Ventilation: The Mechanics of Breathing

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Ventilation The Mechanics of Breathing

• Miss Ulrich

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Organs of the Respiratory system
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Lungs close up

• Bronchial Tree Consisting of the Passageways that
  Connect the Trachea and Alveoli

Q Where does gas exchange occur?
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Breathing

• The movement of air into and out of the lungs
  (ventilation) results from a pressure difference
  between the thoracic cavity and the atmosphere.
• This pressure difference is created by changing
  the volume of the thoracic cavity.

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Involuntary Respiration

• Involuntary Respiration.  The basic rhythm of
  breathing occurs without conscious effort. 
• The inspiratory center located in the medulla
  sets the basic rhythm by automatically initiating
  inspiration with a two second burst of nerve
  impulses to the diaphragm and the external
  intercostal muscles.  
• Contraction of the diaphragm  and the external
  intercostal muscles draws air into the lungs.

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The Expiratory Center.   The expiratory center is
located in the medulla.  This center functions
during forced expiration stimulating the internal
intercostal and abdominal muscles to contract.
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Inhalation

• During inhalation, the diaphragm contracts and
  flattens and the external intercostal muscles
  draw the ribs upward and outward. 
• This increase in thoracic volume results in a
  decrease in intrapulmonary pressure. 
• Air enters the lungs to stabilize the pressure
  difference between the external atmosphere and
  the internal compartments of the lungs. 
• Normal inhalation is an active process, requiring
  muscular work. 

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During quiet breathing, intercostals maintain the
rigidity of the chest wall. Otherwise, reduced
intra-thoracic pressure would cause the chest
wall to collapse inwards. External Intercostals
(on the outside of the ribcase) wrap around from
the back of the rib almost to the end of the bony
part of the rib in front. . They elevate the
ribs. Internal Intercostals in the inside of
the ribcase) extend from the front of the ribs,
and go around back, past the bend in the ribs .
They depress the ribs.
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Diaphragm

• In a healthy adult, the diaphragm is the dominant
  muscle of respiration at rest
• The diaphragm is a musculotendinous sheet
  separating the thorax from the abdomen. It is
  attached to the thoracic cage under the lower
  ribs.

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Expiration

• Exhalation is normally a passive process. 
• The diaphragm and external intercostal muscles
  relax decreasing the volume of the thoracic
  cavity. 
• This causes the pressure within the lungs to
  exceed the atmospheric pressure. 
• Air is expelled from the lungs.

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(No Transcript)
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Forced Exhalation

• During a forced exhalation, the internal
  intercostal muscles contract, depressing the rib
  cage. 
• The abdominal muscles contract, pushing the
  organs in the abdominal cavity against the
  diaphragm. 
• The thoracic volume decreases to a level lower
  than achieved in normal exhalation. 
• These muscles are used to counteract the effects
  of obstructive pulmonary disorders. 

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TIME TO BUILD OUR MODELS!
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ERV

• These muscles are used during a forced exhalation
  to determine the expiratory reserve volume (ERV).
  
• ERV is - the maximum volume of gas that can be
  forcefully exhaled after a normal exhalation
  (tidal volume).

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Other Terms of Breathing

• The volume of the lungs is divided into four
  functional compartments, lung volumes. 
  Combinations of two or more lung volumes are
  called a lung capacity.

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Spirograph pattern graph
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Terms

• tidal volume ( TV ) - the volume of gas inspired
  or expired during each normal (unforced)
  ventilation cycle (volume of air moved into the
  lungs in a single breath.
• inspiratory reserve volume ( IRV ) -the maximum
  amount of gas that can be forcefully inhaled
  after a normal inhalation.
• expiratory reserve volume ( ERV ) - the maximum
  volume of gas that can be forcefully exhaled
  after a normal exhalation.

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Terms

• residual volume ( RV ) - the amount of gas left
  in the lungs after a maximum (forced) exhalation.
  Necessary otherwise the lungs would collapse.
• total lung capacity ( TLC ) - the amount of gas
  in the lungs after a maximum (forced)
  inhalation.  TLC IRV TV ERV RV
• vital capacity ( VC ) -the maximum volume of gas
  that can be exhaled by voluntary effort after a
  maximum inhalation.  VC IRV TV ERV

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Terms

• inspiratory capacity ( IC ) - the maximum amount
  of gas that can be inhaled after a normal
  (unforced) exhalation.    IC IRV TV
• functional residual capacity ( FRC ) - the amount
  of gas left in the lungs after a normal
  (unforced) exhalation.  FRC   ERV RV