The hypothalamus is the primary region of integration between the central nervous system (CNS) and the endocrine system, as well as a central structure in the limbic system of the brain in the regulation of autonomic nervous system functions. Input from a vast array of neural, humoral and endocrine sources is processed, coordinated and then relayed into:
- the secretion of factors which stimulate or inhibit anterior pituitary function
- the release of neurohypophyseal hormones
- efferent output to the CNS.
The hypothalamus is a structure which surrounds or lines the 3rd ventricle of the brain immediately superior to the pituitary. It is connected to the pituitary gland by a narrow stalk composed of the unmyelinated axons of neurons which project from the paraventricular nucleus to terminate in the posterior pituitary. There is a network of blood vessels which traverse between the hypothalamus and anterior pituitary.
Hypothalamic neurons can be divided into three categories based on the type of output they use. Magnocellular neurons terminate in the posterior pituitary and secrete into the capillary bed. Parvicellular neurons secrete release/inhibiting hypophyseotrophic factors into the portal system.
The factors and hormones secreted from the hypothalamus and pituitary are secreted in bursts or pulses according to rhythms generated in the hypothalamus or the CNS. Rhythms may be circadian, diurnal, or even ultradian.
Several hypothalamic-pituitary-systemic axes exist, including the hypothalamic-pituitary-thyroid, -adrenal, -gonadal, -prolactin and -growth-hormone axes.
Acquired diseases of the hypothalamic-pituitary system stem from a number of causes, including trauma, tumours, infection, inflammation or poor nutrition. Also, diseases can be secondary to other conditions, such as pregnancy, thyroid disease, diabetes mellitus, or treatment for Cushing's. Interestingly, there are also psychogenic causes, such as the maternal deprivation that can lead to psychosocial dwarfism. Lastly, disease can be inherited, such as with Prader-Willi syndrome, though inherited diseases are less common.
Regardless of the cause, diseases of the hypothalamic-pituitary system may result in failures and abnormalities in neurological development, which leads to disruptions and failures of hypothalamic rhythms.