The pituitary gland, also called the hypophysis, is an endocrine organ found within a small, bony cavity at the base of the brain. Its primary function is to secrete hormones that regulate homeostasis.
More specifically, the pituitary gland is a glandular structure about the size of a pea. It is located below the brain and above the nasal cavity in a protected pocket called the sella turcica, which is within the sphenoid bone. It connects to the hypothalamus via a neck-like structure called the infundibular stalk. The pituitary gland is divided into three major regions: the anterior lobe (pars distalis), or the adenohypophysis; the median pituitary (pars intermedia); and the posterior lobe (pars nervosa), or the neurohypophysis.
The anterior lobe is derived from epithelial tissue and is intertwined with blood vessels. It accounts for approximately three-fourths of the total weight of the pituitary gland. It secretes and synthesizes major hormones: somatotropin or Growth Hormone (GH), which stimulates bone and tissue growth; thyrotropin or Thyroid-Stimulating Hormone (TSH), which stimulates the growth and function of the thyroid gland; Adrenocorticotropic Hormone (ACTH), which stimulates the growth and function of the adrenal glands; Beta-endorphin, which is a neurotransmitter that dulls pain; Gonadotropins such as Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH), which influence development of the reproductive organs; and prolactin (PRL), which stimulates breast development and maintains milk production. The anterior lobe is controlled by the hypothalamus, which secretes releasing hormones and inhibitory hormones into the capillaries of the Hypophyseal Portal System to signal the anterior pituitary to release certain hormones.
The median pituitary is the avascular zone of the gland, and is composed of basophils, chromophobes, and colloid-filled cysts. Its primary function during fetal development is to produce Melanocyte Stimulating Hormone, which gives pigment to the skin; in adulthood, this region of the pituitary gland is very small or completely absent.
The posterior lobe of the pituitary gland is derived from neural tissue and specialized cells called pituicytes, and is considered an extension of the hypothalamus. The magnocellular neurosecretory cells of the posterior lobe allow nerve axons to project down from the infundibulum through to the pituitary. The posterior lobe secretes two major hormones: vasopressin, which stimulates the reabsorption of water by the kidneys and increases blood pressure by means of vasoconstriction; and oxytocin, which stimulates the uterus during childbirth. However, the hypothalamus synthesizes these hormones. The nervous system sends signals to the neurohypophysis so that it can release hormones, which are then picked up by the blood stream and transported to the target organs.
When a patient presents with decreased secretion of one or more of the eight hormones normally produced by the pituitary gland, they are diagnosed with hypopituitarism. If most or all of the hormones are under-secreted, the patient is diagnosed with panhypopituitarism. Other diseases of the pituitary gland include pituitary tumors and pituitary adenomas.
Image Caption: Pituitary gland. Wikipedia