Pituitary gland

The pituitary gland, or hypophysis, is a pea-sized gland of the endocrine system, situated at the base of the brain. As part of the HPA axis, it is regulated by the hypothalamus to produce, store, and secrete various hormones, which target other endocrine glands. The pituitary gland is sometimes referred to as the “master gland” as it regulates the function of the other endocrine glands.

Structure and Function
The pituitary gland sits at the base of the brain, underneath the hypothalamus. It is surrounded by a protective bony cavity called the sella turcica. The pituitary is divided into three distinct lobes: posterior, anterior, and intermediate.

Posterior
The posterior pituitary develops as an extension of the hypothalamus (distinct from the anterior pituitary). The posterior pituitary is largely made up of the terminals of nerve cells of the hypothalamus, as neurons in the hypothalamus project directly to the posterior pituitary. Hormones produced by the hypothalamus are stored in the terminals of hypothalamic neurons in the posterior pituitary, and are released by nerve excitation. The two major hormones stored and secreted by the posterior pituitary include:
 * Antidiuretic hormone (ADH, also known as vasopressin)
 * Oxytocin

Anterior
The anterior pituitary is structurally distinct from the posterior pituitary. It makes up 80% of the pituitary gland, and is made up of different types of endocrine cells. These cells are classified by the hormones they synthesize and release, and are regulated by the hypothalamus via releasing and inhibiting hormones. The six major hormones of the anterior pituitary are:
 * Growth hormone (GH)
 * Adrenocorticotropic hormone (ACTH)
 * Thyroid-stimulating hormone (TSH)
 * Follicular-stimulating hormone (FSH)
 * Luteinizing hormone (LH)
 * Prolactin

Intermediate
The intermediate lobe is present in many lower vertebrates, but is almost absent in humans. The intermediate pituitary synthesizes and secretes:
 * Melanocyte-stimulating hormone (MSH)

Dysfunction and Disease
Dysfunction of the pituitary gland can result in overproduction or underproduction of pituitary hormones, thus having major consequences in bodily function. Conditions of pituitary malfunction include:
 * Acromegaly -- overproduction of GH
 * Cushing’s disease -- overproduction of ACTH
 * GH deficiency -- underproduction of GH
 * Syndrome of inappropriate antidiuretic hormone -- overproduction of antidiuretic hormone
 * Diabetes insipidus -- underproduction of antidiuretic hormone
 * Sheehan syndrome -- underproduction of any pituitary hormone
 * Pickardt-Falhbusch Syndrome -- underproduction of any pituitary hormone aside from prolactin
 * Hyperpituitarism (usually pituitary adenoma) -- overproduction of any pituitary hormone
 * Hypopituitarism -- underproduction of any pituitary hormone
 * Hypophysitis -- inflammation of the pituitary gland
 * Autoimmune hypophysitis -- inflammation of the pituitary gland due to autoimmunity
 * Pituitary adenoma -- noncancerous tumor of the pituitary gland

ME
Dysfunction of the endocrine system, with a focus on HPA axis hypofunction, has been reported in individuals with ME. . It has been suggested that HPA axis hypofunction in ME is caused by chronic activation of the inflammatory and oxidative and nitrosative stress pathways. However, this area of research continues to lack studies with direct measures of pituitary function.

Some patients report that there seems to be a period of pituitary/HPA axis hyperfunction in the earlier stage of ME, whereas later in disease progression there's a switch to hypofunction. This could perhaps explain some of the wide variation across studies (e.g.,  ).

Patients with ME have also reported other problems with the pituitary, such as Empty Sella Syndrome and pituitary adenoma. These may be of note to guide future research.

Learn more
Khan Academy | The hypothalamus and pituitary gland