub” Recoil of blood against semilunar valves Heart murmur  defect in valves causes hissing sound when stream of blood squirts backward through valve

Cardiac cycle 1 complete cycle of pumping  Heart contracts & pumps  Heart relaxes & fills  Contraction phase Systole Ventricles pump blood out  Relaxation phase Diastole Atria/ventricles fill with blood systolic ________ diastolic pump (peak pressure) _________________ fill (minimum pressure) 110 ____ 70

Measuring of blood pressure High Blood Pressure (hypertension)  if top number ( systolic pumping) > 150  if bottom number ( diastolic filling) > 90

Electrocardiogram (ECG or EKG) Measures electrical impulse through heart

Electrocardiogram – P wave Atrial depolarization  Caused by impulse from SA Node

Electrocardiogram – PQ segment Delay at AV Node

Electrocardiogram – PQ segment Conduction of impulse through Bundle Branches

Electrocardiogram – PQ segment Conduction of impulse through Purkinje Fibers

Electrocardiogram – QRS wave Ventricular depolarization  Ensures synchronized contraction of ventricles Contraction begins at apex

Electrocardiogram – ST segment Interval between ventricle depolarization and repolarization

Electrocardiogram – T wave Ventricle repolarization

Normal EKG activity

Putting it all together …

Any questions?