The early development of the pars distalis of human foetal pituitary gland.

Abstract

A histochemical and ultrastructural investigation of the early development of the adenohypophysis was carried out on a human material. Special attention was paid to an accumulation of hyaluronic acid and chondroitin-4-and/or-6-sulfate in the mesenchyma; its role in morphogenesis of the Rathke's pouch is discussed. The role of the vessels as a “critical factor” in the budding of the parenchyma and in the differentiation of secretory cells is discussed. Canalicular extensions from the original lumen of the pouch into the core of parenchymal buds, which migrate into the mesenchyma, is a new observation. The participation of canaliculi in formation of follicular structures of pars distalis is described and discussed. The primitive cell type lining the pouch is also found in the wall of canaliculi and follicular structures. The cell type is described and its role as the real progenitor cell of the adenohypophysis is discussed. Three types of colloid are noticed in pars distalis: 1. In the follicular structures, 2. in the slits or clefts caused by partial occlusion of the lumen of the pouch, and 3. mesenchymal extravasal colloid presumably representing material squeezed out from the aforementioned clefts or slits. It is concluded that the colloid contains material secreted from different types of granulated cells as well as material from the surface coat of the luminal cells.