The thyroid gland is situated in the neck, with each lobe on each side of the trachea. A lobe measures 2 inches in length, connected by a stub of tissue known as the isthmus. The thyroid is the biggest of all the endocrine glands, specifically found beneath the larynx. This organ’s high denmand for vascular support is satisfied by the two branches of the external carotid arteries, and the inferior thyroid branches of the subclavian arteries. Superior and middle thyroid veins provide venous drainage to the thyroid. The veins travel from the internal jugular veins to the inferior thyroid vein to arrive at the brachiocephalic veins. The structure of the thyroid gland is made up of microscopic thyroid follicles. These follicles look like spheroid sacs that do not contain anything inside. The sacs are lined with cuboidal epithelium that’s formed by follicular cells. The cells secrete two important thryoid hormones. Within the follicles, colloid (a protein-rich fluid) is found.
The thyroid hormones are created by epithelial cells that are found in between follicles. These cells are known as parafollicular cells, and they secrete calcitonin and thyrocalcitonin. Innervation to the thyroid gland comes from the postganglionic neurons from the superior and middle cervical ganglia. Additional innervation is supplied by the second to the seventh segment of the spinal cord with their preganglionic neurons.
The thyroid is the gland that produces the hormones thyroxine and triiodothyronine. Plus, it makes a little calcitonin. The two primary hormones that the thyroid secretes are managed by the pituitary gland’s adenohypophesis. The hormones’ release into the body is directed by thyroid follicles. Thyroxine and triiodothyronine regulate the metabolic rate of the body. They’re mainly concerned with regulation of the release of energy from carbohydrate sources and the increase of protein synthesis rate. They indicate the rate of maturation throughout the nervous system in fecal bodies. In a more developed body, they trigger the start of sexual maturity, and they regulate the rate of the body’s growth.
Calcitonin, on the other hand, is a polypeptide hormone that works with the parathyroid hormone to regulate blood calcium level and usage. An absence of calcitonin means that the kidneys would not be able to excrete calcium and bones would go weak. The two hormones maintain a stable blood calcium level.