Sunday, April 22, 2012

Day 22


The pituitary is a pea-sized gland located at the base of the brain in the middle of the head and right below the optic nerves. It serves as the “master gland” that regulates the secretion of the majority of hormones in the body from all of the other glands, such as the thyroid and adrenal glands, as well as the ovary and testicles. The pituitary gland is divided into the anterior and posterior lobes, both of which secrete different hormones that have unique functions in the body. The anterior pituitary secretes prolactin, growth hormone and the gonadotropins, which include luteinizing hormone (LH) and follicle stimulating hormone (FSH), adrenocorticotrophic hormone (ACTH) and thyroid stimulating hormone (TSH). The posterior pituitary makes antidiuretic hormone (ADH) and oxytocin. The secretion of the hormones from the pituitary gland itself is also controlled by hormones coming from part of the brain directly above the pituitary called the hypothalamus. The hypothalamus and the pituitary gland are connected by the pituitary stalk.

Pituitary tumors result from a single cell losing the ability to control its growth. These tumors are almost always benign or non-cancerous. Very rarely can a pituitary tumor become malignant or cancerous. A tumor that is less than 1 cm in size is called a microadenoma, and a tumor that is larger than 1 cm is a macroadenoma.

Microadenomas usually do not cause symptoms related to their size, but macroadenomas can cause headaches as well as visual loss secondary to compression of the optic nerves. In addition, the normal pituitary tissue can be compressed by a macroadenoma, so deficiencies of anterior pituitary hormones can be identified on blood tests and based on symptoms. Pituitary tumors are also categorized according to their ability to make hormones and cause symptoms.

The functional tumors include those that secrete prolactin (prolactinomas), ACTH (Cushing’s disease), growth hormone (acromegaly) and TSH. Tumors that do not secrete functional hormones are called non-functioning pituitary tumors. The most common tumors in adults are prolactinomas followed by non-functioning tumors, ACTH-secreting tumors, GH-secreting tumors and TSH-secreting tumors. In children, the most common tumor is also a prolactin-secreting tumor followed by ACTH-secreting tumors, GH-secreting tumors, non-functioning tumors and TSH-secreting tumors.


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