Thymus. structure

Thymus gland (thymus), thymus, unpaired. It distinguishes two closely adjoining and connected with one another loose connective tissue of the lobe - the right lobe, the lobus dexter, and the left lobe, the lobus sinister. Sometimes both parts are divided by the intercalary part. Rarely 3-4 parts are observed. The lobes of the gland are asymmetric, elongated in length. Anterior surface convex, posterior concave.

The lower, most expanded part of the gland was called the base of the thymus gland .

The bulk of the thymus gland lies in the anterior mediastinum, and its apex is located in the upper mediastinum, behind the handle and upper body of the sternum , in the region of the so-called triangle of the thymus gland.

The upper sections of the gland with its posterior surface adjoin the trachea, the anterior one at the site of attachment of the sternum -thyroid muscles . The posterior surface of the rest of the thymus gland adjoins the large blood vessels (to the superior vena cava, the brachiocephalic veins, the arch of the aorta with the arteries draining from it), to the pericardium, and the edges of the gland adjoin the mediastinal pleura.

The upper parts of the gland, the most narrowed, are called the tip of the thymus gland. They can go beyond the upper mediastinum and in the newborn reach the thyroid gland , occupying the space above the jugular notch. The lower borders of the gland reach the level of the cartilage of the 3rd rib .

The structure of the thymus gland.

Thymus gland gray-pink color, with age becomes yellowish due to the prevalence of fat in it.

The weight of the gland in a child of 2 years reaches 20 g, by 15 years is 30-40 g, then the period of involution begins; Gland decreases sharply and by 25-30 years it reaches 25 g, and by the age of 70 - 6 g.

The longitudinal size of the gland in the newborn is up to 5 cm, the transverse dimension is from 2 to 3 cm and the anteroposterior dimension is 8 to 10 mm.

The gland is covered with a thin connective tissue membrane, which forms septa between individual thymus lobuli, lobuli thymi. The parenchyma of the lobules consists of the cortex of the thymus, cortex thymi, located on the periphery, and the medulla thymi, medulla thymi, located in the center of the lobules. Both cortical and cerebral matter consists of a network, the loops of which are made by lymphocytes.

A special feature of the brain substance is the presence in it of special concentric bodies.

The gland capsule is surrounded by fatty and loose fiber, fixing the gland to adjacent organs and vessels; In its thickness, sometimes lie the anterior mediastinal lymph nodes. Sometimes there are isolated nodules, the so-called accessory nodules of the thymus gland, nodi thymici accessorii.

The thymus gland is the central organ of immunogenesis. It produces a hormone-like substance called thymosin, which increases the number of lymphocytes and enhances the immune response. Timozin participates in adaptive reactions of the body, as well as in the processes of growth and formation of the skeleton.

Innervation: branches from nn. Vagi, from plexus thoracicus internus (follows rr. Thymici - branches of n. Thoracica interna). In the formation of the plexus thoracicus, the branches of the four lower cervical spinal nerves and the three cervical sympathetic nodes participate. To the capsule of the thymus gland the trunks from the diaphragm nerves and from the cervical loops are suitable.

Blood supply: rr. Thymici from aa. Thoracicae internae, rr. Thymici from aa. Thyroideae inferiores, pericardiacophrenicae, phrenicae superiores (sometimes from aa., Thyroideae superiores and trunci brachiocephalici). Such an abundance of arterial sources is typical for children and adolescents. Venous blood flows along large veins and one venous trunk, which empties into v. Brachiocephalica sinistra, and from small veins - in vv. Thoracicae internae, thyroideae inferiores, pericardiacophrenicae, phrenicae superiores (sometimes in vv. Jugulares). Lymphatic vessels flow into the mediastinal lymph nodes.