Pituitary gland

The pituitary gland, or hypophysis, is an endocrine gland about the size of a pea that sits in a small, bony cavity (sella turcica) covered by a dural fold (diaphragma sellae) at the base of the brain. The pituitary fossa, in which the pituitary gland sits, is situated in the sphenoid bone in the middle cranial fossa at the base of the brain.

The pituitary gland secretes hormones regulating homeostasis, including trophic hormones that stimulate other endocrine glands. It is functionally connected to the hypothalamus by the median eminence.

The hypophysis is also the top cell of the suspensor in a dicot embryo, which will differentiate to form part of the root cap.

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Sections

Located at the base of the brain, the pituitary is functionally linked to the hypothalamus. It is composed of two lobes: the adenohypophysis and neurohypophysis. The adenohypophysis, also referred to as the anterior pituitary is divided into anatomical regions known as the pars tuberalis and pars distalis. The neurohypophysis, also referred to as the posterior pituitary. The pituitary is functionally linked to the hypothalamus by the pituitary stalk, whereby hypothalamic releasing factors are released and in turn stimulate the release of pituitary hormones.

Anterior pituitary (Adenohypophysis)

Main article: Anterior pituitary

The anterior lobe is derived from the oral ectoderm and is composed of glandular epithelium. The anterior pituitary is functionally linked to the hypothalamus via the hypophysial-portal vascular connection in the pituitary stalk. Through this vascular connection the hypothalamus integrates stimulatory and inhibitory central and peripheral signals to the five phenotypically distinct pituitary cell types.

The anterior pituitary synthesizes and secretes important endocrine hormones, such as ACTH, TSH, prolactin, growth hormone, endorphins, FSH, and LH. These hormones are released from the anterior pituitary under the influence of hypothalamic hormones. The hypothalamic hormones travel to the anterior lobe by way of a special capillary system, called the hypothalamic-hypophyseal portal system.

Posterior pituitary (Neurohypophysis)

Main article: Posterior pituitary

The posterior lobe is connected to the hypothalamus via the infundibulum or pituitary stalk, giving rise to the tuberoinfundibular pathway. Hormones are made in nerve cell bodies positioned in the hypothalamus, and these hormones are then transported down the nerve cell's axons to the posterior pituitary.

The hormones secreted by the posterior pituitary are

• Oxytocin, where the majority is released from the paraventricular nucleus in the Hypothalamus
• Antidiuretic hormone (ADH, also known as vasopressin and AVP, arginine vasopressin), the majority of which is released from the supraoptic nucleus in the Hypothalamus

Oxytocin is the only pituitary hormone to create a positive feedback loop. For example, uterine contractions stimulate the release of oxytocin from the posterior pituitary, which in turn increases uterine contractions. This positive feedback loop continues until the baby is born.

Intermediate lobe

There is also a intermediate lobe in many animals. For instance in fish it is believed to control physiological colour change. In adult humans it is just a thin layer of cells between the anterior and posterior pituitary. The intermediate lobe produces melanocyte-stimulating hormone (MSH), although this function is often (imprecisely) attributed to the anterior pituitary.

Functions

The pituitary hormones help control some of the following body processes:

• Growth
• Blood pressure
• Some aspects of pregnancy and childbirth including stimulation of uterine contractions during childbirth
• Breast milk production
• Sex organ functions in both women and men
• Thyroid gland function
• The conversion of food into energy (metabolism)
• Water and osmolarity regulation in the body.

Pathology

Disorders involving the pituitary gland include:

Additional images

See also

• Head and neck anatomy

References

1. ^ Gibo H, Hokama M, Kyoshima K, Kobayashi S (1993). "[Arteries to the pituitary]". Nippon Rinsho 51 (10): 2550-4. PMID 8254920.