The development of the human type II pneumocyte.

Portions of lung from 25 human foetuses between 12 and 26 wk of gestational age were examined for ultrastructural changes during maturation of the epithelial cells. In 10 cases type I pneumocytes and in five cases type II cells were differentiated. The changes associated with the formation of lamellar inclusion bodies in type II cells are described. It is concluded that this is a synthetic process in which protein and lipid assembly are important. Changes in glycogen and participation of dense bodies are striking.