Diseases of the hypothalamus
The hypothalamus produces a variety of different hormones. Some of these hormones are called “releasing hormones”. In a hormonal control circuit, they act directly on the pituitary gland and stimulate the production of further hormones, which in turn act directly on the target organs or trigger further hormone production.
In return, there are the “inhibiting hormones”, which are also produced by the hypothalamus and inhibit the release of hormones from the pituitary gland and the periphery (at the target organs). The most important releasing hormones of the hypothalamus are CRH (corticotropin releasing hormone), TRH (thyrotropin releasing hormone), growth hormone releasing hormone (also known as somatotropin or STH) and GnRH (gonadotropin releasing hormone). CRH stimulates the production of ACTH (adrenocorticotropic hormone) in the pituitary gland.
The ACTH in turn acts on the adrenal gland, whereupon increased amounts of glucocorticoids, mineral corticoids and androgens are produced. Glucocorticoids, of which cortisol is the main representative, act mainly on the metabolism, with an increase in blood pressure and blood sugar, and on the immune system, with an anti-inflammatory effect. The main stimuli for the release of cortisol are stress and pain, but also low blood pressure or low blood sugar.
Mineral corticoids, such as aldosterone, regulate the salt and water balance of the body. Androgens, which are also produced in the adrenal gland, have an anabolic metabolism, with muscle and bone building. If sufficient androgens, mineralcorticoids or glucocorticoids have been produced by the body, they inhibit further secretion of CRH and ACTH from the hypothalamus and pituitary gland via negative feedback regulation.
This prevents too many hormones from being produced peripherally (in the adrenal gland). Another regulatory circuit is the formation of TRH. Via the TRH, the hypothalamus stimulates the formation of TSH (thyroid-stimulating hormone) in the pituitary gland, which in turn acts directly on the thyroid gland and leads to an increase in thyroid hormones (T3/T4) there.
Stimuli for the formation of TRH are mainly strong cold and stress. The thyroid hormones T3 and T4 act mainly on the circulation and metabolism, and lead to a general increase in the basal metabolic rate. They also increase the breakdown of fats, proteins and carbohydrates, and raise heart rate, temperature and blood pressure.
To prevent overproduction of thyroid hormones, there is also a negative feedback mechanism in which the formation of T3 and T4 prevents the further formation of TSH. The growth hormone releasing hormone (also known as somatotropin or STH), which is produced in the hypothalamus, plays a central role in growth and regulation of the metabolism. In turn, it stimulates the production of growth hormone (synonym: growth hormone) in the pituitary gland, which in turn acts on cells in the liver to produce a hormone (IGF-1) that promotes growth during childhood and, later in adulthood, primarily results in anabolic metabolic regulation.
This mechanism is inhibited by the hormone somatostatin, which is also produced in the hypothalamus. Via the GnRH (gonadotropin-releasing hormone), the hypothalamus stimulates the release of the two hormones LH and FSH in the pituitary gland. FSH and LH have a central role in the formation of sex hormones and the development of the gonads.
In women, FSH causes the maturation of egg cells and the formation of estrogens, and in men, the maturation of sperm. LH promotes ovulation and the formation of estrogens and progesterone in women, and testosterone in men, with development of the respective sexual characteristics during puberty. This control cycle is also subject to a negative feedback mechanism.
The most important inhibiting hormones produced in the hypothalamus are, for example, somatostatin, which inhibits the release of growth hormone in the pituitary gland, and dopamine, which inhibits prolactin. Other hormones that are produced in the hypothalamus and act directly on the target organ (for example, kidney, uterus, breast) are for example ADH, which, in addition to the mineral corticoids, also regulates the salt and water balance of the body via the kidneys, oxytocin, which is secreted especially during pregnancy to induce labor, and prolactin, which leads to milk secretion in the female mammary glands. Disturbances in the respective circulatory systems usually lead to serious diseases, which are either associated with a deficiency or an excess supply of hormones.The consequences are usually developmental disorders, infertility or a lack of adaptation of the body to various environmental situations and stresses.
