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The lung or Lungs, is an organ found with in animals that is the site of [[GASEOUS EXCHANGE|gaseous exchange]]&nbsp;<ref>Silverthorn D. (2010) Human Physiology an integrated approach, 5th edition, San Francisco: Pearson.</ref>.&nbsp;Every human is born with 2 lungs (a left lung and a right lung) and the lungs are found with in the chest cavity. They are encased in what is known as the thoracic cage; the ribs and the spine make up the outside of the cage and the diaphragm is found beneath the cage to act as a floor. 

=== External anatomy of the lungs:  ===

The left lung is divided into two lobes- the Superior lobe and the Inferior lobe, whereas the right lung is divided into three lobes- the Superior, Inferior and the Middle lobe. The Middle lobe is found between the Inferior and Superior lobe <ref>Silverthorn D. (2010) Human Physiology an integrated approach, 5th edition, San Francisco: Pearson.</ref>. 

=== Internal anatomy of the lungs:  ===

This anatomy is more complicated than the external anatomy. The [[Trachea|trachea]] which is found outside the lungs, connecting the lungs to the mouth to allow air flow, branches off into the primary bronchi (which is inside the lung) this branches off further into smaller bronchi, bronchioles and finally the alveoli. The [[Alveoli|alveoli]] is the exchange surface where gaseous exchange takes place and the other structures ([[Bronchioles|bronchioles]], [[Bronchi|bronchi]] and [[Trachea|trachea]]) make up the conducting system - passing air from the outside to the inside and ''vice versa'')&nbsp;<ref>Silverthorn D. (2010) Human Physiology an integrated approach, 5th edition, San Francisco: Pearson.</ref>. 

=== Ventilation of the lungs:  ===

During [[Ventilation|ventilation]] of the lungs, two antagonistic processes occur one after the other. [[Inhalation|Inhalation]] provides fresh [[Air|air]] to the lungs and the alveoli whereas [[Exhalation|exhalation]] removes stale air from the lungs. During inhalation the [[Diaphragm|diaphragm]] and&nbsp;the external intercostal [[Muscle|muscles]] contract&nbsp;increasing thoracic volume. This results in the drop of [[Pressure|pressure]] below the atmospheric pressure. The opposite process of exhalation, caused by the [[Contraction|contraction]] of the internal intercostal [[muscles|muscles]] and relaxation of the diaphragm, leads to the decrease in the volume of the [[Thorax|thorax]]&nbsp;<ref>Silverthorn, D. U. (1998) Human physiology: an integrated approach. Upper Saddle River, New Jersey: Prentice Hall.</ref><ref>Allott, A. (2007) IB Study Guide: Biology. Oxford: Oxford University Press.</ref>.<br> 

=== References  ===

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