The thyroid consists of two flat, oval shaped lobes joined by an isthmus. The lobes rest either side of and slightly behind the trachea, just below the larynx in humans and most mammals. The gland is enclosed in two connective tissue capsules. Click here Cuboidal epithelial cells are arranged as roughly spherical sacs.
Basement membrane surrounds each follicle.
Groups of follicles are separated by blood vessels and connective tissue. Post ganglionic sympathetic nerve fibres from the middle superior cervical ganglia supply blood vessels and controls blood flow through the gland. Controlling blood flow alters the delivery rate of TSH, iodide and other metabolites. Under the electron microscope, large pseudopodia and an extensive network of microvilli may be observed at the apical or colloid end of the follicular cells.