respiratory system

• functions:

  • exchange of gas between atmosphere and blood
  • protection from inhaled pathogens
  • phonation
  • detection of odours by olfactory receptors
• upper respiratory system:

  nostrils:

  • nostril dilation is advantageous when more air is required - during exercise
  • turbinate bones = warms and humidifies inhaled air and cools arterial blood that supplies brain
• lower respiratory system:

  • larynx = sound production - controlled passage of air causes vibration of vocal cords
  • lungs = elastic structures that can be stretched
• functional anatomy: conducting zone

  conducting zone = allows air to reach site of gas exchange

  • nostrils
  • nasal cavity
  • pharynx
  • trachea
  • bronchi
  • larger bronchioles
• functional anatomy: respiratory zone

  respiratory zone = site of gas exchange

  • respiratory bronchioles
  • alveolar duct
  • alveolar sac
  • alveoli
• respiratory cycle:

  • inspiratory phase followed by an expiratory phase
  • contraction and relaxation of diaphragm and external intercostal muscles
• inspiration:

  • contraction of diaphragm and external intercostal muscles
  • ribs move up and out
  • diaphragm moves out
• expiration:

  • relaxation of diaphragm and external intercostal muscles
  • ribs move in and down
  • diaphragm moves in
• types of breathing:

  • abdominal breathing: visible movement of abdomen - protrusion of abdomen during inspiration and recoiling during expiration
  • costal breathing: pronounced rib movements
• pleura:

  • a smooth membrane
  • allow lungs to have an almost friction free movement within thorax
• parietal pleura: lines the walls of the thoracic cavity
• visceral pleura: attached to the surface of lung tissue
• respiratory frequency:


  number of respiratory cycles each minute
• respiratory frequency:

  • increases during disease - indicator of health status
• states of breathing: eupnea

  • eupna = normal, quiet breathing, no deviation of frequency and depth
• states of breathing: Dyspnea

  dyspnea: difficult breathing, visible effort
• states of breathing: hyperpnea


  hyperpnea: increased depth and frequency
• states of breathing: polypnea


  polypnea: rapid shallow breathing (panting)
• states of breathing: trachypnea: 


  trachypnea: excessive rapidity of breathing
• states of breathing: bradypnea:

  bradypnea: abnormal slowness
• states of breathing: apnea

  apnea: cessation of breathing
• tidal volume:


  amount of air breathed in or out during respiratory cycle
• inspiratory reserve volume:


  amount of air that can still be inspired after inhaling the tidal volume
• expiratory reserve volume:


  amount of air that can still be expired after exhaling the tidal volume
• residual volume:


  amount of air remaining in lungs after most forceful expiration
• total lung capacity:

  • sum of all volumes
• vital capacity:


  sum of all volumes over and above residual volume - max amount of air that can be breathed in after most forceful expiration
• ventilation:

  • process of exchanging the gas in the airways and alveoli with gas from environment
  • tidal volume is used to ventilate alveoli and airways leading to alveoli
• dead space:


  represents the volume of ventilated air isn't involved in gas exchange
• anatomical dead space:


  anatomical dead space = volume of air that fills the conducting zone
• physiological dead space:


  physiological dead space = anatomic dead space + alveolar dead space
• why is there an alveolar dead space?

  some alveolar regions do not receive capillary perfusion
• Pressures that accomplish ventilation:

  • intrapulmonic pressure = pressure within lungs
  • intrapleural pressure = pressure outside lungs but within thoracic cavity
• pressures that accomplish ventilation:

  • during respiration the intrapulmonic pressure is lower than atmospheric pressure and opposite during expiration
• pressures that accomplish ventilation:

  positive pressure is primarily generated by the recoil tendency of the lungs
• diffusion of respiratory gases:

  • gases diffuse from area of high conc to low conc
  • co2 is low in atmospheric air compared to inside body - diffusion gradient from body to air
• gas exchange quick and efficient?

  because the distance between the blood and alveolar capillary and air inside an alveolus is less than 1 micrometre (small)
• oxygen transport in blood:

  • oxygen from alveoli diffuse into blood
  • oxygen enters red blood cells and binds to haemoglobin to form oxyhaemoglobin
  • binding is reversible - allows haemoglobin to pick up oxygen in the lungs and release it to body tissues
• Bohr effect:

  • change in pH causes change in oxygen - haemoglobin saturation
  • decrease in pH = greater release of oxygen from haemoglobin
• CO2 causes bohr effect:

  • when co2 diffuses into blood it diffuses into RBC and carbonic anhydrase converts CO2 to carbonic acid which dissociates into a hydrogen ion and a bicarbonate ion
  • when PCO2 rises, carbonic acid formation increases and H+ ions generated diffuse out of RBC into plasma so pH of plasma drops
  • when the PCO2 declines, the H+ ions diffuse into RBC from plasma and pH of plasma increases