Anatomy of the thyroid gland. Development – thyroid embryogenesis

In humans, the thyroid gland is an unpaired organ in the form of a dark red or brownish-red tubercle, located on the neck in front of the upper part of the respiratory throat under the larynx. The gland consists of two lobes (right and left), interconnected by an isthmus. Sometimes the isthmus is absent, and then both lobes are in contact or separated by a gap. For many people, another lobe, which is called pyramidal, moves up from this isthmus in the form of a long outgrowth. The thyroid gland is very rich in blood vessels. Blood is delivered by four arteries, and carried away by the corresponding veins. The gland is abundantly supplied with lymphatic vessels flowing into the deep cervical lymph nodes. The thyroid gland receives innervation from the cervical sympathetic, as well as from the superior laryngeal nerve (nervus laringeus superior). Often in humans and mammals, there are additional thyroid glands in the form of small round, oval or irregularly shaped bodies that are found throughout all the organs of the branchiogenic group – from the lower jaw to the aortic arch. The development of the thyroid gland. The thyroid gland is laid as a gland with external secretion in the third week of embryonic life in the form of a thickening, and then protrusion of the ventral surface of the pharyngeal intestine at a level between the first and second gill pockets. This protrusion grows in the form of a continuous massive outgrowth in the caudal direction and soon (4th week) forms at its end a densification that is divided into the right and left lobes. The body of the gland and excretory duct (ductus thyreoglossus) are formed, connecting the gland to the pharyngeal cavity. Lateral, initially massive outgrowths form separate small lobules of the gland or follicles from the glandular lobes. Subsequently, in these follicles, first in the cells, and then between the cells, drops of a viscous substance that stains with acidic dyes appear around which the epithelial walls of the follicles begin to form. By the second half of embryonic life, gaps appear in the follicles and glandular vesicles appear, lined with epithelium and surrounded by connective tissue. At this time, quetus thyreoglossus atrophies and only a small anterior section remains in the form of foramen coecum in the tongue. There are also such anomalies when the part of the excretory duct is preserved, which in the embryonic period opened in the area of ​​the root of the tongue, and sections of the thyroid gland tissue can develop along it. The weight of the gland in a newborn is 1-2 g, with age it increases. By the age of 15 years, the weight of the gland is 11 g, by the time puberty sets in, it rapidly increases and by the age of 20 it reaches 22–25 g. In this state of iron, it stays until old age.

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