Exchange surfaces and breathing

Exchange surfaces and breathing

1. Gas exchange

   • Cells need to take in oxygen and excrete waste products like CO2
   • Small organisms have a large SA:V ratio. Large organisms have a small SA:V ratio.
     • Small organisms can diffuse directly into or out the surface membrane. Small distance and is quicker
     • Large organisms have cells deep within the body, large distance. Difficult to exchange substance to supple a large volume through a small surface
   • Trachea 2 bronchi bronchioles alveoli
   • Gas exchange happens in the alveoli
     • Surrounded by capillaries. O2 diffuses out of the alveoli in the blood and CO2 diffuses into the alveoli from the blood

2. Gas exchange systems

   • How the lungs are adapted
     • Many alveoli provide large surface area
     • Alveolar and capillary epithelium are one cell thick, short diffusion pathway
     • Alveoli have a good blood supply, take away O2 and bring back CO2.
     • Breathing in and out keeps a fresh supply of air and concentration gradient high
   • Role of each tissue
     • Goblet cells
       • Secrete mucus that traps microorganisms and prevents them from reaching alveoli
     • Cilia
       • Wafts the mucus to the back of the throat to prevent lung infection
     • Elastic fibres
       • They stretch and recoil to help with breathing in and out
     • Smooth muscle
       • Allows the diameter of the lumen to be controlled.
     • Cartilage
       • Provide support and stops the trachea from collapsing (in a C shape)

3. Breathing

   • Inspiration
     • Expiration
       • Intercostal and diaphragm muscles relax. Ribcage moves down and in, diaphragm becomes curved. Decreases volume of thorax and increases pressure in lungs. Air forced out
     • Intercostal and diaphragm muscles contract. Ribcage moves up and out, diaphragm flattens. Increases volume of thorax. Lung pressure decreases. Air flows into the lungs
   • Terms
     • Tidal volume: volume of air in each breath at rest
     • Vital capacity: maximum volume of air breathed in or out
     • Breathing rate: how many breaths (p/min)
     • Residual volume: air that remains in the lungs (1.5dm3)
     • Expiritory/Inspiritory reserve: How much more air can be breathed in or out
   • Spirometer
     • Oxygen filled chamber, person breaths through a tube, movements recorded (spirometer trace), soda lime absorbs CO2.
       • Volume of air decrease because CO2 in absorbed