* Respiratory system 

 * Before the concept, …What is the respiratory system?

*Respiratory system: Is an organ-system that conduit the movement of air into & Out  of the lungs {i.e. act of ventilation}…. 

 *Or in other way…A system that supply Oxygen to the tissue cells and also dispose of Co₂. {i.e. Cardiovascular/circulatory is provided}…

So, the major function of respiratory system is to supply the body with O₂ & dispose of Co₂…At least four processes accomplish this function..

*1- Pulmonary ventilation, (i.e. movement of air into & out of the lungs)..*[act of breathing]

*2- External respiration, {i.e. movement of O₂ from the lungs to the blood, & - of Co₂ from the blood to the lungs}.. i.e. exchange of O₂ & Co₂ between the blood and the lungs…

* 3- Transport of respiratory gases…so called: [internal respiration]..i.e. Transport of O₂ from the blood to the tissue cells and of Co₂ from tissue cells to the blood (this work is between the blood & the cells of the body)….

* And finally, 4- Regulation of ventilation [i.e. controlling of respiratory gases]