Download Systemic and Pulmonary Circulation

Cardiovascular
System 2
Circuits of the Blood
There are 3 circuits:
1. Systemic Circulation
• From the left ventricle to the aorta and on to the body
• Back to the heart via the superior and inferior vena cava to the
right atrium
2. Pulmonary Circulation
• From right ventricle to the pulmonary trunk, on to the pulmonary
(left and right) arteries and to the lungs
• Back to the heart via the (left and right) pulmonary veins
3. Cardiac/Coronary Circulation
• Supply needs of the heart itself
• Arteries go to the heart branching off of the aorta
• Valveless veins return to directly to the right atrium
Systemic and Pulmonary
Circulation
20-3
Heart Skeleton
• Consists of plate of fibrous
connective tissue
between atria and
ventricles
• Fibrous rings around
valves to support
• Serves as electrical
insulation between atria
and ventricles
• Provides site for muscle
attachment
20-5
Conducting System of Heart
20-6
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
20-7
Action Potentials in
Skeletal and Cardiac Muscle
20-8
SA Node Action Potential
20-9
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
20-10
Electrocardiogram
• Action potentials through
myocardium during
cardiac cycle produces
electric currents than can
be measured
• Pattern
• P wave
• Atria depolarization
• QRS complex
• Ventricle depolarization
• Atria repolarization
• T wave:
• Ventricle repolarization
20-11
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
20-12
Alterations in
Electrocardiogram
20-13
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
20-14
Cardiac Cycle
20-15
Events during Cardiac Cycle
20-16
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
20-17
Location of Heart Valves
20-18
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
20-19
Factors Affecting MAP
20-20
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
20-21
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
20-22
Baroreceptor and Chemoreceptor
Reflexes
20-23
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
20-24