1' The Respiratory Tract

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RESPIRATION

• 1. The Respiratory Tract
• A. The upper respiratory tract
• Nose
• lined by ciliated columnar epithelium
• mucus secreting cells
• dense vascular network in submucosa
• filtering air
• warming air
• humidifying air
• sneezing reflex

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• Pharynx
• Epiglottis
• Larynx
• vocal cords
• glottis
• B. The lower respiratory tract
• Trachea
• Bronchi
• Bronchioles
• Respiratory bronchioles
• Alveolar ducts and alveoli

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• Conducting zone
• to warm and humidify the air
• to distribute the gas
• to serve as part of body defense system
• Respiratory zone

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• Respiratory tract defense system
• Mucocilliary transport system mucus escalator
• Cough reflex
• Macrophages

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• 2. The Lung Mechanics
• A. Lung pressures and ventilation
• The thorax and respiratory muscles
• thoracic cage ribs (12), sternum, diaphragm
• pleural space
• respiratory muscles during inspiration
• diaphragm
• external intercostal muscles
• accessory muscles
• respiratory muscles during expiration
• Diaphragm
• internal intercostal muscles
• abdominal walls

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• Lung pressures
• Air flows because of pressure gradients
• pleural pressure (Ppl)
• alveolar pressure (PA)
• Pressure changes during respiratory cycle
• pneumothorax

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• Lung volumes and capacities
• Spirometry
• tidal volume (VT)
• inspiratory reserve volume (IRV)
• expiratory reserve volume (ERV)
• residual volume (RV)
• inspiratory capacity (IC)
• functional residual capacity (FRC)
• vital capacity (VC)
• total lung capacity (TLC)
• forced vital capacity (FVC)

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• FEV1 timed forced expiratory volume in one
  second
• FEV1/FVC 80 more useful for detecting
  obstructive vs restrictive lung diseases

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• Minute respiratory volume (V, minute ventilation)
• V VT f (respiratory rate)
• Dead space volume (VD)
• Alveolar ventilation (VA) VA (VT - VD) f

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• B. Mechanical Properties of the lung
• Lung Distensibility
• Pressure-volume curve
• Compliance (CL DV/DP)
• Pulmonary surfactant
• surface tension
• Laplace Law P 2T/r
• atelectasis

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• Work of breathing
• W force X distance
• Factors that affect the amount of work
• lung compliance
• surface tension
• airway resistance
• R ? L ? /r4
• diameter of the airways
• Bronchoconstriction histamine
• Broncodilation CO2, EP (?2 receptors)

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• 3. Pulmonary Circulation
• A. Vascular pressure and blood flow
• Pulmonary circulation is a low-pressure system
• pulmonary arterial systemic pressure 25 mmHg
• pulmonary arterial diastolic pressure 10 mmHg
• mean pulmonary arterial pressure 15 mmHg
• effect of the special gravity of blood on
  distribution of blood flow in the lung
• poor perfusion in the upper lung (functional dead
  space volume)

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• Hypoxic vasoconstriction balances blood flow with
  ventilation
• regional hypoxia/hypoxemia
• hypoxic vasoconstriction - a mechanism that
  balances the perfusion of blood with the
  availability of regional ventilation
• effect of hypoxic vasoconstriction at the high
  altitude
• Exercise recruits capillaries and decreases
  transit time

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• 4. Gas Uptake and Transport
• A. Gases diffuse through respiratory membrane
• Daltons law PB PO2 PCO2 PN2 PH2O PHe
• barometric pressure PB at the sea level 760
  mmHg
• partial pressures
• PO2 PB X F O2 760 X 0.21 160 mmHg
• vapor pressure of water
• PO2 in alveolar gas and venous blood 100/40 mmHg

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Gas exchangealveoli and cells
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• Factors that affect the rate of gas diffusion
  through the respiratory membrane
• thickness of respiratory membrane
  (alveolar-capillary membrane) normally 0.1 - 0.5
  µm
• pulmonary edema
• fibrosis of the lung
• surface area of the respiratory membrane 70 m2
  in the normal adult
• emphysema (dissolution of alveolar walls)
• diffusion coefficient
• solubility in water
• molecular weight
• carbon dioxide diffuses 20 times as rapidly as
  oxygen
• pressure difference across the respiratory
  membrane

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Respiratory membrane
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• Pulmonary pathologies

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• B. Transport of oxygen
• Transport of oxygen in the dissolved state
• only 2 of oxygen transported in the dissolved
  state in the water of the plasma and cells
• Transport of oxygen by hemoglobin
• 98 oxygen is carried to the tissues by
  reversible combination with hemoglobin
• oxygen carrying capacity 20 ml/100ml blood
• oxygen saturation percent O2 saturation O2
  content/O2 capacity x 100
• oxyhemoglobin dissociation curve
• factors that affect the oxyhemoglobin curve

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Oxygen-hemoglobin dissociation
"2,3-DPG and oxygen/Hb binding"

• Factors that affect the oxyhemoglobin curve

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• Factors contributing to the total oxygen content
  of arterial blood

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• D. Control of Breathing
• Neural mechanisms
• Medullary respiratory centers
• inspiratory neurons set the rhythm
• expiratory neurons
• receive synaptic inputs from the cortex and pons
• effects of pulmonary stretch receptors
  (proprioreceptors)
• failure of the respiratory center
• by physical damages (concussions, cerebral edema)
• by overdose of chemical substances (barbiturate,
  anesthetics)

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• Reflex control of ventilation
• Chemoreceptors monitor blood gases and pH
• Control centers in the brain stem regulate
  activity to respiratory muscles

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• Chemical mechanisms
• chemoreceptors
• central chemoreceptors (in the medulla) monitor
  only H in CSF
• peripheral chemoreceptors (aortic bodies and
  carotid bodies)
• control of the alveolar ventilation by the
  arterial CO2
• control of the alveolar ventilation by the
  arterial H exclusively by peripheral
  chemoreceptors
• control of the alveolar ventilation by the
  hypoxia relatively insensitive to hypoxia

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Central chemoreceptor
Carotid body oxygen sensor
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Chemoreceptor reflex