Electron Microscopic Observations on the Thyroidal Colloid Secretion into the Follicular Lumen

Abstract

The colloid secretion into the thyroid follicular lumen of non-treated and adrenalin-injected domestic fowls was observed in electron microscope.
Mostly in the basal part of the follicular cell of thyroid, it is noticed the striking group of sacs of endoplasmic reticula which are filled with homogeneous material similar to the colloid in the follicular lumen. These sacs, increasing their size, come near the free surface of the cell. Thereafter, in some cases, the enlarged sacs are broken at the surfaces of the follicular cell and evacuate their contents into the follicular lumen; and in another cases, the several sacs with fragments of cell membrane and of cytoplasma, being teared off from the cell, fall into the follicular lumen in which the colloidal content flows out through the destruction of the sacs.
After these observations it is concluded that the secretion of the thyroidal colloid into the follicular lumen is of apocrine type.