Lungs & Gas Exchange

• • When we breathe in air first passes through our mouth or nose
  • Then down the Trachea
  • Then it divides between our two bronchi
  • Then it further divides between excessive branch-like structures called bronchioles
  • Then it reaches small sacks called alveoli which are the site of gas exchange
• A single alveoli is called an alveolus.
• Alveoli are one layer of very thin cells, just like the blood capillaries they are next to. This creates a really short diffusion pathway which increases the rate at which carbon dioxide and oxygen can diffuse across.
• Alveoli have a very large surface area, if an adults alveoli were all spread out flat they would cover half a tennis court.
• The alveoli walls are moist, which allows gases to dissolve, (increases the rate of diffusion).
• The haemoglobin in the red blood cells will have already given up lots of oxygen, whereas the alveoli are full of fresh oxygen. This creates the perfect concentration gradient so the oxygen in the alveoli can diffuse into the blood easily. The oxygenated blood can now start the cycle all over again.
• The carbon dioxide in the blood will be at a higher concentration than the alveoli so it can easily diffuse across, and now we can breathe it out.
• Carbon dioxide is NOT carried by red blood cells, it is just diffused in the blood plasma.
• To calculate breathing rate use the equation:

  Number of breaths taken / number of minutes
• How are alveoli adapted for efficient gas exchange?

  Their walls are only one cell thick which provides a short distance for diffusion. There are many of them giving a large total surface area 

  They are moist, which allows the gases to dissolve, and therefore diffuse more easily.
• Lungs are in the thorax
• The thorax is the top part pf your body and is separated from the lower part by the diaphragm.
• The lungs are like big pink sponges and are protected by the ribcage. They're surrounded by pleural membranes.