Respiratory System

• Respiratory System


  • nasal passages

  • pharynx

  • larynx

  • trachea

  • Lungs (bronchi, bronchioles, alveoli)

  
  

  Related muscles

  • thoracic cavity

  • ribs

  • diaphragm

  
• Nose


  • air enters the body through the two external nostrils
  • the walls of the nostrils bear a fringe of hairs, which traps dust and foreign particles such as bacteria in the air
  • the nostrils lead into two nasal passages, which are lined with a moist mucous membrane. The mucus on the mucous membrane also traps dust and foreign particles
  • as air passes through the nasal passages, it is warmed and moistened
  • harmful chemicals are detected by small sensory cells in the mucous membrane
• Nose to Trachea

  • air in the nasal passages enters the pharynx
  • from the pharynx, air passes into the larynx and then into the trachea through an opening
• Trachea (windpipe)


  • the trachea is supported by C shaped rings of cartilage.
  • the cartilage keeps the lumen of the trachea open
  • the membrane next to the lumen is the epithelium, which consists of gland cells and ciliated cells
  • gland cells secrete mucus to trap dust particles and bacteria
  • ciliated cells have hair like structures called cilia on their surfaces, which sweep the dust trapped mucus up the trachea and towards the pharynx to be coughed out or swallowed
• Bronchi and Bronchioles


  • the trachea divides into two tubes called bronchi (singular : bronchus)
  • each bronchus carries air into the lungs
  • structure of bronchi are similar to trachea
  • each bronchus branches repeatedly, giving rise to numerous bronchioles which are very fine tubes that each end in a cluster of alveoli
• Alveoli (air sacs)



  • gas exchange between the alveoli and blood capillaries takes place through the walls of the alveoli
  • numerous alveoli are found in the lungs, providing very large surface area for increased rate of gas exchange
  • alveolar walls are one cell thick and very thin, provides short diffusion distance for gases, higher rate of diffusion
  • thin film of moisture covers inner wall of the alveolus, allowing oxygen to dissolve in it
  • walls of the alveoli are richly supplied with blood capillaries, the flow of blood maintains the concentration gradient of gases for diffusion

  
• Gas exchange in the alveoli

  • Gas exchange occurs by diffusion
  • blood entering the lungs has lower concentration of oxygen and higher concentration of carbon dioxide than atmospheric air entering the alveoli in the lungs, creating a concentration gradient
  • oxygen from the air dissolves into the thin film of moisture on the wall of the alveolus
  • the dissolved oxygen diffuses through wall of the alveolus and wall of the blood capillary into the red blood cells
  • oxygen combines with haemoglobin in the red blood cells to form oxyhaemoglobin
  • carbon dioxide diffuses from blood into alveolar air

  
• Concentration gradient in lungs

  • the oxygen and carbon dioxide concentration gradient between the alveolar air and the blood are maintained by a continuous flow of blood through the blood capillaries and continuous breathing, which causes air in the lungs to be constantly refreshed
• Oxygen transport around the body


  • in the lungs where oxygen concentration is high, oxygen combines with haemoglobin in the red blood cells to form oxyhaemoglobin
  • oxygenated blood is transported to other parts of the body
  • when blood passes though an organ or tissue where the oxygen concentration is low, oxyhaemoglobin will release its oxygen to the respiring cells