Download Ch 11 sec 2

Heart Physiology
CH 11 Anatomy and
Physiology
Conduction of Impulses
• Cardiac muscle can contract without nerve
stimulation
• Different cells contract at different rates
– Atria 1/sec
– Ventricles 1/5sec
– Must be regulated
• Autonomic nerves control rate
• Intrinsic Conduction System (pacemaker)
Intrinsic Conduction System
• Also called the nodal system
• Composed of a hybrid muscle/nervous
tissue
• Sets the rhythm at around 75 bpm
• SA node is the pacemaker
• AV node contracts atria
• AV bundle carries signal to apex
• Purkinje fibers contract ventricles
Poor conduction
• Damage to AV node is called heart block
– Ventricles contract on their own
• Damage to SA node
– May need internal pacemaker
• Major damage due to ischemia may
disrupt normal conduction
– Ventricles may go into fibrillation
• Major cause of death in MI patients
• Can require defibrillation (AED)
Electrocardiogram (ECG)
• Electrical signals in
the heart can be
traced externally
• Electrodes are placed
on the skin
• P wave atria
depolarize
• QRS ventricles
depolarize
• T wave Vent Repolar
Cardiac Cycle
•
•
•
•
One complete heart beat
Systole is contraction
Diastole is relaxation
In cardiac cycle they apply to the
ventricles unless otherwise noted
• Average 75 bpm or 1/0.8 sec
• 1. heart relaxed and filling, AV valves open, end with
atrial contraction
• 2. AV valves close due to increased pressure,
semilunar vales forced open, atria relax and fill
• 3. ventricles relax, AV valves reopen and ventricles
refill
Heart Sounds
• AV valve closing before ventricular
contraction causes “lub” sound
– Long and loud
• Semilunar valves closing after contraction
makes “dub” sound
– Short and sharp
• Any abnormal sound is called a murmur
– May be normal or pathological
Cardiac Output (CO)
• Product of stroke volume (SV) and heart
rate (HR)
• CO = SV x HR
• CO = 70 ml/beat x 75 beats/min
= 5250 ml/min entire volume is 6000 ml
• A change in either results in a change in CO
Changing SV
• Stroke volume related to stretch on
ventricle wall
• Increase venous return increases volume
leading to more stretch
– Exercise increases heart rate and muscular
pump action
Changing HR
• ANS control
– Sympathetic increases HR in times of
demand
– Parasympathetic slows the HR when crisis is
over (Vagus Nerve)
• Drugs such as digitalis
• Hormones
• Ions
Homeostatic Imbalance of pumping
• Congestive Heart Failure (CHF)
– Progressive condition
– Caused by coronary athlerosclerosis
– Left side failure leads to lung congestion
– Right side failure leads to peripheral swelling
– Failure of one side puts stress on the other
and will lead to total failure if untreated