The Human Pituitary Gland
The pituitary gland lies in a bony hollow at the base of the brain. It is approximately 15 mm long and 5 mm across. It is attached to the brain by a stalk or nerve fibers, which is continuous with the hypothalamus above, behind the optic chiasm.
The pituitary gland is a small gland, located below the brain and connected to the hypothalamus. The pituitary gland regulates the secretions of hormones in the body, and hormones impact metabolism, growth and development, reproduction and urine production. It is important to note that the hypothalamus and pituitary gland are connected by blood vessels and nerves.
When the body experiences changes, perhaps in temperature, the hypothalamus responds to restore our body’s balance (homeostasis). The hypothalamus stimulates the pituitary gland to release hormones that in term stimulate various organs in the body to respond. The pituitary gland has cells that respond independently to the stimulus. Some cells make one type of hormone, other cells produce other hormones. The pituitary gland is often referred to as the master gland.
The pituitary gland is reddish-gray in color and roughly oval in shape. It is regarded as the master gland of the body, since through its hormones it controls the activities of many of the other endocrine organs. Basically, it consists of two distinct parts- the anterior and posterior lobes, which have several modes of development and entirely different functions.
The Anterior lobe
This part of the pituitary gland is the larger one and produces a number of hormones which controls the production of the secretions of all the other endocrine organs.
- The Growth hormone or Somatotrophic hormone (GH):
This hormone promotes protein anabolism, absorption of calcium and conversion of glycogen to glucose, thus influencing growth and so regulates growth in height.
Over secretion of this hormone in childhood leads to excessive growth called as gigantism and under secretion results dwarfism. In adults, over activity results in acromegaly where the hands, feet and face enlarge progressively.
Secretions of the hormone are controlled by the hypothalamus.
- Thyrotrophic Hormone (TSH):
This hormone controls the growth and activity of the thyroid gland. It influences the uptake of iodine, synthesis of the hormone, thyroxin, by the thyroid gland and the release of stored hormones into the blood stream.
- Adrenocorticotrophic hormone (ACTH):
This hormone stimulates the cortex of the adrenal gland to secrete its own hormone.
- Lactogenic hormone (Prolactin):
This hormone helps to control the secretion of milk from the breast.
- Gonadotrophic hormones:
These hormones are essential for normal development of the sex organs and stimulate the production of various sex gland hormones. They are:
- The follicle-stimulating hormone (FSH): In the female, this stimulates the ovarian follicles to produce Estrogen. In the male it stimulates the production of spermatozoa in the testes.
- The Luteinizing hormone (LH): In the female, this stimulates the corpus-luteum of the ovary to produce progesterone and in the male it stimulates the testes to produce testosterone.
The posterior lobe of the pituitary gland is composed of secretary cells which produces two hormones:
- Anti diuretic hormone (ADH) or Vasopressin: It helps to regulate the output of water from the kidney by increasing the absorption of water in the distal renal tubules and collecting ducts. It also raises blood pressure, by contracting the in-voluntary muscles of the intestine and bladder.
- Oxytocin: This stimulates the plain muscles of the uterus during and immediately after labor. It also stimulates the lactating breast to reject milk.
Symptoms of a Pituitary Tumor
This depends on the type of tumor and the size of the tumor. A large tumor may cause loss of vision, particularly peripheral vision, if it compresses the optic chiasm (where the optic [eye] nerves converge). Headache may also occur; the type of headache varies from patient to patient. Headache may occur with a large or a small tumor. A tumor may interfere with normal pituitary function causing hypothyroidism (low thyroid hormone level), adrenal insufficiency (low cortisol level), hypogonadism (loss of sexual function in men, loss of menstrual periods or infertility in women). Occasionally a pituitary tumor causes diabetes insipidus, which results in frequent urination and excessive thirst. Diabetes insipidus is not high blood sugar levels; it is a problem with the ability of the kidney to retain fluid because of a deficiency of the pituitary hormone, vasopressin (also called antidieuretic hormone).
Specific types of tumors cause various symptoms and changes in body function.
- Prolactinoma: most commonly causes loss of sexual function and infertility in men. Men may also have enlargement of the breasts. In women of reproductive age a prolactin producing tumor may cause milk in the breasts, a change in menstrual periods or loss of menses or infertility. Women who have gone through menopause do not have a change in menstrual periods to signal the problem; in this situation, headache and loss of vision may be the first indicator of a prolactinoma.
- Cushing's: The term "Cushing's Disease" refers to the overproduction of cortisol by the adrenal glands caused by a pituitary tumor producing an excessive amount of the hormone, ACTH. Dr. Harvey Cushing, a neurosurgeon, first described this condition. Excessive cortisol production causes weight gain (particularly in the abdomen and neck), loss of muscle mass (legs, arms) and muscle weakness, depression, thinning of the skin with easy bruising, hypertension, diabetes mellitus, loss of calcium from the bones (osteoporosis) with a risk for bone fractures and weakening of the immune system with a higher risk of developing infections.
- TSH Secreting Tumor: This is the least common type of hormone-producing pituitary tumor. Excessive TSH stimulates the thyroid gland to produce an excessive amount of thyroid hormone (hyperthyroidism). Symptoms of hyperthyroidism include weight loss, nervousness, rapid heart beat, difficulty sleeping, frequent bowel movements and in women, scant menstrual periods.
- Non Secretory Tumor: This refers to a tumor that does not produce an excessive amount of a pituitary hormone. This type of tumor most commonly causes sexual dysfunction in men and loss of regular menses in premenopausal women. This type of tumor is usually detected after it has become a large tumor causing loss of vision and/or headache and/or hypothyroidism or adrenal insufficiency.
- Craniopharyngioma/Rathke's Cleft Cyst: These tumors are congenital - a defect in the development of the pituitary gland which is present at birth but may not cause a problem until adulthood. This is not a malignant (cancerous) tumor but it may interfere with normal pituitary function causing hypopituitarism. These tumors may also cause diabetes insipidus, frequent urination and excessive thirst.
- Pituitary Cyst: Any endocrine gland may develop a cyst. This occurs commonly in the ovaries and thyroid gland; cysts are benign but cause problems because of enlargement causing headache and interference with normal pituitary function. Most common symptoms are headache and, if the cyst is large, loss of vision and loss of normal pituitary function.
The answer to this question about pituitary tumors was developed by Mary Lee Vance, M.D., Professor of Medicine and Neurosurgery at the University of Virginia. Dr. Vance is an endocrinologist specializing in the treatment of pituitary diseases.
For more information from Dr Vance, see Pituitary Tumors Frequently Asked Questions