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Cardiovascular System

The HeartThe Heart

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Functions of the Heart

• Generating blood pressure• Routing blood

– Heart separates pulmonary and systemic circulations

• Ensuring one-way blood flow– Heart valves ensure one-way flow

• Regulating blood supply– Changes in contraction rate and force match

blood delivery to changing metabolic needs

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Size, Shape, Location of the Heart

• Size of a closed fist• Shape

– Apex: Blunt rounded point of cone

– Base: Flat part at opposite of end of cone

• Located in thoracic cavity in mediastinum

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Heart Cross Section

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Pericardium

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Heart Wall

• Three layers of tissue– Epicardium: This serous membrane of smooth

outer surface of heart– Myocardium: Middle layer composed of

cardiac muscle cell and responsibility for heart contracting

– Endocardium: Smooth inner surface of heart chambers

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Heart Wall

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External Anatomy

• Four chambers– 2 atria

– 2 ventricles

• Auricles• Major veins

– Superior vena cava

– Pulmonary veins

• Major arteries– Aorta

– Pulmonary trunk

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External Anatomy

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Coronary Circulation

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Heart Valves

• Atrioventricular– Tricuspid

– Bicuspid or mitral

• Semilunar– Aortic

– Pulmonary

• Prevent blood from flowing back

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Heart Valves

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Function of the Heart Valves

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Blood Flow Through Heart

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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 attachment

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Cardiac Muscle

• Elongated, branching cells containing 1-2 centrally located nuclei

• Contains actin and myosin myofilaments

• Intercalated disks: Specialized cell-cell contacts

• Desmosomes hold cells together and gap junctions allow action potentials

• Electrically, cardiac muscle behaves as single unit

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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

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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 released

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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

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Baroreceptor and ChemoreceptorReflexes

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Baroreceptor Reflex

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Chemoreceptor Reflex-pH

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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