The hypothalamus (from the Greek hypo, below and thalamos, cavity) is a gland in the brain, involved in the regulation of many functions of the body.

Located at the base of the brain under the thalamus, the hypothalamus is a gland divided into several independent nuclei, themselves made up of a set of nerve cells. The hypothalamus is connected to the pituitary gland, another gland in the brain, through the pitular stem to form the hypothalamic-pituitary axis¹.

Role of the hypothalamus. It is involved in many body functions such as body temperature, hunger², thirst, sleep cycles, the female menstrual cycle, sexual behavior or emotions³.

Functioning of the hypothalamus. It acts as a control center reacting according to various perceived stimuli: hormonal, nervous, blood, microbial, humoral, etc. In response to these factors, the hypothalamus synthesizes different hormones which will act either directly on the organs or on the pituitary gland which will in turn secrete other hormones¹.

Pituitary gland control and regulation. The hypothalamus secretes neurohormones, the liberins, which will act on the pituitary gland by regulating the secretion of hormones, the stimulins. These will stimulate other glands in the body such as the thyroid or the ovaries. The liberins, secreted by the hypothalamus, are in particular:

• Corticoliberin (CRF) which controls the secretion of corticotrophin (ACTH) leading to the synthesis of cortisol
• Thyroliberin (TRH) which controls the secretion of thyroid stimulating thyroid stimulating hormone (TSH)
• Gonadotropin releasing hormone (GnRH) which controls the secretion of gonadotropins (FSH and LH) that stimulate the ovaries
• Somatoliberin (GH-RH) which controls the secretion of somatotropin, growth hormone

Secretion of hormones. The hypothalamus secretes two hormones which will then be released by the pituitary gland into the blood:

• Vasopressin, an antidiuretic hormone, which acts in the kidneys to limit water loss
• Oxytocyne, which stimulates the contractions of the uterus during childbirth, as well as the mammary glands for breastfeeding

The hypothalamus also partially synthesizes dopamine, a precursor of prolactin and catecholamines (including adrenaline and norepinephrine).

Participation in the vegetative nervous system. The hypothalamus has a role within the vegetative nervous system, responsible for non-voluntary body functions such as regulating the heart rate or breathing.

Given the relationship between the hypothalamus and the pituitary gland, their pathologies are closely linked and result in dysfunction of the hormonal system².

Tumor. The hypothalamus can be affected by a tumor, causing the hypothalamic then hyophyseal secretions to stop. The symptoms are expressed according to the size of the tumor (headache, visual field disorders, neurological disorders) and hormonal deficit (fatigue, pallor, absence of periods).

Hypothalamic syndrome. An imbalance in the hypothalamic system can affect various body functions such as regulating internal temperature, disrupting thirst and hunger (5).

Hyperhydrose. Excessive sweating may be observed in case of hyperfunction of the body internal temperature control pathway, modulated by the hypothalamus.

Hormonal substitute / Hormone therapy. Hormonal therapy is often offered to counteract the dysfunction of the hypothalamus and / or pituitary gland.

Surgical treatment or radiotherapy. Depending on the tumor, surgery or radiation therapy may be needed.

Radiological examinations. A CT scan or MRI may be done to identify the origin of the hormonal dysfunction.

Medical analysis. Hormonal assays can be used to assess hormonal dysfunction.

The demonstration of the relationship between the secretion of hormones by the hypothalamus and the nervous system dates back to the 50s thanks to the work of Geoffrey Harris (6).