the growth years an overproduction of somatotropin causes giantism while the lack of it causes dwarfism. An overproduction after the growth years causes acromegaly, which is characterized by the development of abnormally large hands, feet, and jaw.
THYROTROPIN, or the thyroid-stimulating hormone (TSH), influences the growth, development, and secreting activities of the thyroid gland.
GONADOTROPIN influences the gonads (ovaries or testes) and is essential for the normal development and functioning of both male and female reproductive systems.
The ADRENOCORTICOTROPIC hormone (ACTH) acts primarily on the adrenal cortex, stimulating its growth and its secretion of corticosteroids. Removal of the pituitary leads to rapid atrophy of the adrenal cortex.
The posterior lobe of the pituitary produces at least two hormones, vasopressin and oxytocin. VASOPRESSIN acts as an antidiuretic hormone (ADH), promoting the conservation of water by the kidney. When ADH is not produced in adequate amounts, the daily urine volume is between 10 and 15 liters instead of the normal 1.5 liters. This condition is known as diabetes insipidus.
OXYTOCIN stimulates contraction of the muscles of the uterus, particularly during pregnancy. It also plays an important role in the production of milk in the mammary glands of nursing mothers.
THYROID GLAND
The thyroid, shaped like a butterfly, lies in the anterior part of the neck, below the larynx. It consists of two lobes, one on each side of the upper trachea, connected by a strip of tissue called the isthmus. The thyroid secretes the iodinecontaining hormone THYROXIN, which controls the rate of cell metabolism. Excessive secretion of thyroxin raises the metabolic rate and causes hyperthyroidism, a condition characterized by a fast pulse rate, dizziness, increased basal metabolism, profuse sweating, tremors, nervousness, and a tremendous appetite yet a loss of weight. The thyroid may become enlarged.
Iodine is essential for the formation of thyroxin. To prevent simple goiter, iodine-containing foods, such as vegetables, iodized salt, and seafood, are eaten.
Hypothyroidism, on the other hand, is caused by an insufficient secretion of thyroxin. The patient exhibits a decrease in basal metabolism, and sweating is almost absent. There may be a weight gain and constant fatigue. The heart rate may be slow, and there may be an enlargement of the gland, called a simple goiter. There may also be personality changes characterized by slow, lethargic mental functioning. Hypothyroidism in an infant may result in cretinism with impaired mental and physical development.
PARATHYROID GLANDS
Parathyroid glands are four small round bodies located just posterior to the thyroid gland. Their hormone, PARATHORMONE, regulates the calcium and phosphorus content of the blood and bones. The amount of calcium is important in certain tissue activities, such as bone formation, coagulation of blood, maintenance of normal muscular excitability, and milk production in the nursing mother. Diminished function or removal of the parathyroid glands results in a low calcium level in the blood, and in extreme cases death may occur, preceded by strong contraction of the muscles (tetany) and convulsions.
Hyperparathyroidism, an excess of parathyroid hormone in the blood, causes calcium levels in the blood to become elevated by the withdrawal of calcium from the bones, leaving the skeleton demineralized and subject to spontaneous fractures. The excess calcium may be deposited as stones in the kidneys.
ADRENAL GLANDS
The adrenal glands are located on the superior surface of each kidney, fitting like a cap. They consist of an outer portion, the cortex, and an inner portion, the medulla.
Adrenal Cortex
Specialized cells in the outer layer of the adrenal cortex produce three types of steroid hormones that are of vital importance.
MINERALOCORTICOIDS are regulators of fluid and electrolyte balance. They are sometimes called salt and water hormone because they regulate the excretion and absorption of sodium, chlorine, potassium, and water.
GLUCOCORTICOIDS are essential to metabolism. They increase certain liver functions and have an anti-inflammatory effect. Clinically they are used to suppress inflammatory reactions, to promote healing, and to treat rheumatoid arthritis.