3-18 Glandular epithelia

The secretory cells of this type of endocrine glands are organized to form the wall of microscopic spheres or follicles. Their cells are usually a simple cubic epithelium awhose secretion accumulates inside the follicle.
The secretion held inside the follicles of the thyroid is called colloid and contains the precursors of thyroid hormones.
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 secretory activity of each follicle: they can be squamous, cuboidal or columnar – in this image they are mostly cuboidal. The colloid accumulated inside the follicles is highlighted in pink.
Groups of other endocrine cells can be seen between the follicles.
Small groups of another follicular endocrine gland are present in one part of the adenohypophysis (anterior pituitary).