What is the hypothalamus?
The hypothalamus is an area of the diencephalon. It consists of nerve cell clusters (nuclei) that act as switching stations for the pathways leading to and from other parts of the brain:
Thus, the hypothalamus receives information from the hippocampus, amygdala, thalamus, striatum (group of basal ganglia), the cortex of the limbic system, the midbrain, rhomboid brain and spinal cord.
Information flows from the hypothalamus to the midbrain and thalamus as well as to the neurohypophysis (posterior lobe of the pituitary gland).
What is the function of the hypothalamus?
The hypothalamus is the mediator between the endocrine and nervous systems: it receives information from various measuring stations in the body (e.g. about blood sugar, blood pressure, temperature). It can regulate these parameters as required by releasing hormones.
For example, the hypothalamus controls body temperature, the sleep-wake rhythm, the feeling of hunger and thirst, the sex drive and the sensation of pain.
The hypothalamus hormones can be divided into three groups:
Effector hormones
Both hormones are synthesized in the hypothalamus nuclei and then transported to the posterior lobe of the pituitary gland, from where they are released into the systemic circulation.
Control hormones
The second group of hypothalamic hormones are control hormones, whereby a distinction is made between releasing and inhibiting hormones:
The hypothalamus uses releasing hormones to stimulate the pituitary gland to synthesize and secrete various hormones. For example, gonadotropin-releasing hormone (GnRH) triggers the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
The hypothalamus uses inhibiting hormones to slow down the secretion of pituitary hormones. For example, the prolactin-releasing inhibiting hormone (PIH) inhibits the secretion of prolactin.
Other hormones
In addition to effector and control hormones, the hypothalamus also has a number of other hormones (neuropeptides). Together with the two other groups of hypothalamic hormones, these influence the function of the anterior pituitary gland or act as communicators between the hypothalamus and other areas of the brain.
These other neuropeptides of the hypothalamus include, for example, enkephalins and neuropeptide Y.
Regulatory circuits ensure order
Example: Thermoregulation
In addition to many other control circuits, thermoregulation is important for the body to maintain a core temperature of around 37 degrees Celsius. This must – within certain limits – always be constant. To achieve this, the body has “sensors” in the skin and organs – free nerve endings of sensitive nerve cells. Their information is transmitted to the thalamus and then on to the hypothalamus.
If the core body temperature drops, a control circuit for temperature regulation is triggered. The hypothalamus releases the hormone TRH (thyrotropin-releasing hormone). TRH stimulates the anterior pituitary gland to release TSH (thyroid-stimulating hormone).
TSH in turn regulates the production of the thyroid hormone thyroxine (T4). This enters fatty tissue and skeletal muscles, where it is converted into triiodothyronine (T3). T3 increases the basal metabolic rate, boosts the supply of energy from the liver and increases the heart rate – resulting in an increase in temperature.
If the core body temperature rises, the hypothalamus lowers the sympathetic tone, which dilates the vessels in the periphery and promotes sweat secretion – resulting in the body cooling down.
Where is the hypothalamus located?
What problems can the hypothalamus cause?
The eating center and the satiety center are located in the hypothalamus. In the case of disorders in the eating center, which can be genetic or psychogenic, food is no longer absorbed – those affected lose weight. If, on the other hand, the satiety center is disturbed and the eating center is permanently active, hyperphagia develops, i.e. excessive food intake with the development of obesity.
A pituitary adenoma (benign tumor of the pituitary gland) can impair the function of the pituitary gland itself as well as that of the hypothalamus. As a result, either too many or too few hormones are produced. For example, acromegaly (enlargement of the nose, chin, fingers and skull bones) is caused by an overproduction of STH, while Cushing’s disease is caused by an overproduction of cortisol.
Tumors that grow in the area of the hypothalamus are very rare and lead to hypothalamic syndrome, for example, due to changes in hormone production. It is characterized by severe obesity and short stature.
