Once more into the micro-world

Once more a dip into the microscopic world; this time a look at a thin slice of a thyroid gland. The mammalian thyroid gland is situated in the neck on the outer sides of the lower part of the larynx and upper part of the trachea. 
The gland consists almost entirely of rounded cysts, or follicles. Each follicle consists of a single layer of cuboidal cells surrounding a cavity filled with a viscous substance known as colloid which has been stained pink when preparing the slide.
The colloid is secreted by the the follicular cells and stored in the cavity until required. Its main active component is the hormone thyroxine which when released into the blood supply acts to increase the metabolic activity of almost all tissues and organs.