Thyroid gland capillaries. Coloured scanning electron micrograph (SEM) of a resin cast of capillaries in the thyroid gland. The capillaries, the smallest blood vessels, are coiled around individual secretory areas known as lobes (rounded structures). Larger blood vessels bring blood to and from the capillaries. This network of vessels exchanges gases, hormones and nutrients with the gland tissue through the permeable capillary lwalls. The thyroid gland, part of the endocrine system, lies at the base of the neck. The hormones it secretes into the bloodstream control metabolism and growth. The cast was made by injecting resin into the blood vessels. The surrounding tissues were then chemically digested.