Embryology of the lungs

Ok, I'm ignoring development of the upper airways, pleura and diaphragm here (mainly because we didn't discuss it and I'll try and deal with it later)

Endoderm forms the epithelia.
Splanchnic mesoderm and neural crest cells form the cartilage, connective tissue and muscles.

So there are roughly 5 stages:
1. Embyonic (from the 4th week)
Development begins in the 4th week where there forms a respiratory (or laryngotracheal) diverticulum (from an opening in the foregut in the embryo).
The diverticulum grows and then folds (tracheo-oesophageal folds) to create the tracheo-oesophageal septum to separate the trachea and lung buds from the oesophagus. There is still a connection with these two - via the larynx which forms from the 4th and 6th pharyngeal arches.
The lung buds are two divisions of the trachea, and these continue to divide so that by 6 months there are more than 17 subdivisions.
2. Psuedoglandular (5-17 weeks)
All of the elements of the lungs have developed except those involved in gas exchange
3. Canalicular (16-25 weeks)
Increase in vascularity of the lungs. Respiratory bronchioles and alveolar ducts form.
4. Saccular (24weeks to birth)
Increase in the number of terminal sacs.
Cuboidal cells become flat squamous epithelia.
By week 20 Type II alveolar cells have been producing surfactant.
Further development of the capillary network
5. Alveolar (late fetal - childhood)
Where alveoli form and continue to develop after birth