Pituitary Gland

 

Pituitary gland

PKGhatak, MD

The pituitary gland is a small endocrine gland, located at the base of the skull in the middle fossa and sits in the Sella turcica (Turkish saddle) of the sphenoid bone. The roof of the nose is just below it and is separated by a thin perforated bone partition called cribriform plate, the hypothalamus and optic chiasma are located just above the pituitary gland. The pituitary is positioned in between the eyes when projected on the surface. The pituitary is connected with the hypothalamus by a stalk consisting of nerve fibers and blood vessels, The frontal cortex overhangs in front of the pituitary.

The pituitary gland is two glands in one structure - the anterior pituitary and posterior pituitary. Both parts are endocrine in nature. The posterior pituitary is an extension of the hypothalamus. In between the two pituitaries are cells that form pars intermedia.

Embryology of Pituitary.

The ectoderm cells of the developing roof of the mouth grow upwards in the form of a pouch-Rathke's pouch. The neurons from the floor of the 3^rd ventricle of the brain extend down as an outgrowth to meet Rathke's pouch. These two sources make up the Pituitary gland – the anterior pituitary (adenohypophysis) originates from the cells of the roof of the mouth, the posterior pituitary (neurohypophysis) from the extension of the brain. The line of junction of these two parts contains cells and is known as Pars Intermedia. Pars intermedia is ultimately incorporated in the anterior pituitary and these cells produce MSH - melanocyte stimulating hormone. 

The pituitary gland is the conductor of an endocrine orchestra. The orchestra players are the adrenal glands, thyroid, thymus, pancreas, pineal, and testis/ovaries. The nerve center of this orchestra is the hypothalamus. Hypothalamus with its nerve fibers and the portal circulatory system sends signals to both pituitary glands. Hypothalamus is the headquarters of the autonomic nervous system. Hypothalamus acts as a bridge between the CNS and endocrine systems 

Special Three:

The pituitary, hypothalamus and pineal have a closer relationship. The pineal gland produces melatonin, a hormone and through melatonin, the pineal maintains the circadian cycle, sleep, and waking rhythm. The pineal gland is considered the spiritual center and so called the 3^rd eye. These three structures (Pituitary, hypothalamus and pineal gland) working together are responsible for the control of heart rate, BP, apatite, body temperature, respiration, emotion and behavior, sexuality and fertility, growth, of bones & muscles. skin color, water & electrolyte balance and health.

Hypothalamus communicates with the anterior pituitary by releasing hormones. Every anterior pituitary hormone is produced by a separate cell line; so, the hypothalamus has multiple releasing hormones.              Examples- ACTRH (adrenocorticotropic releasing hormone), TSRH,GHRH, etc. The nerve fibers from the hypothalamus send signals to release preformed hormones - ADH (antidiuretic hormone) and Oxytocin.

The hormone secretion from the pituitary gland is not continuous. Every 2 to 3 hours hormones are released in circulation.

Hormones of Anterior Pituitary:

Anterior pituitary gland hormones are ACTH (adrenocortical stimulating hormone).

 TSH (thyroid stimulating hormones).

 Gonadotropins- LH (luteinizing hormone), FSH (follicle stimulating hormone).

 MSH (Melanocyte stimulating hormone).

Posterior Pituitary hormones are. ADH (antidiuretic hormone) and Oxytocin.

ADH is produced by neurons of the hypothalamus and travels down the nerve fibers to the posterior pituitary and is stored in the vesicles. With the appropriate signal from the hypothalamus, ADH is secreted.

Oxytocin. Oxytocin is likewise produced by neurons of the posterior pituitary, travels to the posterior pituitary like ADH.

The pituitary gland may overproduce or fail to produce adequate quantities of the hormone. It also may develop tumors. Benign tumors of the anterior pituitary are the majority of tumors.

Table of Pituitary hormones.

Hormone	Target organ	Excess production	Deficiency
GH- growth hormone	Bones and muscular system.	Gigantism in children, Acromegaly in adults.	Dwarfism, Growth retardation. Osteoporosis, muscular weakness, depression.
ACTH	Adrenal cortex	Cushing disease	Addison's disease
TSH- thyroid stimulating hormone	Thyroid gland	Hyperthyroidism	Hypothyroidism
Gonadotropin LH- luteinizing hormone	Germ cells of Ovaries/testicles		Failure to conceive if female. Low sperm count in males.
Gonadotropin FSH- follicle stimulating hormone	Interstitial cells of ovaries/testicles	Many adverse effects on estrogen excess and hyper testosterone, Blood clots to increase hepatic and other tumors.	Few and scanty menstruation to amenorrhea in females. Erectile disorder in male.
Prolactin	Breast both sexes	Lactation without pregnancy. Milk secretion in male	Lactation deficiency in post partem..
MSH- melanocyte stimulating hormone	Melanocytes of skin	Production of pigments of skin and hair	Vitiligo and albinism
ADH- antidiuretic hormone	Kidney tubules	Fluid overload and hyponatremia	Dehydration and inappropriate production of dilute urine
Oxytocin	Pregnant Uterus	Rupture uterus	Failure of placental separation and poor uterine contraction during labor.

A few special Pituitary disorders.

Chromophobe Adenomas of Pituitary. Chromophobe adenoma of the pituitary is the most common adenoma and is a benign tumor. Pituitary adenoma does not secrete any hormone. and cells contain no granules, however, under the electron microscope, a few granules are detected. Symptoms of adenoma are related to increased internal pressure and hypofunction of the pituitary but symptoms vary because all different cell lines are not equally affected. Often the prolactin levels are high and ACTH, TSH and GH are lower.

MENS 1. Multiple endocrine neoplasia type one. Tumors of the anterior pituitary (mostly of prolactin producing cells) arise in association with tumors of parathyroid glands, pancreatic tumors – insulinomas and glucagonomas, and tumors of small intestinal hormone producing cells. The disease is inherited in an autosomal dominant pattern. Additional tumors of the adrenal gland, carcinoids, angiofibroma and meningiomas may be associated.

Sheehan syndrome. Massive postpartum bleeding leads to shock and pituitary necrosis. If patients survive the shock, then hypothyroidism, adrenal insufficiency, and menopause develop.

Empty Sella syndrome. The pituitary sits in a bony cup, only the top is covered by soft tissues. In benign intracranial hypertension, the persistent high CSF pressure produces gradual atrophy of the pituitary and symptoms of hypopituitarism develop.

Prolactinoma. Tumors of prolactin producing cells are either microscopic tumors or macroscopic large tumors- both are benign. Excess prolactin is associated with a deficiency of other anterior pituitary hormones. Symptoms of low cortisol and hypothyroidism are most manifested initially. Macrotumors produce increased CSF pressures, visual field defects, and eye muscles palsy in addition to hormonal changes.

Nelson syndrome. Following bilateral adrenal gland removal in Addison syndrome, the cells producing ACTH in the pituitary grow in excess and forms tumor. Besides Cushnoid features, various visual symptoms and blindness may develop.

Craniopharyngioma. Craniopharyngiomas are benign cysts and occasionally solid adenoma developed from the remnant cells of Rathke's pouch. Symptoms are increased intracranial pressure and visual field defects. This entity is a childhood malady and is occasionally seen in adults.

Rathkes cleft cysts. Cysts develop in the remnant Rathkes pouch. The presentation is very similar to craniopharyngioma.

Lymphocytic hypophysitis. This entity is a rare complication seen in late pregnancy or early postpartum. It is an autoimmune disease with lymphocytic infiltration of the pituitary gland and results in various degrees of hypofunction of the pituitary. The cause is unknown, IgG4 and IgG1 antibodies were detected by some investigators pointing to heterogenic sources of antigen.

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