Heart Physiology

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Heart Physiology

• The Cardiovascular System
• Topic 3
• Topic 4

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Pulmonary Circulation Systemic Circulation
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Coronary Circulation

• Heart muscle requires constant blood supply
• Right and left coronary arteries
• arise from base of aorta
• Provide oxygenated blood to myocardium
• Myocardium composed of
• Cardiac Muscle Tissue
• 20 more mitochondria than skeletal muscle!

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• Cardiac vein
• Collect deoxygenated blood from myocardium
• Drains directly into right atrium!

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Coronary Disease

• ANGINA PECTORIS
• Blockage of coronary arteries OR
• Spasm of coronary arteries
• Deficient blood supply to myocardium
• CHEST PAIN
• Treatment Vasodilators
• Most common sign of heart disease in Females

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• MYOCARDIAL INFARCTION (MI)
• Prolonged blockage of coronary arteries
• Results in death of cardiac muscle cells
• Scar tissue development
• Most dangerous in left ventricular area
• heart attack
• More common sign of heart disease in
• Males

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Risk Factors

• Genetics
• Age
• Gender
• Diet
• Inactive Lifestyle
• Smoking

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Artherosclerosis

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Heart Muscle Contraction

• Neurologically monitored/influenced by the
• AUTONOMIC NERVOUS
• SYSTEM!!
• Medulla Oblongata
• Cranial Nerve X
• Spinal Nerves

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Parasympathetic
Sympathetic
Modifying the Basic Rhythm
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Autorhythmicity

• Automatic Rhythm
• Specific areas of heart capable of
  self-depolarization!
• Depolarization ? Action Potential ? Contraction
  of Cardiac Muscle!
• Specific Areas compose the
• INTRINSIC CARDIAC CONDUCTION SYSTEM

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• Specific areas set the pace for rhythmic
  contraction of the heart!
• Specific areas ensure contraction is
• ALL OR NONE !
• Autorhythmic specific areas compose
• 1 of heart!

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So what / where are thesespecific areas

• AUTORHYTHMIC CARDIAC CELLS Found in
• Sinoatrial Node (SA Node)
• Atrioventricular Node (AV Node)
• Atrioventricular (AV) Bundle (Bundle of His)
• Bundle Branches
• Purkinje Fibers

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So How does it work?

• SA NODE starts it all!
• Generates 75 Action Potentials / minute!
• Sets the pace of hearts rhythmic contractions!
• Aka the PACEMAKER of the Heart!
• Sets pace for 40 60 heartbeats per minute
• (bpm)

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Pass the Depolarization Game

• SA Node 75 AP / minute
• AV Node 50 AP / minute
• AV Bundle 30 AP / minute
• Bundle Branches 30 AP / minute
• Purkinje Fibers stimulate myocardium
  contraction !

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Other Pacemakers?(other than the SA Node)

• Ectopic Pacemakers
• Cells outside ICCS that become over-stimulated
  and produce more APs than SA node!
• Most common cause
• Drugs
• Caffeine
• Nicotine

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• Surgical Implant
• Device inserted into chest regulates ICCS
• Functions in place of defective SA Node!

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Measuring Electrical Activity

• Electrocardiogram (EKG, ECG)
• Visual depiction of depolarization sequence among
  Nodes, bundles, branches, fibers of ICCS.
• SA Node
• AV Node
• AV Bundle
• Bundle Branches
• Purkinje Fibers

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Electrocardiogram
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NORMAL ECG

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• P Wave
• SA Node Depolarization through Atria ? Atrial
  Contraction!
• QRS Wave
• Depolarization through ventricles ? Ventricular
  contraction!
• T Wave
• Repolarization in ventricles? Ventricular Rest
  Period

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Normal sinus rhythm
No P wave SA node not functioning AV node
pacemaker
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Extra P waves Heart block
V-fib chaotic ECG no pattern
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The Cardiac Cycle
Systole--contraction--depolarization
Diastole--relaxation--repolarization
One complete heartbeat
Atrial systole
Atrial diastole
Ventricular systole
Ventricular diastole
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Start with heart totally relaxed
Period of ventricular filling
Pressure in heart is low, AV valves open,
semilunar valves closed
Blood flowing into atria pass to ventricles--70
Atrial systole forces remaining 30 into
ventricles
Atrial diastole--persists for remainder of
cardiac cycle
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Ventricular Systole
Atrial relaxation occurs as ventricles begin to
contract
? ventricular pressure closes AV valves
As ventricular pressure exceeds pressure in
attached arteries semilunar valves open
Blood forced into arteries
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Isovolumetric relaxation
ventricles relax
all valves closed briefly
ventricular pressure drops
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At 75 bpm total cardiac cycle lasts 0.8 seconds
0.1 seconds--atrial systole
0.3 seconds--ventricular systole
0.4 seconds--diastole
Blood flows along pressure gradient
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Heart Sounds
Lub-dup
Valves in heart closing
Lub--AV valves closing
Dup--semilunar valves closing
Murmurs--valvular insufficiency
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Tachycardia--increased heart rate gt100 bpm
Bradycardia--slow heart lt60 bpm
Congestive Heart Failure (CHF)
Weakened myocardium Decrease in pumping
efficiency Circulation not maintained
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