20-1 Chapter 20 Cardiovascular System The Heart 20-2 Functions of the Heart Generating blood...
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Transcript of 20-1 Chapter 20 Cardiovascular System The Heart 20-2 Functions of the Heart Generating blood...
![Page 1: 20-1 Chapter 20 Cardiovascular System The Heart 20-2 Functions of the Heart Generating blood pressure Routing blood –Heart separates pulmonary and systemic.](https://reader038.fdocuments.in/reader038/viewer/2022110116/551c2f1e550346a84f8b6282/html5/thumbnails/1.jpg)
20-1
Chapter 20
Cardiovascular System
The HeartThe Heart
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20-2
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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20-3
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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20-5
Pericardium
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20-6
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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20-8
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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20-9
External Anatomy
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20-10
Coronary Circulation
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20-11
Heart Valves
• Atrioventricular– Tricuspid
– Bicuspid or mitral
• Semilunar– Aortic
– Pulmonary
• Prevent blood from flowing back
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20-12
Heart Valves
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20-13
Function of the Heart Valves
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20-14
Blood Flow Through Heart
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20-15
Systemic and PulmonaryCirculation
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20-16
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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20-17
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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20-18
Conducting System of Heart
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20-19
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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20-20
Action Potentials inSkeletal and Cardiac Muscle
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20-21
SA Node Action Potential
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20-22
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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20-23
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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20-24
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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20-25
Alterations in Electrocardiogram
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20-26
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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20-29
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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20-30
Location of Heart Valves
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20-31
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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20-33
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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20-34
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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20-38
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