Submicroscopical aspects of chick embryo parathyroid glands

Abstract

Parathyroid glands from chick embryos ranging from 8 days of incubation up to hatching time were fixed in half-strength Karnovsky's fixative, postfixed in osmium tetroxide, stained in bulk with 2% uranyl acctate, dehydrated, and embedded in Araldite. Thick sections were stained with toluidine blue and thin ones with lead citrate. At all ages, the gland was formed by cords of cells which appeared darkly stained by the toluidine blue, and electron opaque with the electron microscope. Few clear cells were intermingled with the main cell type. The cytoplasm of dark cells contained at all ages, free ribosomes, mitochondria with a dense matrix, a well developed Golgi complex, profiles of rough-surfaced endoplasmic reticulum, coated vesicles, lipid droplets, and lysosomes. After day 13 of incubation, small vesicles containing a material of low density (prosecretory granules) appeared in the Golgi zone. The presence of these cytoplasmic elements tends to support the idea that the glands are already active during the embryonic period. The role of clear cells has not been established. Islands of apparently active ultimobranchial “C” cells were found with some frequency within the parathyroid glands.