Unit 9

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Unit 9 The Heart

• Cardiovascular System
• The 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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The Closed Circulatory System

• Humans have a closed circulatory system, typical
  of all vertebrates, in which blood is confined to
  vessels and is distinct from the interstitial
  fluid.
• The heart pumps blood into large vessels that
  branch into smaller ones leading into the organs.
• Materials are exchanged by diffusion between the
  blood and the interstitial fluid bathing the
  cells.

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The Cardiovascular System
Three Major Elements Heart, Blood Vessels,
Blood
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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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Lets Practice.
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Did you get them all correct?
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Blood Flow Through Heart
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Systemic and PulmonaryCirculation
Pulmonary circuit The blood pathway between the
right side of the heart, to the lungs, and back
to the left side of the heart. Systemic
circuit The pathway between the left and right
sides of the heart.
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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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The Circulatory System

• Blood Vessels -A network of tubes
• Arteries?arterioles move away from the heart
• Elastic Fibers
• Circular Smooth Muscle
• Capillaries where gas exchange takes place.
• One cell thick
• Serves the Respiratory System
• Veins?Venules moves towards the heart
• Skeletal Muscles contract to force blood back
  from legs
• One way values
• When they break - varicose veins form

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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
• MAPCO x PR
• CO is amount of blood pumped by heart per minute
• COSV 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
• Starlings 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