Changes

==Introduction==

==Introduction==

Ventilation is the movement of air into and out of the 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 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 [[Respiratory System - Anatomy & Physiology|respiratory system]] must change it's 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]].

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

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

*This is achieved by increasing the lung volume, brought about by the Inspiratory Muscles:

*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 moe caudally.

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

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

**[[Ribs and Sternum - Anatomy & Physiology#Thoracic Musculature|Intercostal muscles]] - [[Ribs and Sternum - Anatomy & Physiology#Thoracic Musculature|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 orfer to expel air from the lungs. This is achieved by decreasing the lung volume, caused by relaxation of Inspiratory Muscles:

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

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

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

**Ribs recoil back to their original position.

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