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==Introduction==

==Introduction==

Ventilation is the movement of air into and out of the [[Lungs - Anatomy & Physiology|lungs]]. Air moves from high pressure to low pressure with the rate of flow being proportional to the pressure difference. As environmental pressure is generally constant, the [[Cardiorespiratory System - Anatomy & Physiology|respiratory system]] must change it's internal pressure to maintain air flow.

Ventilation is the movement of air into and out of the [[Lungs - Anatomy & Physiology|lungs]]. Air moves from high pressure to low pressure with the rate of flow being proportional to the pressure difference. As environmental pressure is generally constant, the [[Cardiorespiratory System Overview - Anatomy & Physiology|respiratory system]] must change its internal pressure to maintain air flow. The lungs are not fixed to the thoracic wall, but follow the changing volume of the thoracic cavity thanks to the [[Pleural Cavity and Membranes - Anatomy & Physiology#Pleural Membranes|pleura]].

 

The lungs are not fixed to the thoracic wall but follow the changing volume of the thoracic cavity thanks to the [[Pleural cavity and membranes - Anatomy & Physiology#Pleural Membranes|Pleura]].

==Inspiration==

==Inspiration==

*During Inspiration, the pressure within the [[Pleural cavity and membranes - Anatomy & Physiology|Pleural Cavity]] drops to less than the pressure of the external environment.  

During Inspiration, the pressure within the [[Pleural Cavity and Membranes - Anatomy & Physiology|pleural cavity]] drops to less than the pressure of the external environment. This is achieved by increasing the [[Lungs - Anatomy & Physiology|lung]] volume, brought about by the inspiratory muscles. The [[Diaphragm - Anatomy & Physiology|diaphragm]] contracts, causing the dome to flatten and move caudally. The [[Ribs and Sternum - Anatomy & Physiology#Thoracic Musculature|external intercostal muscles]] contract, causing the [[Ribs and Sternum - Anatomy & Physiology|ribs]] to be pulled outwards cranially.

*This is achieved by increasing the [[Lungs - Anatomy & Physiology|lung]] volume, brought about by the Inspiratory Muscles:

**[[Diaphragm - Anatomy & Physiology|Diaphragm]] - contracts - causing the dome to flatten and move caudally.

**[[Ribs and Sternum - Anatomy & Physiology#Thoracic Musculature|Intercostal muscles]] - External Intercostal Muscles contract - causing the [[Ribs and Sternum - Anatomy & Physiology|ribs]] to be pulled outwards cranially.

==Expiration==

==Expiration==

During Expiration, the pressure within the [[Pleural cavity and membranes - Anatomy & Physiology|Pleural Cavity]] increases to greater than that of the external environment, in order to expel air from the [[Lungs - Anatomy & Physiology|lungs]]. This is achieved by decreasing the lung volume, and is brought about by relaxation of Inspiratory Muscles:

 

**Dome of the [[Diaphragm - Anatomy & Physiology|Diaphragm]] is pushed back by the intrathoracic pressure.

During expiration, the pressure within the [[Pleural Cavity and Membranes - Anatomy & Physiology|pleural cavity]] increases to greater than that of the external environment, in order to expel air from the [[Lungs - Anatomy & Physiology|lungs]]. This is achieved by decreasing the lung volume, and is brought about by relaxation of inspiratory muscles. The dome of the [[Diaphragm - Anatomy & Physiology|diaphragm]] is pushed back by the intrathoracic pressure and the [[Ribs and Sternum - Anatomy & Physiology|ribs]] recoil back to their original position.

**[[Ribs and Sternum - Anatomy & Physiology|Ribs]] recoil back to their original position.

==Species Differences==

==Species Differences==

*[[Avian Respiration - Anatomy & Physiology|Avian Ventilation]] is different to mammalian ventilation, requiring different muscles.

[[Avian Respiration - Anatomy & Physiology|'''Avian''' ventilation]] is different to mammalian ventilation, requiring different muscles.

==Links==

==References==

*{{citation|initiallast = Budras|initialfirst = K.D|2last = McCarthy|2first = P.H|3last = Fricke|3first = W|finallast = Richter|finalfirst = R|year = 2002|title = Anatomy of the Dog|ed =4th|city = Hannover|pub = Schlutersche GmbH & Co. KG, Verlag und Druckerei}}

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[[Category:Respiratory System - Anatomy & Physiology]]