Respiratory physiology

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Respiratory physiology
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Respiration

• Ventilation Movement of air into and out of
  lungs
• External respiration Gas exchange between air in
  lungs and blood
• Transport of oxygen and carbon dioxide in the
  blood
• Internal respiration Gas exchange between the
  blood and tissues

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Respiratory System Functions

• Gas exchange Oxygen enters blood and carbon
  dioxide leaves
• Regulation of blood pH Altered by changing blood
  carbon dioxide levels
• Voice production Movement of air past vocal
  folds makes sound and speech
• Olfaction Smell occurs when airborne molecules
  drawn into nasal cavity
• Protection Against microorganisms by preventing
  entry and removing them

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Respiratory System Divisions

• Upper tract
• Nose, pharynx and associated structures
• Lower tract
• Larynx, trachea, bronchi, lungs

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Nasal Cavity and Pharynx
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Nose and Pharynx

• Pharynx
• Common opening for digestive and respiratory
  systems
• Three regions
• Nasopharynx
• Oropharynx
• Laryngopharynx

• Nose
• External nose
• Nasal cavity
• Functions
• Passageway for air
• Cleans the air
• Humidifies, warms air
• Smell
• Along with paranasal sinuses are resonating
  chambers for speech

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Larynx

• Functions
• Maintain an open passageway for air movement
• Epiglottis and vestibular folds prevent swallowed
  material from moving into larynx
• Vocal folds are primary source of sound
  production

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Vocal Folds
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Trachea

• Windpipe
• Divides to form
• Primary bronchi
• Carina Cough reflex

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Tracheobronchial Tree

• Conducting zone
• Trachea to terminal bronchioles which is ciliated
  for removal of debris
• Passageway for air movement
• Cartilage holds tube system open and smooth
  muscle controls tube diameter
• Respiratory zone
• Respiratory bronchioles to alveoli
• Site for gas exchange

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Tracheobronchial Tree
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Bronchioles and Alveoli
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Alveolus and Respiratory Membrane
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• Fig. 4. Effects of methacholine on depth of
  airway
• surface liquid. a control tissue not exposed to
  methacholine.
• b 2-min methacholine exposure. Putative
• sol and mucous gel are clearly visible. c 30-min
• exposure. Tissues were radiant etched for 20 s to
  1
• min. Scale bar 5 20 µm.
• From Am. J. Physiol. 274 (Lung Cell. Mol.
  Physiol. 18) L388L395, 1998.

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Lungs

• Two lungs Principal organs of respiration
• Right lung Three lobes
• Left lung Two lobes
• Divisions
• Lobes, bronchopulmonary segments, lobules

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Thoracic WallsMuscles of Respiration
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Thoracic Volume
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Pleura

• Pleural fluid produced by pleural membranes
• Acts as lubricant
• Helps hold parietal and visceral pleural
  membranes together

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Ventilation

• Movement of air into and out of lungs
• Air moves from area of higher pressure to area of
  lower pressure
• Pressure is inversely related to volume

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Alveolar Pressure Changes
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Changing Alveolar Volume

• Lung recoil
• Causes alveoli to collapse resulting from
• Elastic recoil and surface tension
• Surfactant Reduces tendency of lungs to collapse
• Pleural pressure
• Negative pressure can cause alveoli to expand
• Pneumothorax is an opening between pleural cavity
  and air that causes a loss of pleural pressure

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Normal Breathing Cycle
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Compliance

• Measure of the ease with which lungs and thorax
  expand
• The greater the compliance, the easier it is for
  a change in pressure to cause expansion
• A lower-than-normal compliance means the lungs
  and thorax are harder to expand
• Conditions that decrease compliance
• Pulmonary fibrosis
• Pulmonary edema
• Respiratory distress syndrome

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Pulmonary Volumes

• Tidal volume
• Volume of air inspired or expired during a normal
  inspiration or expiration
• Inspiratory reserve volume
• Amount of air inspired forcefully after
  inspiration of normal tidal volume
• Expiratory reserve volume
• Amount of air forcefully expired after expiration
  of normal tidal volume
• Residual volume
• Volume of air remaining in respiratory passages
  and lungs after the most forceful expiration

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Pulmonary Capacities

• Inspiratory capacity
• Tidal volume plus inspiratory reserve volume
• Functional residual capacity
• Expiratory reserve volume plus the residual
  volume
• Vital capacity
• Sum of inspiratory reserve volume, tidal volume,
  and expiratory reserve volume
• Total lung capacity
• Sum of inspiratory and expiratory reserve volumes
  plus the tidal volume and residual volume

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Spirometer and Lung Volumes/Capacities
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Minute and Alveolar Ventilation

• Minute ventilation Total amount of air moved
  into and out of respiratory system per minute
• Respiratory rate or frequency Number of breaths
  taken per minute
• Anatomic dead space Part of respiratory system
  where gas exchange does not take place
• Alveolar ventilation How much air per minute
  enters the parts of the respiratory system in
  which gas exchange takes place

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Physical Principles of Gas Exchange

• Partial pressure
• The pressure exerted by each type of gas in a
  mixture
• Daltons law
• Water vapor pressure
• Diffusion of gases through liquids
• Concentration of a gas in a liquid is determined
  by its partial pressure and its solubility
  coefficient
• Henrys law

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Physical Principles of Gas Exchange

• Diffusion of gases through the respiratory
  membrane
• Depends on membranes thickness, the diffusion
  coefficient of gas, surface areas of membrane,
  partial pressure of gases in alveoli and blood
• Relationship between ventilation and pulmonary
  capillary flow
• Increased ventilation or increased pulmonary
  capillary blood flow increases gas exchange
• Physiologic shunt is deoxygenated blood returning
  from lungs

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Oxygen and Carbon Dioxide Diffusion Gradients

• Oxygen
• Moves from alveoli into blood. Blood is almost
  completely saturated with oxygen when it leaves
  the capillary
• P02 in blood decreases because of mixing with
  deoxygenated blood
• Oxygen moves from tissue capillaries into the
  tissues

• Carbon dioxide
• Moves from tissues into tissue capillaries
• Moves from pulmonary capillaries into the alveoli

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Changes in Partial Pressures
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Hemoglobin and Oxygen Transport

• Oxygen is transported by hemoglobin (98.5) and
  is dissolved in plasma (1.5)
• Oxygen-hemoglobin dissociation curve shows that
  hemoglobin is almost completely saturated when
  P02 is 80 mm Hg or above. At lower partial
  pressures, the hemoglobin releases oxygen.
• A shift of the curve to the left because of an
  increase in pH, a decrease in carbon dioxide, or
  a decrease in temperature results in an increase
  in the ability of hemoglobin to hold oxygen

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Hemoglobin and Oxygen Transport

• A shift of the curve to the right because of a
  decrease in pH, an increase in carbon dioxide, or
  an increase in temperature results in a decrease
  in the ability of hemoglobin to hold oxygen
• The substance 2.3-bisphosphoglycerate increases
  the ability of hemoglobin to release oxygen
• Fetal hemoglobin has a higher affinity for oxygen
  than does maternal

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Oxygen-HemoglobinDissociation Curve at Rest
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Bohr effect
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Temperature effects
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Shifting the Curve
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Transport of Carbon Dioxide

• Carbon dioxide is transported as bicarbonate ions
  (70) in combination with blood proteins (23)
  and in solution with plasma (7)
• Hemoglobin that has released oxygen binds more
  readily to carbon dioxide than hemoglobin that
  has oxygen bound to it (Haldane effect)
• In tissue capillaries, carbon dioxide combines
  with water inside RBCs to form carbonic acid
  which dissociates to form bicarbonate ions and
  hydrogen ions

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Transport of Carbon Dioxide

• In lung capillaries, bicarbonate ions and
  hydrogen ions move into RBCs and chloride ions
  move out. Bicarbonate ions combine with hydrogen
  ions to form carbonic acid. The carbonic acid is
  converted to carbon dioxide and water. The
  carbon dioxide diffuses out of the RBCs.
• Increased plasma carbon dioxide lowers blood pH.
  The respiratory system regulates blood pH by
  regulating plasma carbon dioxide levels

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CO2 Transport and Cl- Movement
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Ventilation-perfusion coupling
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Respiratory Areas in Brainstem

• Medullary respiratory center
• Dorsal groups stimulate the diaphragm
• Ventral groups stimulate the intercostal and
  abdominal muscles
• Pontine (pneumotaxic) respiratory group
• Involved with switching between inspiration and
  expiration

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Respiratory Structures in Brainstem
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Rhythmic Ventilation

• Starting inspiration
• Medullary respiratory center neurons are
  continuously active
• Center receives stimulation from receptors and
  simulation from parts of brain concerned with
  voluntary respiratory movements and emotion
• Combined input from all sources causes action
  potentials to stimulate respiratory muscles
• Increasing inspiration
• More and more neurons are activated
• Stopping inspiration
• Neurons stimulating also responsible for stopping
  inspiration and receive input from pontine group
  and stretch receptors in lungs. Inhibitory
  neurons activated and relaxation of respiratory
  muscles results in expiration.

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Modification of Ventilation

• Chemical control
• Carbon dioxide is major regulator
• Increase or decrease in pH can stimulate chemo-
  sensitive area, causing a greater rate and depth
  of respiration
• Oxygen levels in blood affect respiration when a
  50 or greater decrease from normal levels exists

• Cerebral and limbic system
• Respiration can be voluntarily controlled and
  modified by emotions

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Modifying Respiration
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Regulation of Blood pH and Gases
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Herring-Breuer Reflex

• Limits the degree of inspiration and prevents
  overinflation of the lungs
• Infants
• Reflex plays a role in regulating basic rhythm of
  breathing and preventing overinflation of lungs
• Adults
• Reflex important only when tidal volume large as
  in exercise

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Ventilation in Exercise

• Ventilation increases abruptly
• At onset of exercise
• Movement of limbs has strong influence
• Learned component
• Ventilation increases gradually
• After immediate increase, gradual increase occurs
  (4-6 minutes)
• Anaerobic threshold is highest level of exercise
  without causing significant change in blood pH
• If exceeded, lactic acid produced by skeletal
  muscles

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Effects of Aging

• Vital capacity and maximum minute ventilation
  decrease
• Residual volume and dead space increase
• Ability to remove mucus from respiratory
  passageways decreases
• Gas exchange across respiratory membrane is
  reduced

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