What is hypothalamic gland
Control centers for hormones
In addition to the effector hormones, the hypothalamus, or more precisely the small-cell nuclei, also produces a number of control hormones that represent the other way in which the hypothalamus and pituitary interact. Depending on their function, they are divided into two groups. The releasing hormones (RH), also called liberine or reline, increase the production and release of hormones in the anterior pituitary gland. The release inhibiting hormones (IH) or statins have the opposite effect: They slow down the release.
The control hormones reach the adenohypophysis via a portal vein system, i.e. by blood. These include, for example, the thyrotropin-releasing hormone (TRH), whose pulsatile release causes the release of thyroid-stimulating hormone (TSH), but also of prolactin. TSH in turn stimulates the thyroid gland to produce and release thyroxine (tetraiodothyronine, T4) and triiodothyronine (T3). These hormones influence the energy metabolism, thermogenesis, organ development and growth in length.
The gonadotropin-releasing hormone promotes the release of the two sex hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the adenohypophysis.
Functions of the pituitary gland
The two parts of the pituitary not only perform different tasks. They also differ morphologically. The adenohypophysis is a gland derived from the oral ectoderm. It is a part of the oral cavity that has attached itself to the posterior lobe of the pituitary gland in the course of embryonic development. However, this is part of the central nervous system. The neurohypophysis consists of nerve tracts that pull down from the hypothalamus. Historically, it evolved from the neural ectoderm.
The neurohypophysis stores and releases two hormones that have an effectoral effect. Oxytocin promotes the contraction of the uterine muscles during childbirth and the expression of milk by contracting the myoepithelium in the breast during breastfeeding (see cuddle hormone oxytocin). Vasopressin acts on the distal tubules and collecting ducts of the kidney and increases water retention there. It also has a vasoconstrictor effect on the vessels of the skin and the skeletal muscles (see vasopressin can do more).
In contrast, the anterior pituitary itself produces hormones, albeit under the control of the hypothalamus. This includes three hormones that also act effectorally, i.e. directly on the target organs. On the one hand there is the growth hormone (somatotropin), which determines the length growth before puberty, promotes the growth of the internal organs and influences the metabolism (see also growth signals from the switching point). On the other hand, the adenohypophysis produces the prolactin, which stimulates the breast to grow and promotes milk production (see too much prolactin is unhealthy).
The third adenohypophyseal effector hormone is melanocyte-stimulating hormone (MSH). It influences the formation of melanin in the melanocytes and thus the skin pigmentation.
In addition, the adenohypophysis also produces glandotropic hormones that act on other endocrine glands. These include the thyroid-stimulating hormone, which stimulates the thyroid gland to produce hormones, and the adrenocorticotropic hormone (ACTH), which stimulates glucocorticoid production in the adrenal cortex.
The follicle-stimulating hormone and the luteinizing hormone cause, among other things, the formation of estrogen and testosterone in the gonads.
Under strict control
Corresponding to the different functions of the anterior and posterior lobes of the pituitary gland, hormone secretion is regulated differently in the two parts. The stimulation of certain receptors in the hypothalamus leads to the release of neurohypophyseal hormones.
The secretion of the adenohypophyseal hormones, on the other hand, is regulated in a somewhat more complicated manner. On the one hand, it is subject to the control of the control hormones of the hypothalamus, whereby there is usually a release-promoting and a release-inhibiting hormone. On the other hand, the peripheral levels of the hormones produced by the affected glands act as a feedback on the hormone production. For example, a high cortisol level in the periphery can inhibit the release of ACTH. But positive feedback is also possible: high estradiol levels stimulate the release of FSH and thus trigger ovulation.
In addition, the hypothalamus secretes regulating neurotransmitters and neuropeptides, which are often released as cotransmitters to the control hormones. The hypothalamus-pituitary system is therefore strictly controlled and finely regulated. If it is out of balance, certain hormones are either not released at all or in too large quantities. This can have dramatic consequences for the organism.
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