Intrinsic Cardiac Conduction SystemApproximately 1% of cardiac muscle cells are
autorhythmic rather than contractile
75/min
40-60/min
30/min
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
ECG Deflection Waves
(Pacemaker) Atrial repolarization
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
ECG Deflection Wave Irregularities
Enlarged QRS =
Hypertrophy of ventricles
ECG Deflection Wave Irregularities
Prolonged QT Interval =
Repolarization abnormalities increase chances of ventricular arrhythmias.
ECG Deflection Wave Irregularities
Elevated T wave :
Hyperkalemia
ECG Deflection Wave Irregularities
Flat T wave :
Hypokalemia or ischemia
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
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
ECG Deflection Waves60 seconds ÷ 0.8 seconds = resting heart rate of 75 beats/minute
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.
Frank Starling Law of the Heart
Increased blood volume = increased stretch of myocardium
=
Increased force to pump blood out.
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.
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.
• 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
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.
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
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.
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.
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.
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.
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.
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..
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.
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
Arteriosclerosis (Atherosclerosis):
All images copyright © Camera M.D. Studios. Special thanks to Gregory Curfman, M.D..
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.