Endocrine Tissue

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Production and release of hormones

The endocrine tissue is a complex of various glands that produce hormones involved in bodily processes such as metabolic processes, water and electrolyte balance, maturation, growth and reproduction. Endocrine tissue includes the hypothalamus, pituitary gland, pineal gland, thyroid gland, parathyroid gland, adrenal gland, gonads and pancreas. Hormones are mostly distributed via the bloodstream. In order for the hormones to ultimately act on the target organ, the target organs each have specific receptors. Some hormones act paracrine in the immediate vicinity or within the secreting gland, others unfold their effect autocrine by direct feedback to the hormone-producing gland.

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Hypothalamus

the coordinating unit

The central coordinating unit of the organizational units (regulatory circuits) of the endocrine system is located in the hypothalamus. In the hypothalamus, the production of control and effector hormones takes place, whereby the control hormones are further subdivided into releasing and inhibiting hormones. These hormones include: Anti-diuretic hormone (ADH), Corticoliberin (CRH), Gonadoliberin (GnRH), Somatoliberin (GHRH), Somatostatin (GHIH), Prolactin-releasing hormone (PRH), Dopamine (PIH), Thyroliberin (TRH).

Pituitary gland

regulated release of hormones from the hypothalamus

The pituitary gland located near the hypothalamus and is composed of the fundamentally different adenohypophysis (anterior pituitary) and neurohypophysis (posterior pituitary). In the adenohypophysis, the release of glandular hormones (ACTH, TSH, FSH and prolactin) and glandular hormones (growth hormones), which are previously produced in the hypothalamus, is regulated. This hormone release is regulated by releasing hormones (liberins) and inhibiting hormones (statins). The neurohypophysis is the storage site for the hormones oxytocin and ADH produced in the hypothalamus and regulates the release of these hormones into the bloodstream as required.

Pineal gland

light-sensitive hormone secretion

The pineal gland is primarily not a gland, but a hormone-producing light-sensing organ that is involved in the sympathetic nervous system and receives information about brightness from the retina via photoreceptor cells. Depending on the light impulse, the pineal gland secretes melatonin and thus affects the sleep-wake rhythm and other time-dependent rhythms.

Thyroid and parathyroid gland

growth promotion, intervention in metabolism and regulation of calcium levels

The thyroid gland (glandula thyroidea) is a butterfly-shaped organ located just anterior to the trachea below the larynx, with the four parathyroid glands located posteriorly. The thyroid gland absorbs iodine from the blood and uses it to produce the thyroid hormones thyroxine (T4) and tetraiodothyronine (T3), which are stored and released when needed. Furthermore, the thyroid gland is responsible for calcitonin production, which promotes calcium incorporation into the bones as well as reduces its resorption from food (lowering calcium levels). The parathyroid glands are epithelial corpuscles about 5 mm in size that produce parathyroid hormone (PTH), which contributes to the regulation of calcium and phosphate metabolism.

Adrenal glands

regulation of blood pressure, electrolyte balance and stress response

The adrenal glands consist of the two functional units adrenal medulla and cortex and is located at the upper pole of the kidneys. Their main function is the production of glucocorticoids, mineralocorticoids and sex hormones, which are released after stimulation by the hormones of the pituitary gland (except mineral corticoids). The glucocorticoids inhibit the immune defense as well as inflammatory processes and contribute to the provision of energy by fat and protein breakdown and glycogenesis. Mineral corticoids have a paracrine effect in the kidney and influence blood pressure through reabsorption of water and sodium and increased calcium secretion. Furthermore, androgens such as estrogens and progestin and catecholamines such as epinephrine and norepinephrine are produced in the adrenal gland.

Gonads

regulation of sexual development

Under gonads the exocrine units testis and ovaries are summarized. The hormonal action of the hypothalamus and pituitary gland (FSH and LH), causes a change in the ovary, whereby the oocytes maturing within it increasingly produce estrogen until ovulation. If LH secretion occurs, ovulation is ultimately triggered and the female sexual organs are prepared to receive sperm. Once ovulation is complete, a corpus luteum develops, which produces progesterone and another form of estrogen while inhibiting the hypothalamus and pituitary gland. The male testis, like the ovary, is controlled by hormones (FSH and LH) from the pituitary gland. It contains the Leydig intermediate cells, which produce the male sex hormone testosterone, and the Sertoli cells, which produce inhibin and an androgen-binding protein (ABP) and are important for spermatogenesis.

Pancreas

provision of digestive enzymes

The pancreas contains endocrine cells, which are grouped together as an islet organ. These consist of individual islets of Langerhans, which produce the hormones insulin and glucagon, among others. Insulin secretion leads to lowers blood glucose levels by storing sugar in the liver, fatty tissue and skeletal muscle, and by directly breaking down the sugar present while simultaneously producing energy (glycolysis).

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