The hypothalamus is a part of the diencephalon composed of several small nuclei that have different physiologic functions. One of the main functions of the hypothalamus is to maintain homeostasis by controlling the endocrine and autonomic functions; nevertheless, it participates in other functions such as body temperature regulation, appetite, and weight, childbirth, growth, breast milk production, sleep-wake cycle, sex drive, emotions, and behavior. A disorder of the hypothalamus can cause different signs and symptoms, depending on the particular affected area. Clinical manifestations vary, depending on the affected hypothalamic nuclei and their functions. Certain signs and symptoms can be traced to a specific anatomic area because of this functional organization within the hypothalamus.
Anatomically, this structure can be organized in the sagittal plane into three main regions: the anterior, middle, and posterior. Each main region contains hypothalamic nuclei that serve different physiologic functions. The anterior region contains five nuclei: preoptic, paraventricular, supraoptic, suprachiasmatic, and anterior hypothalamic nucleus. The middle region of the hypothalamus is situated directly above the tuber cinereum and the infundibulum and contains three nuclei: the arcuate nucleus, ventromedial nucleus, and dorsomedial nucleus. The posterior region contains the posterior hypothalamic nucleus and the mammillary nucleus in the mammillary bodies.
Anterior Region
Preoptic nucleus: the primary function is the production and secretion of gonadotropin-releasing hormone (GnRH) for sex hormone regulation. GnRH is released into the tuberoinfundibular tract and is transported through the hypophyseal portal system to the adenohypophysis. This nucleus also participates in initiating non-rapid eye movement sleep via the inhibition of histaminergic neurons in the hypothalamus and cholinergic and noradrenergic neurons in the brainstem. It also is involved in thermoregulation.
Paraventricular nucleus: participates in the production and secretion of several hormones, predominantly oxytocin. It also produces and secretes small amounts of vasopressin, also called antidiuretic hormone (ADH). Another hormone produced is a corticotropin-releasing hormone (CRH), which regulates adrenocorticotropin hormone secretion by the anterior pituitary. It also produces thyroid releasing hormone (TRH), which will control hormonal secretion by the thyroid. This nucleus contains glutamate and AngII-releasing neurons, which induce sympatho-excitatory effects, whereas gamma-aminobutyric acid and nitric oxide-releasing neurons induce sympatho-inhibitory effects. These sympathetic effects, when deregulated, have some influence on heart failure.
Supraoptic nucleus: its secretory functions are similar to the paraventricular nucleus, but its primary function is the production and secretion of vasopressin. This nucleus also produces and secretes oxytocin to a lesser degree than the paraventricular nucleus.
Suprachiasmatic nucleus: this nucleus receives direct input from retinal ganglion cells and synchronized body functions with periods of light and dark to a circadian rhythm. It projects to the pineal gland, which secretes the hormone melatonin, a sleep-inducing hormone.
Anterior hypothalamic nucleus: it controls body temperatures, and its function includes cooling or reducing the body temperature.
Middle Region
Arcuate nucleus: this nucleus releases growth hormone-releasing hormone (GHRH) and produces prolactin-inhibiting hormone (dopamine).
Ventromedial nucleus: this is the center of satiety or fullness.
Dorsomedial nucleus: this is an emotional response center. Stimulation of this nucleus, in animal experiments, produced aggressive behavior that lasts only as long as the stimulus is applied. It is also involved with blood pressure, heart rate, and gastrointestinal stimulation.
Posterior Region
Mammillary nucleus: this nucleus is part of the limbic system, a system that is responsible for memory, behavior, motivation, and motivation. Degeneration of this nucleus classically occurs in Korsakoff syndrome. It is involved in memory, changes in emotion, and heart failure.
Posterior hypothalamic nucleus: this region participates in blood pressure regulation, pupillary dilation, and thermoregulation, particularly body temperature conservation, such as shivering when a person is cold.
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