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The Heart
Functions of the Heart
 Generate blood pressure
 Route blood
 Heart separates pulmonary and systemic
circulations
 Ensure one-way blood flow
 Heart valves ensure one-way flow
 Regulate blood supply
 Changes in contraction rate and force match blood
delivery to changing metabolic needs
Size, Shape, Location
of the Heart
Size of a closed fist
Shape
Apex: Blunt rounded
point of cone
Base: Flat part at
opposite end of cone
Located in thoracic
cavity within
pericardium
Heart Wall
 Three layers of tissue
 Epicardium: smooth outer
surface of heart
 Myocardium: Middle layer
made of cardiac muscle cell
and responsible for heart
contractions
 Endocardium: Smooth inner
surface of heart chambers
External Anatomy
Four chambers
2 atria
2 ventricles
Major veins
Superior vena cava
Inferior vena cava
Pulmonary veins
Major arteries
Aorta
Pulmonary trunk
Heart Valves
Atrioventricular- connect
atrium and ventricle
Tricuspid
(3 valves)- right
side
Bicuspid or mitral (2 valves)
left side
Semilunar
Aortic
Pulmonary
Prevent blood from flowing
back (one-way blood flow)
Function of the Heart Valves
Blood Flow Through Heart
Systemic and Pulmonary
Circulation
Amazing Heart Facts!
 An average adult body contains about five quarts of
blood.
 All the blood vessels in the body joined end to end
would stretch 62,000 miles or two and a half times
around the earth.
 The heart circulates the body's blood supply about
1,000 times each day.
 The heart pumps the equivalent of 5,000 to 6,000
quarts of blood each day.
Conducting System of Heart
Electrical Properties
 Resting membrane potential (RMP) present
 Action potentials
 Rapid depolarization followed by rapid, partial early
repolarization. Prolonged period of slow repolarization which
is plateau phase and a rapid final repolarization phase
 Voltage-gated channels
Action Potentials in
Skeletal and Cardiac Muscle
SA Node Action Potential
Refractory Period
 Absolute: Cardiac muscle cell completely insensitive
to further stimulation
 Relative: Cell exhibits reduced sensitivity to
additional stimulation
 Long refractory period prevents tetanic contractions
Electrocardiogram
 Action potentials through
myocardium during cardiac
cycle produces electric
currents than can be
measured
 Pattern

P wave


QRS complex



Atria depolarization
Ventricle depolarization
Atria repolarization
T wave:

Ventricle repolarization
Cardiac Arrhythmias
 Tachycardia: Heart rate in excess of 100bpm
 Bradycardia: Heart rate less than 60 bpm
 Sinus arrhythmia: Heart rate varies 5% during
respiratory cycle and up to 30% during deep
respiration
 Premature atrial contractions: Occasional
shortened intervals between one contraction
and succeeding, frequently occurs in healthy
people
Alterations in Electrocardiogram
Cardiac Cycle
 Heart is two pumps that work together, right
and left half
 Repetitive contraction (systole) and relaxation
(diastole) of heart chambers
 Blood moves through circulatory system from
areas of higher to lower pressure.

Contraction of heart produces the pressure
Cardiac Cycle
Events during Cardiac Cycle
Heart Sounds
 First heart sound or “lubb”

Atrioventricular valves and surrounding fluid vibrations as
valves close at beginning of ventricular systole
 Second heart sound or “dupp”

Results from closure of aortic and pulmonary semilunar valves
at beginning of ventricular diastole, lasts longer
 Third heart sound (occasional)

Caused by turbulent blood flow into ventricles and detected
near end of first one-third of diastole
Location of Heart Valves
Mean Arterial Pressure (MAP)
 Average blood pressure in aorta
 MAP=CO x PR
 CO is amount of blood pumped by heart per minute
CO=SV x HR
 SV: Stroke volume of blood pumped during each heart beat
 HR: Heart rate or number of times heart beats per minute
 Cardiac reserve: Difference between CO at rest and maximum
CO


PR is total resistance against which blood must be pumped
Factors Affecting MAP
Regulation of the Heart
 Intrinsic regulation: Results from normal functional
characteristics, not on neural or hormonal regulation

Starling’s law of the heart
 Extrinsic regulation: Involves neural and hormonal
control

Parasympathetic stimulation


Supplied by vagus nerve, decreases heart rate, acetylcholine secreted
Sympathetic stimulation

Supplied by cardiac nerves, increases heart rate and force of contraction,
epinephrine and norepinephrine released
Heart Homeostasis
 Effect of blood pressure
 Baroreceptors monitor blood pressure
 Effect of pH, carbon dioxide, oxygen

Chemoreceptors monitor
 Effect of extracellular ion concentration
 Increase or decrease in extracellular K+ decreases heart rate
 Effect of body temperature
 Heart rate increases when body temperature increases, heart
rate decreases when body temperature decreases
Baroreceptor and Chemoreceptor
Reflexes
Baroreceptor Reflex
Chemoreceptor Reflex-pH
Effects of Aging on the Heart
 Gradual changes in heart function, minor
under resting condition, more significant
during exercise
 Hypertrophy of left ventricle
 Maximum heart rate decreases
 Increased tendency for valves to function
abnormally and arrhythmias to occur
 Increased oxygen consumption required to
pump same amount of blood