Biology F211- Lungs

The Lungs

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Why organisms need special exchange surfaces

All living cells need certain substances to keep them alive these include:

  • oxygen for aerobic respiration
  • glucose as a source of energy
  • proteins for growth and repair
  • fats to make membranes and to be stored as energy
  • minerals to maintain their water potential and to help enzyme action

Organisms absorb these substances  from their environment or make them inside their cytoplasm as Metablosim

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What exchange surfaces look like

All good exhange surfaces have certain features in common:

  • Large surface area to volume ration
  • Thin barrier to reduce diffusion distance
  • Supply of molecules on one side keep the conc. gradient high
  • removal of required  molecules on other side keep the conc. graident low

Examples of exchange surfaces:

  • Small intestine, Liver, Root hair cell and Hyphae of fungi
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The lungs as an organ of exchange

The lungs

  • The lungs are a pair of large inflateable structures lying in the chest cavity.
  • Air can pass into the lungs through the nose and along the trachea, bronchi and bhronchioles.
  • The air finally reaches the alvioli and this is where the exchage of gases takes place

Gases pass both ways O2 from the air to the alveoli ->to blood in capilaries. CO2 passes from blood to the air in the alveoli

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How the lungs are adapted for exchange

Large surface area:

  • Provides more space for molecules to pass through
  • Individual alveoli are small but there are lots so many that the surface area is large

Barrier permeable to O2 and CO2:

  • The plasma membrane that surrond the cytoplasm of the cell form the barrier to exchange.

 

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How the lungs are adapted for exchange

Thin barrier to reduce diffusion distance 

  • Alveolus wall is one cell thick
  • Cappilary wall is one cell thick
  • Both walls consist of squamous cells (flattend cells)
  • cappilaries are in close contact with alveolus wall

 

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Inhaling and Exhaling

(http://w3.shorecrest.org/~Lisa_Peck/Physics/syllabus/phases/gases/gaswp05/seans/lungs.jpg)

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Tissue in the Lung

Cartilage:

  • The cartilage plays a structural role. It supports the trachea and bronchi, holding them open. This stops them colapsing when air pressure is low during inhalation.
  • 

Smooth muscle:

  • This muscle can contract, when the muscle contracts it will constrict the airway. Constriction mean the fow of air to the alveoli is restricted

 

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Tissue in the Lung

Elastic fibers

  • When the airway constricts, it deforms the elastic fibers in the loose tissue. as the smooth muscle relaxes the elastic fibers will recoil. this helps dialte (widen) the airway
  • 

Goblet cells

  • Secret muscus to trap tiny particles from the air these particles may include bacteria and pollen. Trapping these will reduce the risk of infection
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