Editing Respiratory system (section)

===Control of ventilation===
{{Main|Control of ventilation}}
Ventilation of the lungs in mammals occurs via the [[respiratory center]]s in the [[medulla oblongata]] and the [[pons]] of the [[brainstem]].<ref name=tortora1 /> These areas form a series of [[neural pathway]]s which receive information about the [[Blood gas tension|partial pressures of oxygen and carbon dioxide]] in the [[arterial blood]].  This information determines the average rate of ventilation of the [[Pulmonary alveolus|alveoli]] of the [[lungs]], to keep these [[Homeostasis#Levels of blood gases|pressures constant]]. The respiratory center does so via [[Motor neuron|motor nerves]] which activate the [[Thoracic diaphragm|diaphragm]] and other [[muscles of respiration]].

The breathing rate increases when the [[PCO2|partial pressure of carbon dioxide]] in the blood increases. This is detected by [[Central chemoreceptors|central blood gas chemoreceptors]] on the anterior surface of the [[medulla oblongata]].<ref name=tortora1 /> The [[Aortic bodies|aortic]] and [[carotid body|carotid bodies]], are the [[Peripheral chemoreceptors|peripheral blood gas chemoreceptors]] which are particularly sensitive to the arterial [[Pulmonary gas pressures|partial pressure of O<sub>2</sub>]] though they also respond, but less strongly, to the partial pressure of [[Carbon dioxide|CO<sub>2</sub>]].<ref name=tortora1 /> At sea level, under normal circumstances, the breathing rate and depth, is determined primarily by the arterial partial pressure of carbon dioxide rather than by the arterial [[blood gas tension|partial pressure of oxygen]], which is allowed to vary within a fairly wide range before the respiratory centers in the medulla oblongata and pons respond to it to change the rate and depth of breathing.<ref name=tortora1 />

[[Physical exercise|Exercise]] increases the breathing rate due to the extra carbon dioxide produced by the enhanced metabolism of the exercising muscles.<ref name= ritchisong>{{cite web|title=Respiration|url=http://people.eku.edu/ritchisong/301notes6.htm|publisher=Harvey Project|access-date=27 July 2012}}</ref> In addition, passive movements of the limbs also reflexively produce an increase in the breathing rate.<ref name=tortora1 /><ref name= ritchisong />

Information received from [[stretch receptor]]s in the lungs' limits [[tidal volume]] (the depth of inhalation and exhalation).