The hypothalamus is a comparatively small but vital tissue area of the autonomic nervous system. The hypothalamus is used to regulate the production of various hormones that, among other things, stimulate the pituitary gland.
What is the hypothalamus?
The brain and hypothalamus are among the most complex structures in our human body. Many processes are currently not fully understood. The hypothalamus belongs to the diencephalon (midbrain) and coordinates blood pressure and water and salt balance within the autonomic nervous system as a higher-level control center. This important control center of the human organism is located below (“hypo”) the thalamus, the largest tissue structure of the diencephalon. The hypothalamus can be divided into an anterior, low-medullary section and a posterior, high-medullary section. While the anterior section is thought to be responsible for autonomic functions and acts as an interface between the nervous and intrasecretory systems, the posterior hypothalamus is classified as belonging to the limbic system.
Location, anatomy, and structure
The hypothalamus is demarcated superiorly from the dorsal thalamus by a shallow furrow within the wall of the 3rd ventricle. The hypothalamic nuclear areas are located in the diencephalic walls below this furrow. Frontally, the optic chiasm (optic nerve junction) is located at the base, behind which the infundibulum (funnel-like structure) descends on the diencephalic floor. At the end of the infundibulum is the pituitary gland. At the more posterior transition to the midbrain, the corpora mamillaria protrude from the hypothalamic floor on both sides. The posterior hypothalamus, which belongs to the limbic system, consists primarily of the corpora mamillaria and is traversed by large, medullary nerve fibers (axons of the fornix) (medullary hypothalamus). In contrast, thinner nerve fibers run through the anterior hypothalamus (medullary hypothalamus). This can also be divided into many individual nuclear areas (several dozen) that belong to the autonomic system. In addition, the anterior hypothalamus contains a large number of receptors to which hormones synthesized by other endocrine glands can bind.
Function and Tasks
As an endocrine gland and the receptors and nerve fibers it contains, the anterior, medullary hypothalamus serves as a kind of interface or mediator between hormonal and nervous regulation of various bodily functions. Thus, the nucleus suprachiasmaticus, located above the optic nerve junction, generates the internal clock and the individual day-night rhythm via direct inputs from the retinal ganglion cells, through which information from the environment (including time of day) is delivered. The supraoptic nucleus as well as the paraventricular nucleus, located in the ventricular and optic tracts, respectively, represent other important hypothalamic nuclei. Here, endocrine neurons (glandular neurons) produce hormones important to the organism, such as ADH (antidiuretic hormone) and oxytocin. ADH has a reducing effect on the amount of urine excreted, which also regulates the feeling of thirst. Oxytocin is a hormone that triggers contractions at the end of pregnancy and is released in greater quantities during orgasm. Furthermore, oxytocin provides a sense of trust and closeness. In the area of the opening of the infundibulum, the so-called tuber nuclei are located, which are also endocrine glands that synthesize inhibitory and stimulatory hormones such as dopamine and somatostatin or gonadotropin-releasing hormones (GnRH), thyrotropin-releasing hormones (TRH), corticotropin-releasing hormones (CRH) and growth hormone-releasing hormones. The infundibular nucleus and dorsomedial nucleus regulate food intake and metabolism. Axons draining from the hypothalamus influence internal organ function via motor neurons.
Diseases, ailments, and disorders
The function and action of the hypothalamus may be affected by various benign (benign) and malignant (malignant) diseases or tissue changes. If a disease correlates with a change in the production of a hormone produced in the hypothalamus, it is usually named after the affected hormone.For example, if the supraoptic nucleus and correspondingly the production and secretion of antidiuretic hormone (ADH) is impaired as a result of traumatic events, hemorrhage, tumors, or cerebral inflammation, diabetes insipidus (ADH deficiency) or Schwartz-Bartter syndrome (ADH excess) may manifest. Long-term glucocorticoid therapy may condition CRH deficiency, which can lead to glucocorticoid deficiency and then adversely affect carbohydrate, protein, and lipid metabolism, as well as salt and water balance. Changes in hypothalamic tissue structures or malignant tumors of other organs can also affect CRH production and cause Cushing’s syndrome (CRH excess). Accidents, radiation therapy, tumors or surgery can also lead to a hypothalamic dopamine deficiency via tissue changes and correspondingly to a prolactin excess (hyperprolactinemia) or a TRH deficiency (hypothyroidism). In addition, a so-called craniopharyngeoma (benign brain tumor), which presses on the hypothalamus and pituitary gland as it grows in size, can damage the tissue structures of the hypothalamus and impair its functions, especially hormone production.
