Thyroid. Structure, functions

The thyroid glandula, thyroid glandula, is unpaired, the largest of the endocrine glands. It is located in the anterior part of the neck, side and front of the larynx and trachea , as if embracing them. The gland has the shape of a horseshoe with a concavity facing posteriorly and consists of two unequal lateral lobes: the right lobe, the lobus dexter, and the left lobe, the lobus sinister, and connecting the two lobes of the unpaired thyroid isthmus glandulae thyroideae. The isthmus can be absent, and then both lobes loosely adjoin one another.

Thyroid. Structure, functions.

Sometimes there are additional thyroid glands, glandulae thyroideae accessoriae, similar in structure to the thyroid gland, but either not associated with it, or connected to it by a small thin strand.

Often (in a third or half of cases) from the isthmus or from the left lobe, at the border with the isthmus, the pyramidal lobe, lobus pyramidalis, which can reach the upper thyroid lobe or the body of the hyoid bone, is directed upward .

The thyroid gland is covered from the outside with a fibrous capsule, capsula fibrosa. The capsule is a thin fibrous plate, which, growing together with the parenchyma of the gland, sends the processes into the thickness of the organ and divides the gland into separate lobules, lobuli. In the thickness of the gland, thin connective tissue layers, rich in blood vessels and nerves, form the supporting tissue of the thyroid gland - stroma, stroma. In its loops are follicles of the thyroid gland, folliculae glandulae thyroideae.

Fibrous capsule covers the outer capsule of the thyroid gland, which is a derivative of the fascia of the neck. With its connective tissue bundles, the outer capsule fixes the thyroid gland to neighboring organs: cricoid cartilage, trachea, to the sternum-hyoid and the sternum-thyroid muscles ; Part of these bundles (the densest) form a kind of ligaments that go from the gland to the nearby organs.

Three pencils are most well expressed: the middle ligament of the thyroid gland, fixing the capsule in the region of the isthmus to the anterior surface of the cricoid cartilage, and two, right and left, lateral ligament of the thyroid gland, fixing the capsule in the region of the lower medial sections of both lateral lobes to the lateral surfaces of the cricoid cartilage and the nearest To it cartilaginous tracheal rings.

Between the outer and inner capsules is a slit-like space, made of loose fatty tissue. It contains extraorganic vessels of the thyroid gland, lymph nodes and parathyroid glands.

The anterolateral surfaces of the thyroid gland are covered with the sternum-hyoid and the sternum-thyroid muscles, as well as the upper abdomen of the scapula-sublingual muscles .

At the site of the transition from the anterolateral surfaces to the posteromedial thyroid gland adjoins the neurovascular bundle of the neck (common carotid artery, internal jugular vein, vagus nerve). In addition, the posteromedial surface has a recurrent laryngeal nerve, tracheal lymph nodes are located here.

The lower sections of both, right and left, lobes reach the 5th-6th ring of the trachea.
The median surface of the gland adjoins the lateral surfaces of the trachea, pharynx and esophagus, and at the top - to the cricoid and thyroid cartilage.

The isthmus of the gland is located at the level of the 1-3rd or 2-4th ring of the trachea. Its middle section is covered only with fused pre-tracheal and superficial plates of the cervical fascia and skin.

The mass of the gland is subject to individual fluctuations and ranges from 30 to 60 g. In an adult, the longitudinal dimension of one lobe of the thyroid gland reaches 6 cm, the transverse part - 4 cm, the thickness - up to 2 cm.

Iron increases during puberty. Its dimensions may vary depending on the degree of blood filling; To old age in the gland developing connective tissue and its dimensions are reduced.

The thyroid gland produces thyroxine hormones , triiodothyronine, thyrocalcitonin and calcitonin, which regulate metabolism (calcium and phosphorus) in the body, increasing heat exchange and strengthening oxidative processes, take part in bone formation. In the tissues of the thyroid gland, there is accumulation of iodine.

The thyroid gland is rich in arterial, venous and lymphatic vessels. Its own arteries, blood supply to the parenchyma of the gland, anastomose with the vessels of neighboring organs. Venous blood flows into the wide venous plexus located under the capsule, the most developed in the region of the isthmus and the anterior surface of the trachea.

Innervation : nerves from the cervical nodes of sympathetic trunks, involved in the formation of plexuses around vessels suitable for iron; From the vagus nerves (nn. Laryngei superiores - r. Externi, n. Laryngei reсurrentes).

Blood supply : a. Thyroidea superior from a. Carotis externa, a, thyroidea inferior from truncus thyrocervicalis - a branch. Subclavia, sometimes a. Thyroidea ima from truncus brachiocephalicus or arcus aortae (less often from a, carotis communis or a. Subclavia). Venous blood flows out by vv. Thyroideae superiores, dextra et sinistra (fall into vv. Jugulares internae or vv. Faciales), vv. Thyroideae inferiores, dexlra et sinistra (flow into the vv. Brachiocephalica), vv. Thyroidea mediae (may fall into v. Brachiocephalica sinistra or in v. Thyroidea inferior). Lymphatic vessels follow the course of the arteries and flow into the anterior deep cervical (thyroid and paratracheal) and mediastinal (anterior) lymph nodes.