Gaseous Exchange in Lungs

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  • Created by: Hope
  • Created on: 16-03-14 13:51

Gas Exchange

Respiration = Chemical reaction that happens inside living cells to release energy, using oxygen, glucose in the blood.

Gas exchange= The process of swapping the gas that is needed (oxygen) for the waste gas (carbon dioxide) 

  • The exchange of gases occurs in the alveoli
  • Air entering the airsacs contains a lot of oxygen
  • The oxygen dissolves in the water lining the air sacs.
  • It diffuses into the blood capillaries, through the cells of the alveolus and capillary walls.
  • At the same time carbon dioxide diffuses out of the blood into the air sacs.

Characteristics of sucessful gas exchange:

  • Having a large surface area, Thin epithelial walls, An efficent blood supply, Good ventilation (breathing in and out)

Ventilation = The mechanical process used by humans, and some other animals, to help with gas exchange (breathing)

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The breathing system in humans

The lungs are situated in the chest or thorax protected by the ribcage.

The diaphragm is a sheet of muscular tissude below the lungs are separates the thorax from the abdomen. It is dome shaped which it is relaxed but flattens when it contracts.

The ribcage is moved by muscles between the ribs called intercostal muscles 

The combined movements of the ribcage and the diaphragm cause the volume of the thorax to first increase and then descrease. This causes pressure chanfged and results in air rushing in, then being forced out.

These ventilation movements maintain the diffusion fradients of oxygen into the alveoli and carbon dioxide out the alveoli. 

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Breathing in & Breathing out

Breathing in:

When we breathe in, the rib muscles contract to move the ribs upwards and outwards. 

The diaphragm contracts and moves downwards. The volume inside the chest increases and pressure decreases. This causes air to rush into your lungs and they inflate.

Breathing out:

When we breathe out, the rib muscles relax to lower the ribs downwards and inwards. The diaphgram relaxes and move upwards. The volume inside the chest decreases, pressure increase. This causes air to rush out of the lungs and they deflate. 

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Artificial Aids to Breathing

Negative pressure ventilators (iron lung)

These cause air to be sucked into the lungs.

  • A vaccum pump removes all the air, causing the ribcage to expand.
  • The pressure inside the lungs falls, so the air moves into the lungs
  • Then the vaccum is released and 'elastic recoil' cause the lungs to deflate, forcing the air out again

Positive pressure ventiliators

Force air into the patients lungs through a metal or plastic tube into the windpipe 

  • Forces a carefully measured amount of air into the lungs- once the lungs have been inflated the air pressure stops. The lungs deflate as the ribgs return to their normal position, increasing the pressure and forcing air out.
  • Advantages- No need to be 'trapped' inside an iron lung, can be used at home, patients have some control other their breathing
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