Gaseous Exchange and Ventilation.

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Gaseous Exchange and Ventilation

  • Breathing draws fresh air into the lungs and forces stale air out. This is called ventilation. Ventilation ensures that there is always a good supply of ‘fresh air’ inside the lungs. This maintains large diffusion gradients for oxygen and carbon dioxide between air and blood. Large diffusion gradients mean efficient gas exchange.

  • Respiration and ventilation are different. Respiration occurs in a series of oxidation reactions that occur in cells

  • The organs of gaseous exchange in the mammal are lungs.

  • Lungs are housed in the thorax, a chamber formed by the rib cage and its muscles (intercostal muscles), with a domed floor, the diaphragm.

  • Lungs are connected to the pharynx at the rear of the mouth by the trachea. The trachea, supported by incomplete rings of cartilage, runs beside the oesophagus before dividing into bronchi, one to each lung
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  • Within the lung the bronchus divides into smaller bronchioles. The walls of bronchi and larger bronchioles are also supported by rings or tiny plates of cartilage, preventing collapse.

  • Breathing in is called inspiration. The volumes in the lungs increase. The intercostal muscles contract. The ribcage moves upwards and outwards. The diaphragm contracts and moves them downwards. The volume in the thorax increases. The pressure in the lungs is less than in the thorax. Therefore, the air moves into the lungs until it reaches atmospheric pressure.

  • Breathing is called expiration. The volumes in the lungs decrease. The intercostal ...

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