1B.Breathing and exchange of gases

• Vital Capacity:

  • Maximum volume of air a person can 'breathe in' after forced expiration
  • Includes expiratory tidal volume, reserve volume, and inspiratory reserve volume (VC = TV + ERV + IRV)
  • Significance: Helps in the diagnosis of underlying lung diseases
• Volume of air remaining in lungs after a normal expiration is called functional residual capacity (FRC) (FRC = ERV + RV)
• Diffusion of oxygen occurs in the alveolar region only:

  • Alveoli are made up of single cell layered epithelium with blood capillaries for diffusion
  • Trachea, bronchi, and bronchioles have multilayered walls without capillary network, so diffusion does not occur in these air conducting parts
• Effect of pCO2 on oxygen transport:

  • Rise in pCO2 decreases the affinity of hemoglobin for oxygen
  • Fall in pCO2 increases the affinity of hemoglobin for oxygen
• Respiratory process when going up a hill:

  • As altitude increases, pO2 in the atmosphere decreases
  • Less oxygen is obtained with each breath
  • Rate of respiration increases in response to decreased oxygen content in the blood
  • Heart rate increases to supply more oxygen to the blood
• Tidal Volume:

  • Volume of air inspired or expired during normal inspiration and expiration
  • Approximate value in a healthy human is about 500ml
  • For a minute, it is about 6000ml to 8000ml; For an hour, it is about 360000ml to 480000ml
• Oxyhaemoglobin dissociation curve is obtained when percentage saturation of haemoglobin with O2 is plotted against the pO2
• At normal conditions, this curve is sigmoid and normal
• Increasing the concentration of CO2 shifts the curve towards the right side
• Decreasing the concentration of CO shifts the curve towards the left side, forming a sigmoidal pattern
• Conchae (turbinals) are three spirally twisted bones in the respiratory part of the nasal chamber
• They regulate the temperature of inhaled air
• Chloride Shift: Exchange of chloride and bicarbonate ions between RBC and plasma at the tissues is called chloride shift (Hamburger's phenomenon)
• Occupational respiratory hazards in human beings:

  • Asbestosis: Exposure to asbestos particles causes asbestosis
  • Black Lung disease: Found in coalmine workers who inhale coal dust
  • Other disorders include silicosis (mining) and siderosis (iron)
• Muscles that help in normal breathing movements:

  • External intercostal muscles
  • Phrenic muscles of diaphragm
• Diagram of oxyhaemoglobin dissociation curve:

  • The curve shifts to the right with increased CO2 and to the left with decreased CO
  • pH and temperature also affect the curve
  • The curve is sigmoidal with varying levels of oxygen saturation at different pO2 levels