Breathing

• Breathing


  • refers to the muscular contraction and movements of the ribs which result in air moving in and out of the lungs
  • The taking in of air is called inhalation or inspiration
  • the giving out of air is called exhalation or expiration
• The thoracic (chest) cavity


  • the chest wall is supported by the ribs
  • between the ribs, there are two sets of muscles, the external and internal intercostal muscles.
  • the internal and external intercostal muscles are antagonistic
  • the thorax is separated from the abdomen by the diaphragm
  • the diaphragm a dome-shaped muscular elastic tissue
  • when the diaphragm muscles contract, the diaphragm flattens downwards
  • when the diaphragm muscles relax, the diaphragm arches upwards
  • the intercostal muscles and the diaphragm change the volume of the thoracic cavity

  
• Inspiration (Inhalation)

  • during inspiration, diaphragm muscle contracts and the diaphragm flattens (D contract)
  • external intercostal muscles contract while internal intercostal muscles relax (EI contract)
  • ribs move upwards and outwards, sternum moves up and forward
  • volume of thoracic cavity increases (R & S up and out)
  • lungs expand and air pressure inside lungs decreases as volume increases
  • atmospheric pressure is higher than pressure within lungs (A > L)
  • air moves into lungs

  
• Expiration (Exhalation)

  • When you expire, diaphragm muscle relaxes and diaphragm arches upwards (D relax)
  • internal intercostal mucles contract while external intercostal muscles relax (E relax)
  • ribs move downwards and inwards, sternum moves down to original position (R & S downward)
  • volume of thoracic cavity decreases, lungs are compressed and air pressure in lungs increases as volume decreases (V decreases)
  • pressure within lungs is higher than atmospheric pressure (L > A)
  • air is forced out of lungs to exterior environment

  
• inspired air vs expired air

  • Inspired air has more oxygen since oxygen from expired air is absorbed into the bloodstream
  • expired air has more carbon dioxide since carbon dioxide is released from the blood
  • expired air is more saturated with water as some water evaporates from the surfaces of the alveoli
  • heat escapes from blood into alveolar air, so expired air is around 37 degree Celsius
  • nitrogen levels are about the same

  
• Spirometer


  • a spirometer is an instrument used to measure the volume of air that enters and leaves the lungs during breathing