Human Anatomy (with the Basics of Dynamic and Sports Morphology) - Ivanitsky M. F. 2008

The Doctrine of the Organs of Internal Secretion
Thyroid Gland

The Thyroid Gland (see Fig. 144) is one of the largest endocrine Organs. Its weight ranges from 30 to 60 g. It consists of right and left lobes, an isthmus connecting them, and an inconstant pyramidal lobe extending upward from the isthmus toward the Hyoid bone. Posteriorly, the thyroid gland is adjacent to the Trachea, Larynx, and Esophagus, and anteriorly it is covered by the sternocleidomastoid, sternohyoid, sternothyroid, and omohyoid Muscles. The upper poles of the right and left lobes reach the middle of the thyroid Cartilage, while the isthmus is located at the level of the 2nd–4th tracheal rings.

The thyroid gland consists of follicles measuring 40–100 μm in diameter. These follicles are vesicles whose cavities are lined with a single-layered cuboidal epithelium composed of Cells known as thyrocytes.

Inside the cavities lies a colloid—a vitreous, sticky, yellowish substance. The follicles of the thyroid gland group together to form 1 mm lobules separated from each other by thin Connective Tissue septa, which serve as pathways for Blood Vessels and nerves. These septa extend from the capsule covering the exterior of the gland, dividing it into lobes and lobules.

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Fig. 144. Thyroid and Thymus glands of a newborn (anterior view):

1 — thyroid gland; 2 — brachiocephalic trunk; 3 — left lobe of the Thymus gland; 4 — Pericardium; 5 — right lobe of the thymus gland; 6 — SUPERIOR VENA CAVA; 7 — right brachiocephalic vein; 8 — right subclavian vein; 9 — right common carotid artery; 10 — trachea; 11 — right Internal jugular vein (after G. F. Ivanov)

The thyroid hormone, thyroxine, enhances Nitrogen METABOLISM in Tissues and increases the body's overall basal metabolic rate. The hormone thyrocalcitonin regulates calcium Metabolism in the Body and acts as an antagonist to the parathyroid hormone. Thyrocalcitonin influences skeletal development by accelerating bone growth and the ossification of epiphyseal cartilage. Congenital absence, underdevelopment, or hypofunction of the thyroid gland leads to delayed physical and mental growth, along with localized Skin edema (Myxedema). Hyperfunction results in Graves' disease (Basedow's disease), characterized by thyroid enlargement, exophthalmos (bulging eyes), tachycardia (rapid Heart rate), and increased Nervous system excitability.



Last update: 08/08/2026

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