• RESPIRATION

• The Respiratory Tract

      The upper respiratory tract

• Nose
• Pharynx
• Larynx
• The lower respiratory tract
• Trachea
• Bronchi
• Bronchioles
• Respiratory bronchioles
• Alveolar ducts and alveoli
• Conducting zone
• Respiratory zone
• The Lung Mechanics

  Lung pressures and ventilation

• The thorax and respiratory muscles
  • thoracic cage
  • pleural space
  • respiratory muscles during inspiration
  • respiratory muscles during expiration:
• Lung pressures
  • pleural pressure (P_pl)
  • alveolar pressure (P_A)
  • transpulmonary pressure (P_TP): P_{TP =} P_A - P_pl
  • pneumothorax
• Lung volumes and capacities (Fig 20-12)
  • spirometry
  • tidal volume (V_T)
  • 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)
• Minute respiratory volume (V, minute ventilation)

V = V_T * f (respiratory rate)

• Dead space volume (V_D)
• Alveolar ventilation (V_A): V_A = (V_T - V_D) * f

Mechanical Properties of the lung

• Lung Distensibility
• Pressure-volume curve
• Compliance (C_L= D V/D P)
• Pulmonary surfactant
• Work of breathing

W = force X distance

Factors that affect the amount of work:

• lung compliance
• surface tension
• airway resistance
• Pulmonary Circulation

  Vascular pressure and blood flow

• Pulmonary circulation is a low-pressure system
  • pulmonary arterial systemic pressure
  • pulmonary arterial diastolic pressure
  • mean pulmonary arterial pressure
  • effect of the special gravity of blood on distribution of blood flow in the lung:
• 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
• Gas Uptake and Transport

      Gases diffuse through respiratory membrane

• Dalton’s law: P_B = PO₂ + PCO₂ + PN₂ + PH₂O + PHe…
  • barometric pressure
  • partial pressures
    • PO₂ = P_B X F O₂ = 760 X 0.21 = 160 mmHg
  • vapor pressure of water
  • PO₂ in alveolar gas and venous blood: 104/40 mmHg
• Factors that affect the rate of gas diffusion through the respiratory membrane
  • thickness of respiratory membrane (alveolar-capillary membrane)
  • surface area of the respiratory membrane
    • emphysema (dissolution of alveolar walls)
  • diffusion coefficient
  • pressure difference across the respiratory membrane

  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

   Transport of carbon dioxide

• Dissolved in plasma: (7-10%)
• Carbaminohemoglobin: (15-30%)
• As bicarbonate: (60-70%)
  • CO₂ + H₂O « H₂CO_3« H⁺ + HCO₃^- catalyzed carbonic anhydrase
  • H⁺ + Hb^- « HHb
  • chloride shift

Control of Breathing

• Neural mechanisms
  • Medullary respiratory centers
  • receive synaptic inputs from the cortex and pons
  • effects of pulmonary stretch receptors (proprioreceptors)
  • failure of the respiratory center
• Chemical mechanisms
  • chemoreceptors
  • 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