Natural Heterogeneity of Thyroid Cells: The Basis for Understanding Thyroid Function and Nodular Goiter Growth*

Abstract

IN THE recent past, some of the mechanisms have been unraveled which produce the characteristic heterogeneity of shape and function among the newly generated follicles arising in the process of transformation of a normal thyroid into a multinodular goiter (1–5) (Fig. 1). The two basic findings which paved the way toward an understanding of the processes that create diversity in the offspring of a growing cell population of a normal organ are: 1. The follicular cells of a normal thyroid are not identical among themselves, but rather they have a highly individual metabolic outfit which is transferred from the mother cell to its progeny. 2. Daughter follicles produced from mother follicles during goitrogenesis arise from a few predestined follicular cells endowed with an inherited propensity to replicate at higher than average rates. From these two premises a simple syllogism leads to the conclusion that whenever a thyroid gland is forced to grow, i.e. to generate new follicles, the daughter follicles may differ from their ancestors in as many different ways as the cells that build up the hull of the mother follicle differ among themselves.