Endocrine glands. development and age characteristics of the endocrine glands

DEVELOPMENT AND AGE FEATURES endocrine glands.

Endocrine glands have different embryological origins, as evolved from different primordia. On the basis of genetic characteristics, they can be divided into five groups. So, from the endoderm develop thyroid, parathyroid, thymus gland and endocrine pancreas; from the mesoderm - adrenal cortex and gonads of the endocrine; from the ectoderm - the pituitary gland, pineal gland, the adrenal medulla and chromaffin body.

Thyroid refers to branchial group. It develops from the epithelium of the pharyngeal gill department of primary cancer, posterior to the rudiment of language. Blind hole tongue, which is a place bookmarks epithelial bud thyroid gland, is the residue of overgrown schitoyazychnogo flow. Last there in the period of embryonic development in the pyramidal process and heals within 4 weeks of intrauterine life. Neonates weight of about 2 g gland, it increases with the growth of the whole body, with the most intense during puberty and the adult reaches 40-60, the thyroid gland is located in the newborn is relatively high: it isthmus reaches the lower edge of the cricoid cartilage at the top and 5- th tracheal ring at the bottom. Form characteristic gland of an adult, it takes only 5-6 years of life.

Parathyroid glands (branchial group) develop a thickening of the epithelium of the 3rd and 4th branchial pockets. Newborns are very closely related to the thyroid gland, so they are difficult to detect. Most active parathyroid glands observed in children aged 4-7 years. With age, their size increases and the mass of 40-50 mg.

Thymus (branchial group) develops from the endoderm area 3rd gill pocket and is limfoepitelialnogo body. The largest size it reaches neonates and particularly in children aged 2 years; from now until puberty, it increases slightly. Further gland involution occurs, it is developed with a plurality of connective tissue fat cells: breast parenchyma is as small islands. In rare cases in adults stored iron (so-called status thymicolymphaticus). The weight of the thymus gland in the newborn varies from 10 to 15 g, and the end of puberty is 30 In puberty increases the amount of fat and connective tissue and the cortex and medulla becomes much less.
The pancreas is laid in the form of two rudiments endodermal epithelium of the duodenum wall - dorsal and ventral protrusions that are fused into a single body by the end of the 2nd month of intrauterine life. In the interior of the rudiments of the epithelium forms strands, turning into the tube, and of the epithelium lining them formed glandular tissue.

The endocrine part of the pancreas - pancreatic islets - develop from the endoderm, mainly dorsal bud, and the formation of islets continues after birth. Pancreatic islet cells are differentiated before the cells of the exocrine pancreas, despite the fact that they are laid simultaneously. The size of the islets with age reaches 0.1-0.3 mm.

The adrenal glands are composed of the cortex and medulla. Cortex develops from the mesoderm, the medulla appears later and is derived from the ectoderm. The child first year of life cortex dominates the brain, adult, and both are equally developed; old people, on the contrary, the cortex is almost twice less than cerebral. Newborn weight of both adrenal approximately 7 g and increased to 6-8 months .; increase in adrenal weight continues to 30 years.

Paraganglia (chromaffin body) develop from the ectoderm. In the embryo of 16-17 mm are presented in the form of two types of cells - and simpatoblastov hromaffinoblastov; the first form of sympathetic nodes, the latter are involved in the formation of chromaffin bodies - paraganglia. The greatest of them reach to 1 - 1.5 years of life. For 10-13 years, almost all paraganglia regress.

The sex glands - the testes and ovaries - originally laid the rudiments of how indifferent gonads. They are laid out in the mesodermal germ epithelium of the body cavity on the inner surface of the primary kidney. In the future, these glands begin to secrete hormones that affect the gradual formation of secondary sexual characteristics.

The male sex gland - testicle - hormones produced by interstitial cells, the number of which in the first half of intrauterine life is significantly increased, then decreases slightly. During puberty their number increases again.
The female gonads - ovaries - hormones produced by not only the interstitial cells, and granular layer of mature follicles. recent growth begins before puberty under the influence of gonadotropin-releasing hormone produced by the anterior pituitary gland.

Anterior pituitary (neurogenic group) develops from the epithelial walls of the dorsal protrusion oral bay as the pocket towards the bottom surface of the brain, in the bottom wall of the ventricle III where joins the posterior pituitary future. Rear share develops later the front of the funnel process, processus infundibuli, diencephalon and later joins the anterior lobe. A newborn pituitary often triangular. Its vertical dimension of 4 mm, longitudinal - 7.5 mm, transverse - 8.5 mm; weight 0.125 g; posterior lobe of the age of 10 years is significantly inferior to the value of the anterior lobe. adult pituitary weight reaches 0.5-0.6 g

The pineal gland (neurogenic group) develops from the area in the diencephalon epithalamus, epithalamus, a small protrusion, in which further grow into receptacles arranged inside a system of tubes surrounded by mesenchymal elements. For 7 years of life differentiation of epiphysis ends. Newborn epiphysis following dimensions: length 3 mm, width 2.5 mm, thickness 2 mm; birth weight of 0.7 g; to 6 years of life of its weight becomes equal to the mass of the pineal gland of an adult; maximum development of the iron reaches 14 years of life.