Reid's Rules of Development

1. The bronchial tree is developed by the sixteenth week of intrauterine life.
2. Alveoli develop after birth, increasing in number untiil the age of eight years and in size until growth of the chest wall finishes with adulthood.
3. The pre-ascinar vessels (arteries & veins) follow the development of the airways, the intra-acinar that of the alveoli. Muscularization of the intra-acinar arteries does not keep pace with the appearance of new arteries.

* Conducting airways receive blood supply from the bronchial arteries. Ascinar units receive blood supply from the pulmonary arteries.