Inspirational inhalation is breathing in, and so the diaphragm that sits down here will push out. Then we have the expiration exhalation and this is the breathing out. All this is managed by the diaphragm and the intercostal muscles. External respiration is an exchange of gases between the lungs and the blood, oxygen from the lungs into the blood, and CO2 from the blood into the lungs. Whereas internal respiration is the exchange of gases between cells and blood, O2 from the blood in the cells, and CO2 from the cells into the blood, so if you cut the reverse way around. What happens is we have a system that’s called gaseous exchange and gaseous exchange happens in the alveoli. On this model here, this is right down in these tiny, tiny cells down here, and this is where the body is removing the CO2, and taking in the O2 for the cells in the alveoli.