Transcript BIO 1414 Human Anatomy & Physiology II

Intrinsic Cardiac Conduction System
Approximately 1% of cardiac muscle cells are
autorhythmic rather than contractile
75/min
40-60/min
30/min
Intrinsic Conduction System
Function: 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
60 seconds ÷ 0.8 seconds = resting heart rate of 75 beats/minute
1st Degree Heart
Block = P-Q interval
longer than 0.2
seconds.
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
P T
Normal ECG
QRS
2nd Degree Block
3rd Degree Block
Not a QRS for
each P wave
No P waves. Rate
determined by
autorhythmic cells
in ventricles
Cardiac Cycle
• All events associated with a single heart
beat including atrial systole & diastole
followed by ventricular systole & diastole.
(V. Systole)
Systolic BP
Diastolic BP
(V. Diastole)
ECG Deflection Waves
60 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.
Factors influencing blood pressure
Blood Pressure = Blood Volume × Peripheral Resistance
• Blood volume loss due to injuries,
hemorrhages, use of diuretics, etc. =
BP
• Blood volume increases due to increased
water retention from increased ADH
production, IVs or transfusions = BP
Factors influencing blood pressure
Blood Pressure = Blood Volume × Peripheral Resistance
Cardiac Output = circulating blood volume
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.
Factors influencing blood pressure
Blood Pressure = Blood Volume × Peripheral Resistance
Peripheral Resistance affected by:
•blood viscosity (thickness)
(Polycythemia)
•diameter of vessels (vasoconstriction/vasodilation)
Vasoconstriction = diameter = resistance = BP
Vasodilation = diameter = resistance = BP
•elasticity of arterial walls
Elastic Arterial Walls =
BP
Homeostatic Blood Pressure
Regulation Mechanisms
• Medullary Reflex Centers:
– Cardioacceleratory - increases heart rate
– Cardioinhibitory - decreases heart rate
– Vasomotor - changes diameter of vessels
• Baroreceptors in aortic arch & carotid sinuses:
– sensitive to changes in blood pressure.
BP - Stimulates Cardioinhibitory center to
heart rate & Vasomotor center to diameter.
BP - Stimulates Cardioacceleratory 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
• Chemoreceptors in aortic bodies & carotid bodies:
– sensitive to changes in CO2 & O2 in blood.
in CO2 or in O2 stimulates Vasomotor
center to diameter (vasoconstrict) of vessels to
BP.
in CO2 stimulates Vasomotor center to
diameter (vasodilate) of vessels to BP.
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.
•
•
•
•
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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..
Acknowledgements
Most 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.