Thyroid gland

The thyroid is a gland of internal secretion, secreting iodine-containing hormones, thyrocalcitonin.

thyroid gland
Thyroid gland: 1 - pyramidal share; 2 - the left lobe; 3 - the isthmus of the thyroid gland; 4 - inferior thyroid artery (top) and Vienna; 5 - the inferior thyroid artery (right - Vienna); 6 - the right proportion; 7-superior thyroid artery (below) and Vienna.

Anatomy. The thyroid gland is located at the front of the neck. It consists of two lobes and the isthmus (Fig). Sometimes from the neck up departs pyramidal share. The thyroid gland has a fibrous capsule. Using ligaments capsule thyroid gland is fixed to the cricoid cartilage of the larynx and trachea, which determines the offset of cancer swallowing together with the larynx and trachea. The blood supply of the thyroid gland is made of upper and lower thyroid arteries, veins of the thyroid gland fall into the internal jugular and General facial veins.
In some cases, there may be additional (at the bottom) thyroid artery and vein. Lymphatic vessels are directed to the deep cervical lymph nodes. Innerviruetsya thyroid branches stray nerves and sympathetic trunks.
The parenchyma of the thyroid gland consists of follicles of the oval form, the cavity which is filled with colloid (protein-mycopolysaccharide mass, the main of which is a specific iodine-containing protein thyroglobulin). The wall consists of a single follicle epithelium, lying on the basal membrane.
Physiology. The thyroid gland secretes in the blood three hormone: two iodine - thyroxine (tetrajodtironina) and triiodothyronine, and the third containing no iodine - thyrocalcitonin. Iodine enters the body with food and water; thyroid concentrates from blood iodine, iodine, which is used in the synthesis of hormones. Iodine-containing hormones are produced in the epithelial cells of the follicles, whence arrive in colloid; thyrocalcitonin is produced in majolicaware epithelial cells.
Thyroxin and triiodothyronine are unidirectional, however, the slow action of the first, second, a faster and more active. Both of these hormones have an impact on the consumption of oxygen and involved in the regulation of the metabolism of proteins, fats and carbohydrates, as well as water exchange. From their activity depend essentially biological processes: the growth and development of the organism and the differentiation of tissues. Thyrocalcitonin regulates the exchange of calcium in the body and preventing its resorption of bone tissue, promotes its disposal.
The activity of the thyroid gland is regulated by the nervous system, and the pituitary gland. The hypothalamus produces neurosci (thyrotropinreleasing factor), regulates the secretion tireotroponogo pituitary hormone; the latter regulates the activity of the thyroid gland.

The thyroid gland (glandula thyreoidea, s. corpus thyreoideum) - gland of internal secretion, synthesizing and nakaplivaetsya iodine-containing hormones under control of which are important physiological functions of the organism (growth, development of the body, the metabolic rate, metabolism).
       Embryology
The thyroid gland develops from ventral pharyngeal wall Department of the colon to the end of the 1st month. fetal life as thickening of the ectoderm. From the top of this thickening begins to grow thin cord (future thyroglossal duct), divided by the middle of the 2nd month of fetal life on the two side growth. Last, growing, form side lobe and the lower part of the germ of a thyroid gland is saved as an isthmus between them. Obliteration thyroglossal duct is on the 2nd month of fetal life, but sometimes a part of him may be saved and be a source of incremental development of the thyroid glands. The epithelium of the lateral lobes of the thyroid gland grows in the form of cellular fibers with subsequent differentiation in the follicles. The first follicles appear in embryo to the 4th month. fetal life, the signs secretion are identified earlier. The development of thyroid ends to 8-9-th month. fetal development.
Anatomy


Fig. 1. Pyramidal slice and incremental thyroid gland.

The thyroid gland is located at the front of the neck (printing. table, Fig. 1)has a horseshoe or Crescent shape and consists of two lateral lobes and the isthmus. The isthmus is adjacent to the trachea front, side lobe side (right and left). Sometimes there is impermanent pyramidal slice (Fig.1). Occasionally the isthmus is missing and side lobe related connective tissue jumper. The form and the sizes of the shares subject to considerable variations (Fig. 2). Women thyroid more than men. Its sizes are increased during pregnancy. The top border cancer is the outer surface of the thyroid cartilage, lower - 5-7 ring trachea. The thyroid gland has external and internal connective tissue capsule (Fig. 3). Internal covers iron, outer forms ligamentous apparatus, fixing the thyroid gland to the trachea and larynx. Between the sheets capsules are vessels.

abnormalities of the thyroid gland
Fig. 2. Options for the form, and abnormalities of the thyroid gland (Marshall).
where is the thyroid gland
Fig. 1. The topography of the thyroid gland (its relation to fascia, muscles and organs of the neck). Fig. 2 and 3. The blood vessels of the thyroid gland (Fig. 2 - front view, Fig. 3 - back);

1 - v. brachiocephalica dext.;
2 - v. thyreoidea ima;
3 - plexus thyreoideus impar;
4 - a. subclavia;
5 - truncus thyreocervicalis;
6 - a. thyreoidea inf.;
7 - v. thyreoidea inf.;
8 - v. jugularis int.;
9 - v. thyreoidea sup.;
10 - a. thyreoidea sup.;
11 - a. carotis ext.;
12 - a. carotis int.;
13 - v. thyreoidea media;
14 - v. brachiocephalica sin.;
15 - plexus pharyngeus (venosus).
the blood vessels of the thyroid gland

The thyroid gland is richly supplied with blood vessels: two upper (branch of the external carotid artery), two lower and one (non-permanent) unpaired thyroid arteries (printing. table, Fig. 2 and 3). Superior thyroid artery divides into three branches: the front and outer rear. Last anastomosed with inferior thyroid artery. Inferior thyroid artery is divided into three target branch: the lower, rear, deep. Venous system developed more powerful than the blood, and is also rich in anastomoses.
The lymphatic system of the thyroid gland presents capillaries, superficial and deep lymphatic vessels. Lymph drainage is carried out in the jugular lymph trunk. The last level of VII cervical vertebra flows into the left subclavian vein of, or in connection with its internal jugular vein.
Thyroid innerviruetsya branches of wandering, sympathetic, language-pharyngeal and hypoglossal nerve (Fig. 4)which are interconnected by anastomoses.

capsules thyroid gland
Fig. 3. Internal and external (passing in the fascial sheath neurovascular bundle) capsules of the thyroid gland.
the nerves of the thyroid gland
Fig. 4. The nerves of the thyroid gland (polyhema):
1 - n. vagus;
2 - n. laryngeus recurrens (with branches to gland);
3 - n. laryngeus sup. (with branches to gland);
4 - gangl. cervicale sup.;
5 - truncus sympathicus;
6 - sympathetic plexus on a. thyreoidea sup. (plexus tliyreoideus sup.);
7 - gangl. cervicale medium (with branches to gland);
8 - sympathetic plexus on a. thyreoidea inf. (plexus thyreoideus inf.).

Histology
The parenchyma of the thyroid gland consists of follicles are round or oval in shape. The average value of their 40-50 MK. The follicle wall presents a single layer of epithelium, located on the basal membrane, which is intimately connected with capillary endothelium. The height and shape of the epithelium vary depending on its functional activity. There are two types of follicular epithelium: cubic and prismatic. In apical departments of the epithelial cells, have membrane, forming the papillary ridges in the lumen of the follicle. Kernel follicular epithelium bright, round or oval. Cavity follicles filled with colloid - protein-mycopolysaccharide mass, the main of which is a specific iodine-containing protein thyroglobulin. In the cytoplasm of follicular epithelium well developed endoplasmic network, which is a system tubules, vacuoles, tanks, limited cytoplasmic membranes. The form of networks is changing in connection with the functional activity of the cell. On the outer surface of cytomembrane are ribosomes, the protein-rich and RNA. Ribosomes are in the form of rosettes, or spirals. In apical part and in the field kernel follicular epithelium are the mitochondria. Their shape is diverse - from round to rod-shaped. The size and number of mitochondria increase with active secretory activity of the thyroid gland. Above the kernel is the Golgi apparatus, with a net structure and strongly increasing in the period secretory activity.
In the cytoplasm of follicular epithelium contains ascorbic acid, RNA, phosphatase (acid, alkaline), codeprivate, succenderunt, cytochrome oxidase and other enzymes. Among the epithelial cells in the wall of the follicles are occasionally found parafollicular bright cells and cells of Langendorf with dark cytoplasm. Both arise from cells follicular epithelium and represent one of the morphofunctional stages in a single cycle of his transformation. Parafollicular cells characteristic of the increase and expansion of the network of Golgi apparatus, marginal activity phosphatases, low content neutral mucopolysaccharides, histidine, RNA.
The growth of the thyroid gland at the expense of formation of follicles as in the centers of cambial majolicaware parenchyma and intrafollicular the pads. The latter arise from the proliferation of the epithelium in the lumen of the follicles. Secondary follicles crayons, their cells retain the capacity to produce colloid.