1. Respiratory system

2. Function The function is to allow gas exchange to occur at the lungs.
The main features of the respiratory system include airways, lungs, and the respiratory muscles
The gas exchange is done with the blood, the gases exchanged are Carbon dioxide and oxygen

3. Inhalation
Under normal conditions, the diaphragm is the primary driver of inhalation.
When the diaphragm contracts, the ribcage expands and the contents of the abdomen are moved downward. This results in a suction pressure inside the lungs.
As the pressure in the chest falls, air moves into the conducting zone. Here, the air is filtered, warmed, and humidified as it flows to the lungs.

5. Exhalation
The lungs have a natural elasticity: as they recoil from the stretch of inhalation, air flows back out until the pressures in the chest is the same as outside the body
During forced exhalation, as when blowing out a candle, muscles including the abdominal muscles and internal muscles around the ribs, generate pressure, which forces air out of the lungs.

7. Lungs
When blood is carried to the lungs by the Pulmonary Artery it goes through narrowing passage.
By the time the Blood gets too where it is oxygenated in the lungs the passage is so small only one blood vessel at a time can fit through it.
It is then oxygenated and carried back to the heart via the pulmonary veins

8. Gas exchange with blood
The main function of the respiratory system is gas exchange.
Upon inhalation, gas exchange occurs at the alveoli, the tiny sacs which are the basic functional component of the lungs.

9. Gas exchange with blood
The alveolar walls are extremely thin in close proximity to the pulmonary capillaries which are composed of a single layer of cells.
The close proximity of these two cell types allows permeability to gases and, hence, gas exchange. This whole mechanism of gas exchange is carried by the simple phenomenon of pressure difference.

11. Blood
The whole job of the respiratory system is to exchange oxygen with carbon dioxide at the lungs.
This is needed because our body uses this oxygen to keep our muscles going. So a gas exchange is carried out at the muscles as well.