The Pituitary gland is a small structure, the size of a pea, located in the under surface of the brain. A pituitary gland is essential for a person to live. It controls the function of most endocrine glands (hormone producing glands) in the body.
The Pituitary gland controls the function of other endocrine glands by secreting several important hormones including:
1. TSH (thyroid stimulating hormone)
2. ACTH (adrenocorticotropic hormone)
3. FSH (Follicle stimulating hormone)
4. LH (luteinizing hormone)
5. GH (Growth hormone)
7. ADH (antidiuretic hormone)
These pituitary hormones, in turn, control the function of several endocrine organs (the target organs) in the body.
TSH regulates the production of Thyroid hormones (T4 and T3) by the thyroid gland.
ACTH regulates the production of Adrenal hormones (cortisol and sex hormones) by the adrenal glands.
LH and FSH regulate the production of Sex hormones and eggs by the ovaries in women and Sex hormones and sperm by the testes in men.
GH regulates growth during childhood and puberty and continues to regulate the health of bones and muscles in adults.
Prolactin regulates Lactation in women.
ADH regulates the urine concentrating ability of the kidneys.
The target organ hormones control the production of pituitary hormones through a negative feedback mechanism. For example, if thyroid hormones (T4 and T3) are low, the pituitary gland produces a large amount of TSH, whereas production of TSH is diminished in response to a high level of thyroid hormones (T4 and T3).
Pituitary hormone production is also controlled by a higher center in the brain called the hypothalamus, which in turn is influenced by the other areas in the brain, especially the limbic system, which is involved in regulating the emotions of a person. This explains how the emotional state of a person can influence the function of the endocrine organs. For example, women experiencing severe emotional trauma often stop having their menses.
Pituitary tumors are benign in most patients, but rarely may be cancerous. When cancerous, it is usually the manifestation of a metastases from a distant site such as the lung, colon, breast, etc.
Pituitary tumors are often discovered incidentally on a brain CT or MRI scan.
Pituitary tumors may be hormone producing tumors or non-hormone producing.
Pituitary tumors may cause symptoms through one of the following mechanisms:
1. Due to pressure of the pituitary tumor on the surrounding
structures in the brain.
Pressure of the pituitary tumor onthe surrounding brain structures can give rise to defects in the visual field, double vision and severe headaches.
2. Due to overproduction of hormones by the pituitary tumor.
Prolactin producing tumors are the most common type of pituitary tumors. High prolactin level in women can give rise to milk production, menstrual irregularities or infertility. High prolactin level in men can decrease testosterone level which in turn causes a decrease in libido, impotence and muscle weakness. High prolactin level is not always due to a pituitary tumor and can result from certain drugs, hypothyroidism, renal failure, breast manipulation, food, stress, etc.
Growth hormone producing tumors are rare and can give rise to a disease state, known as Acromegaly.
ACTH (adrenocorticotropic hormone) producing tumors are rare and may give rise to a disease state, known as Cushing's syndrome.
TSH producing tumors are even rarer and can give rise to hyperthyroidism (overactive thyroid).
LH and FSH producing tumors are rare and can give rise to sexual symptoms in men as well as women.
3. Due to underproduction of pituitary hormones as a result of local pressure effect of the tumor on the pituitary gland.
This may cause fatigue and lack of a sense of well being due to low thyroid hormones, low cortisol, low growth hormone and in men, low testosterone level as well.
Underproduction of pituitary hormones is known as hypopituitarism, which can result from the pressure effect of the pituitary tumor on the pituitary gland or due to surgery and/or radiation therapy of a pituitary tumor.
Hypopituitarism usually manifests as fatigue and muscle weakness due to deficiency of several target organ hormones such as thyroid hormones, cortisol, growth hormone and testosterone.
Management of Pituitary tumors
Management of pituitary hormones is complex and must be carried out in consultation with an endocrinologist.
Evaluation of a pituitary tumor includes:
Is the pituitary tumor producing a hormone or not?
Is the pituitary tumor causing any pressure effects on the surrounding brain structures?
Is there evidence of hypopituitarism?
Prolactin producing tumors are effectively treated with medications. Surgery is only rarely indicated.
Other pituitary tumors generally require surgery and at times, radiation therapy as well.
Hypopituitarism is treated effectively by replacing the deficient hormones.
This article was written by Sarfraz Zaidi, MD, FACE. Dr. Zaidi specializes in Diabetes, Endocrinology and Metabolism.
Dr. Zaidi is a former assistant Clinical Professor of Medicine at UCLA and Director of the Jamila Diabetes and Endocrine Medical Center in Thousand Oaks, California.
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