Download Heart Physiology Cardiac Conduction System Electrical System

Heart Physiology
Cardiac Conduction System
· ability of cardiac muscle to depolarize and contract
is intrinsic
Heart Physiology
does NOT depend on nervous system
composed of autorhythmic cells
1. pacemaker potential
2
3
1
2. depolarization
no stable resting potential
instead, Na+ channels are
opened after hyperpolarization
allowing potential to drift
toward threshold
threshold potential = -40mV
Ca2+ channels open and Ca2+ rushes into cells
3. repolarization
K+ channels open and K+ rushes out of cell
Changing the Rhythm
Electrical System
· cardiac center located in the medulla oblongata
1. Sinoatrial (SA) node
pacemaker
determines heart rate
70-80 per minute
1
2. Atrioventricular (AV) node
4
impulse pauses about 0.1 sec to
allow atria to finish contracting
3
3. Atrioventricular bundle
5
electrical connection between
atria and ventricles
4. R and L bundle branches
5. Purkinje fibers
2
sympathetic nervous system speeds up heart rate
and force (cardioacceleratory center)
parasympathetic nervous system slow down heart
rate and force (cardioinhibitory center)
· factors that affect heart rate
anxiety/stress and activity speed
up rate
meditation, yoga, sleep slow down
rate
4
highly branched
responsible for ventricular contraction
In a healthy heart, it takes 0.22 sec from SA node
stimulation to end of ventricular depolarization!
Electrocardiogram (ECG)
· aka electrokardiogram (EKG)
· recording of the electrical changes in the myocardium
· P wave - atrial depolarization
Arrhythmias
tachycardia
quickly followed by atrial contraction
· QRS complex - ventricular depolarization
quickly followed by ventricular contraction
atrial repolarization obscured by QRS complex
fibrillation
· T wave - ventricular repolarization
bradycardia
Heart Physiology
Heart Sounds
· associated with closing valves
· lub-dub, pause, lub-dub, pause, and so on
lub - AV valves (tricuspid and bicuspid) close
dub - SL valves (pulmonary and aortic) close
pause - heart resting between beats
Cardiac Cycle
· aka "heartbeat"
· mechanical actions of the heart
· each heartbeat (cycle) blood is forced out of
ventricles
· average adult pumps about 5 L/min
· stroke volume - volume of blood pumped by each
ventricle per heartbeat
· cardiac output - volume of blood pumped per
minute by the heart (both ventricles)
multiple stroke volume (mm) by heart rate (beats/min)
Cardiac Cycle (cont.)
· systole - contraction of heart muscle
· diastole - relaxation of heart muscle
· steps
1. atria contract forcing blood into relaxed ventricles
(AV valves open, SL valves closed)
2. ventricles contract forcing blood into pulmonary
trunk and aorta (AV valves closed; SL valves open)
3. both atria and ventricles relax and atria begin to fill
passively with blood (all valves closed)
Cardiac Cycle