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 atrium2. 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 PulmonaryCirculation

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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

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Conducting System of Heart

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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

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Action Potentials inSkeletal and Cardiac Muscle

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SA Node Action Potential

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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

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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

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Alterations in Electrocardiogram

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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

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Cardiac Cycle

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Events during Cardiac Cycle

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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

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Location of Heart Valves

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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

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Factors Affecting MAP

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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 released20-21

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 decreases20-22

Baroreceptor and ChemoreceptorReflexes

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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

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