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Intrinsic Cardiac Conduction SystemApproximately 1% of cardiac muscle cells are
autorhythmic rather than contractile
75/min
40-60/min
30/min
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Intrinsic Conduction SystemFunction: initiate & distribute impulses so heart depolarizes & contracts in orderly
manner from atria to ventricles.
SA node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
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ECG Deflection Waves
(Pacemaker) Atrial repolarization
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ECG Deflection Waves
1st Degree Heart Block = P-Q interval longer than 0.2 seconds.
60 seconds ÷ 0.8 seconds = resting heart rate of 75 beats/minute
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ECG Deflection Wave Irregularities
Enlarged QRS =
Hypertrophy of ventricles
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ECG Deflection Wave Irregularities
Prolonged QT Interval =
Repolarization abnormalities increase chances of ventricular arrhythmias.
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ECG Deflection Wave Irregularities
Elevated T wave :
Hyperkalemia
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ECG Deflection Wave Irregularities
Flat T wave :
Hypokalemia or ischemia
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Heart Blocks
Normal ECG
3rd Degree Block
No P waves. Rate determined by autorhythmic cells in ventricles
2nd Degree BlockNot a QRS for each P wave
P
QRS
T
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Cardiac Cycle• All events associated with a single heart
beat including atrial systole & diastole followed by ventricular systole & diastole.
(V. Systole) (V. Diastole)
Systolic BP
Diastolic BP
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ECG Deflection Waves60 seconds ÷ 0.8 seconds = resting heart rate of 75 beats/minute
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Frank Starling Law of the Heart
• The more cardiac muscle is stretched within physiological limits, the more forcibly it will contract.
• Rubber band analogy
• Increasing volumes of blood in ventricles increase the stretch & thus the force generated by ventricular wall contraction.
• Greater stretch means more blood volume is pumped out, up to physical limits.
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Frank Starling Law of the Heart
Increased blood volume = increased stretch of myocardium
=
Increased force to pump blood out.
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Terms, Definitions & Units• Blood Pressure - force generated against
arterial walls per unit of area in mm Hg.
• Systolic Pressure - peak arterial pressure. Averages about 120 mm Hg in healthy adults.
• Diastolic Pressure - lowest arterial pressure. Averages between 70 - 80 mm Hg in healthy adults.
• Blood Volume - quantity of blood in cardiovascular system. Varies from 4-5 L. in females to 5-6 L. in males.
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Terms, Definitions & Units
• Cardiac Output - the amount of blood pumped by a ventricle per minute. Units may be in milliliters or Liters per minute.
• Heart Rate - number of cardiac cycles per minute. Average for males = 64-72/min. Average for females = 72-80/min.
• Stroke Volume - amount of blood pumped out of a ventricle each beat. Average resting stroke volume = 70 ml.
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• Blood volume increases due to increased water retention from increased ADH production, IVs or transfusions = BP
• Blood volume loss due to injuries, hemorrhages, use of diuretics, etc. = BP
Blood Pressure = Blood Volume × Peripheral Resistance
Factors influencing blood pressure
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Cardiac Output = circulating blood volume
Blood Pressure = Blood Volume × Peripheral Resistance
Factors influencing blood pressure
Cardiac Output = Heart Rate × Stroke Volume
Increased heart rate caused by the release of epinephrine into blood by the adrenal glands = increased cardiac output, which increases circulating blood volume, to increase blood pressure.
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Vasodilation = diameter = resistance = BP
Peripheral Resistance affected by:
•blood viscosity (thickness)
•diameter of vessels (vasoconstriction/vasodilation)
Blood Pressure = Blood Volume × Peripheral Resistance
Factors influencing blood pressure
Vasoconstriction = diameter = resistance = BP
Elastic Arterial Walls = BP
(Polycythemia)
•elasticity of arterial walls
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BP - Stimulates Cardioinhibitory center to heart rate & Vasomotor center to diameter.
Homeostatic Blood Pressure Regulation Mechanisms
• Medullary Reflex Centers:
– Cardioacceleratory - increases heart rate
– Cardioinhibitory - decreases heart rate
– Vasomotor - changes diameter of vessels
BP - Stimulates Cardioacceleratory center to heart rate & Vasomotor center to diameter.
• Baroreceptors in aortic arch & carotid sinuses:
– sensitive to changes in blood pressure.
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in CO2 or in O2 stimulates Vasomotor center to diameter (vasoconstrict) of vessels to BP.
Homeostatic Blood Pressure Regulation Mechanisms
• Medullary Reflex Centers:
– Cardioacceleratory - increases heart rate
– Cardioinhibitory - decreases heart rate
– Vasomotor - changes diameter of vessels
in CO2 stimulates Vasomotor center to diameter (vasodilate) of vessels to BP.
• Chemoreceptors in aortic bodies & carotid bodies:
– sensitive to changes in CO2 & O2 in blood.
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Aneurysm• Weakness of the wall of an artery causing
an abnormal enlargment or bulge.
• The aorta or the arteries that supply the heart, brain, legs or kindeys are most commonly affected.
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Angina Pectoris
• Medical term for chest pain due to coronary heart disease.
• It occurs when the myocardium doesn’t get as much blood (Oxygen) as it needs.
• Insufficient blood supply is called ischemia.
• May initially occur during physical exercise, stress, or extreme temperatures.
• It is a sign of increased risk of heart attack.
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Hypertension
• High blood pressure.• Sustained arterial blood pressure of 140/90
mm Hg or above.• Rising diastolic pressure generally indicative
of progressive hardening of arteries.• Since the heart must work harder to pump
blood against higher pressures, there is increased risk of a cardiovascular accident.
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Hypotension
• Abnormally low blood pressure.
• Sustained systolic blood pressure of below 100 mm Hg.
• Generally associated with lower risk of cardiovascular accidents & long life providing that the tissues are adequately perfused..
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Circulatory Shock• Blood vessels inadequately filled to enable
normal circulation & supply of O2 & nutrients.
• May result in death of cells & damage to organs.
• Common Types:
• Hypovolemic - severe blood loss
• Cardiogenic - heart (pump) failure
• Vascular - excessive vasodilation
• Septicemic - vasodilation due to bacterial toxins produced during an infection.
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Atherosclerosis (Arteriosclerosis)
• Narrowing and hardening of arteries and impairment of blood flow due to the deposition of fatty materials and calcium in their walls.
• Risk factors include:– smoking– inactivity– diabetes– high blood cholesterol– personal or family history of heart disease
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Arteriosclerosis (Atherosclerosis):
All images copyright © Camera M.D. Studios. Special thanks to Gregory Curfman, M.D..
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AcknowledgementsMost of the figures used in this presentation came from the Benjamin Cummings Digital Library
Version 2.0 for Human Anatomy & Physiology, Fifth Edition. Other figures came from public domain internet sources and software in the possession of the author.