3-18 Glandular epithelia

The secretory cells of this type of endocrine gland form the wall of microscopic spheres called follicles. The secretory cells are usually a simple cubic epithelium and their product accumulates inside the sphere.
The thyroid is the best example of a follicular endocrine gland. The product of its secretion, present inside the follicle, is called colloid and contains the precursors of thyroid hormones and other molecules.
The figure highlights three follicles: their walls are formed by secretory cells highlighted in blue. The shape of the epithelial cells varies depending on the state of activity of the follicle: they can be squamous, cuboidal or columnar – in this image they are almost all cuboidal. The secretion (colloid) accumulated inside the follicle is highlighted in pink.
Groups of other endocrine cells can be seen between the follicles.
Small amounts of follicular endocrine glands are also present in a region of the hypophysis.