Respiratory System

• The respiratory system is responsible for the exchange of oxygen and carbon dioxide between the blood and alveoli
• Trachea


  Carries the air between the mouth and the lungs, has horseshoe shaped rings of cartilage to keep it open, lined with goblet cells that produce mucus and ciliated epithelial cells that waft the mucus up to the back of the throat
• Bronchi


  The trachea branches into the left and right bronchi, which lead into the left and right lungs
• Bronchioles


  The bronchi branch into bronchioles, which get narrower and have less cartilage until they end at the alveoli
• Alveoli


  Tiny air sacs where gas exchange occurs, the whole respiratory system structure is like an upside down tree with the trachea as the trunk, bronchi as the main branches, bronchioles as the smaller branches, and alveoli as the leaves
• Ventilation


  1. Movement of the thorax to get air into and out of the lungs, supplies oxygen to the lungs and removes carbon dioxide

  2. Inhalation: external intercostal muscles contract, diaphragm contracts and flattens, increases thoracic volume and decreases pressure so air rushes in

  3. Exhalation: external intercostal muscles relax, diaphragm domes upwards, decreases thoracic volume and increases pressure so air rushes out
• Gas exchange in alveoli

  • Oxygen from inhaled air dissolves in the moist alveolar lining and diffuses into the blood down its concentration gradient, binds to hemoglobin
  • Carbon dioxide from respiring cells diffuses from the blood into the alveoli down its concentration gradient, is then exhaled
• Alveoli


  • Provide a large surface area for gas exchange
  • Short diffusion distance due to thin alveolar and capillary walls
  • Type 2 pneumocytes secrete surfactant to reduce surface tension and prevent alveolar walls sticking together
• The thorax is the upper part of the body above the abdomen, its volume changes drive air movement in and out of the lungs