Ultrastructure of the cell types of the anterior hypophysis in a lizard. IV. Thyrotrophs.

Abstract

Thyrotrophs do not abound in the anterior hypophysis of the teiid lizard, Cnemidophorus lemniscatus. Situated in the ventral and caudal regions, they are medium-sized rounded cells, with some angulation, having an eccentric, indented nucleus, coarse chromatin, a rather dense hyaloplasm and numerous free ribosomes. The rough endoplasmic reticulum is composed of vesicles, some tubules and, often, an isolated basal flat cisterna. The Golgi apparatus tends to be angular; small new secretory granules and many coated vesicles occur in this zone. Mitochondria are ovoid or elongate, with a dense matrix. Well constituted cilia, of the type 9 + 2, may be found in these cells. The secretory granules are spherical and small, relatively uniform in size, and somewhat variable in density. Less opaque granules show a fine structural granularity; this difference is probably due to a maturation process. A narrow light space, or halo, usually exists between the bounding membrane and the core. The number of thyrotrophs is considerably increased by 15 days after thyroidectomy. Possibly many new cells differentiate from apparent syncytial foci of amitotic divisions. At the same time, thyrotrophs become highly hypertrophic, exhibiting vesicular nuclei with dispersed chromatin, greatly expanded Golgi apparatus, and very elongated mitochondria, as well as an extensive degranulation.