Arcuate nucleus of hypothalamus

The arcuate nucleus, located within the hypothalamus, plays a critical role in the neuroendocrine system and is linked to the hypothalamic-hypophyseal portal system. This specialized vascular arrangement comprises a network of capillaries designed to efficiently transport hormones from the hypothalamus to the anterior pituitary gland. The primary purpose of this system is to facilitate the rapid release of various hormones, including both releasing factors, which stimulate hormone production, and inhibitory factors, which suppress hormone production.

The paraventricular, dorsomedial, and arcuate nuclei of the hypothalamus also play a major role in regulating food intake. It contains neurons that produce neuropeptides that signal hunger and satiety, influencing food intake. When activated, the arcuate nucleus can increase appetite while suppressing the desire to eat under other conditions. In addition to its role in appetite regulation, the arcuate nucleus is involved in the secretion of growth hormone (GH). It can release inhibitory factors that modulate GH levels in the bloodstream.

Furthermore, the arcuate nucleus is responsible for the secretion of the thyroid-stimulating hormone (TSH) releasing factor, which stimulates the anterior pituitary gland to release TSH, thereby influencing thyroid function and metabolism.

The arcuate nucleus also releases adrenocorticotropic hormone (ACTH), which targets the adrenal cortex, prompting it to produce cortisol, a crucial steroid hormone involved in stress response and metabolism. This release is mediated not only by the arcuate nucleus but also by the neighboring paraventricular nucleus.

Prolactin, another vital hormone, is regulated by the arcuate nucleus through inhibitory factors such as dopamine secretion. When dopamine levels are insufficient, prolactin secretion increases, which can lead to conditions such as galactorrhea—the production of breast milk unrelated to pregnancy or lactation. Elevated prolactin levels can also result from pathological conditions, such as a tumor in the prolactin-secreting cells of the pituitary gland, known as a prolactinoma or adenoma. The connection between the arcuate nucleus and the portal system is facilitated by the tuberohypophysial tract, which consists of nerve fibers that travel from the arcuate nucleus to the portal capillaries. This tract plays a vital role in ensuring that the hormones produced in the hypothalamus are quickly and efficiently delivered to the anterior pituitary gland for further action.