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Cardiovascular System 2. Circuits of the Blood. There are 3 circuits: 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 Pulmonary Circulation

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circuits of the blood
Circuits of the Blood

There are 3 circuits:

  • 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
  • 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
  • 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
heart skeleton
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
electrical properties
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
refractory period
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
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
cardiac arrhythmias
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
cardiac cycle
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
heart sounds
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
mean arterial pressure map
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
regulation of the heart
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
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
effects of aging on the heart
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