Human Anatomy - M.M. Kurepina, A.P. Ozhigova, A.A. Nikitina 2010

Internal Organs
System of Endocrine Glands (Endocrine System)
General Information

The human Endocrine System consists of ductless glands (Fig. 4.58). The Cells of these glands produce Hormones and secrete them into the Blood, Lymph, or tissue fluid. This is THE ORIGIN OF their name: endo — within, crino — secrete. Individual endocrine cells, which are not grouped together, are scattered throughout the walls of certain Organs (gastrointestinal tract, respiratory tract, urogenital organs). Together, they form the Cytology/cytology/65.html">Diffuse endocrine system.

Endocrine glands participate in all vital processes of the body. Hormones act on the GENETIC APPARATUS OF cells, affect all METABOLISM/4.html">Types of Metabolism, as well as growth, physical and mental development, and participate in the adaptation of The Human Body to environmental conditions. During the Embryonic period, hormones play an essential role in The formation of Organ Systems and the establishment of their Functions. At the same time, an excess or Deficiency of certain hormones leads to metabolic, growth, and developmental disorders. Aging is accompanied by a decrease in sex hormone secretion in both sexes, although this is more pronounced in women.

Functionally, the endocrine system is closely linked to The Nervous system; together, these two systems coordinate the functions of other organs and organ systems, which are often separated by considerable distances. A specific sequence is observed in The Development of endocrine and neuroendocrine interactions during ontogenesis. Following the formation and Differentiation of the endocrine organs, hormone Synthesis and Secretion begin. Next, hormonal links are established between the endocrine glands, and finally, neuroendocrine connections are formed, which are discussed in detail in physiology courses.

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Fig. 4.58. Endocrine glands:

1 — Pineal Gland; 2 — Pituitary Gland; 3 — Thyroid Gland; 4 — Paraganglia; 5 — Adrenal Glands; 6 — Pancreas; 7 — Testes

All endocrine glands are characterized by a highly developed Blood supply and lymphatic drainage. This facilitates the rapid entry of hormones into the bloodstream and lymph. The activity of endocrine glands is regulated by the Autonomic nervous system.

The endocrine system controls those bodily functions that require minutes or hours to initiate and regulate. This is because hormone-mediated information transfer is tens of times slower than neural transmission, which allows the body to respond immediately to functional changes and environmental factors.

Glands that develop from the branchial region of the embryonic foregut are referred to as branchiogenic glands. These include the thyroid, parathyroid, and Thymus glands.

In addition, the endocrine system is conventionally divided into central and peripheral glands. Central glands perform a regulatory function in relation to other glands. This group includes the pituitary gland and the pineal gland. In turn, their function is regulated by Neurons of the hypothalamic nuclei. Peripheral glands include the thyroid and Parathyroid glands, as well as the adrenal glands. There are also organs that combine endocrine and other functions. These include the pancreas, testes, Ovaries, and Placenta. The functions of most of these are controlled by Pituitary Hormones (Fig. 4.59).

Based on their origin, all endocrine glands are divided into three groups (Table 4.1).