human gas exchange

• Features common to all gas exchange surfaces:

  • Large surface area to allow faster diffusion of gases across the surface
  • Thin walls to ensure diffusion distances remain short
  • Good ventilation with air so that diffusion gradients can be maintained
  • Good blood supply to maintain a high concentration gradient so diffusion occurs faster
• Cilia and mucus play a crucial role in the human breathing system:

  • The passages down to the lungs are lined with ciliated epithelial cells
  • Cilia cells have tiny hairs that beat and push mucus up the passages towards the nose and throat where it can be removed
  • Mucus traps particles, pathogens like bacteria or viruses, and dust, preventing them from getting into the lungs and damaging the cells there
• lugs - bone structures that protect internal organs such as the lungs
• intercostal muscles- muscles between ribs which control its movement causing inhalation and exhalation
• diaphragm- sheath of connective tissue thast lays under thorax controling its volume to allow inhalation and exhalation
• trachea- connects mouth and nose to the lungs made from cartilage
• larynx - voice box when air passes through sounds can be made
• bronchi -each bronchus branches off into each lung
• bronchiole- bronchus split into smaller tubes called bronchioles which branch into smaler tubes called alveoli
• alveoli- are tiny air sacs where gas exchange takes place
• pleural cavity- space filled with fluid between two pleural membranes . reduces friction for lung to move freely
• passages down the lungs lined with ciliated epithelial cells .
• epithelial cells have tiny hairs at the end of them with beat to move mucus up to the throat and nose where they can be removed
• mucus produced by cells called goblet cells that are shaped like a cup
• mucus traps pathogens like bacteria and viruses as well as particles and dust, preventing them from entering lungs and damaging its cells
• Alveoli

  • The alveoli are highly specialised for gas exchange
  • There are many rounded alveolar sacs which give a very large surface area to volume ratio
  • Alveoli (and the capillaries around them) have thin, single layers of cells to minimise diffusion distance
  • Ventilation maintains high levels of oxygen and low levels of carbon dioxide in the alveolar air space
  • A good blood supply ensures constant supply of blood high in carbon dioxide and low in oxygen
  • A layer of moisture on the surface of the alveoli helps diffusion as gases dissolve