The pituitary gland is a small gland at the base of the brain that produces a large number of the hormones controlling growth, sexual development, and water balance. The gland also produces hormones that control many other hormone-secreting glands, such as the thyroid gland. Most pituitary disorders are caused by tumours that alter the output of particular pituitary hormones.
This section opens with a discussion of various tumours of the pituitary gland. Some types cause underproduction of particular hormones, and others cause overproduction. The abnormal hormone levels can have adverse effects elsewhere in the body; these effects are discussed in the articles that follow.
Particular pituitary hormones affect other hormone-secreting glands in the body; a pituitary disorder may thus lead to a disorder in another gland (see Thyroid and parathyroid gland disorders, and Adrenal gland disorders). Sex hormone disorders that may be caused by a problem with the pituitary gland are discussed elsewhere (see Male hormonal disorders, and Menstrual, menopausal, and hormonal problems), as are growth abnormalities in children that result from pituitary disorders (see Growth disorders).
For further information on the structure and function of the pituitary gland, see Hormones and Metabolism.
The thyroid and parathyroid glands are situated in the neck, where they produce and secrete hormones into the bloodstream. There are two types of thyroid hormone, both of which help to control the rate of metabolism (the chemical reactions constantly occurring in the body). The four small parathyroid glands produce a hormone that controls calcium levels in the blood.
Thyroid disorders are common, but their onset is often gradual and they may not be detected or diagnosed for months or even years. Low levels of thyroid hormones at birth can prevent normal development of the brain and, for this reason, a blood test for thyroid hormone levels is one of the first tests to be performed on a newborn baby (see Blood spot screening tests). Over- and underactivity of the thyroid gland are the most common thyroid disorders and are discussed first. Swellings and growths are covered next, followed by disorders in which there is over- or underproduction of hormones by the parathyroid gland.
The last article describes multiple endocrine neoplasia, a group of rare inherited disorders in which tumours develop in several endocrine glands, including the thyroid and parathyroid.
For further information on the structure and function of the thyroid and parathyroid glands, see Hormones and Metabolism.
There are two adrenal glands, one situated above each kidney. Hormones produced by the adrenal glands are vital in controlling body chemistry. If adrenal hormone levels become imbalanced, the effects tend to be widespread throughout the body and are often serious, even life-threatening. However, these disorders are rare.
Adrenal gland disorders may involve either the over- or underproduction of adrenal hormones. This section first discusses disorders in which adrenal hormones are overproduced. The overproduction of adrenal hormones is most commonly due to the presence of an adrenal tumour. These tumours are usually noncancerous and can often be removed by means of surgery.
The final article discusses Addison’s disease, a disorder in which the adrenal gland underproduces hormones. The lack of adrenal hormones is frequently caused by an autoimmune disorder that damages the gland. Addison’s disease can be treated successfully with synthetic hormones.
Adrenal disorders are sometimes caused by changes in the levels of hormones that are produced by the pituitary gland (see Pituitary gland disorders). There is also an extremely rare adrenal disorder that is caused by a genetic defect (see Congenital adrenal hyperplasia). Disorders that are due to the abnormal production of sex hormones by the adrenal glands are described elsewhere in the guide (see Male hormonal disorders, and Menstrual, menopausal, and hormonal problems).
For more information about the structure and function of the adrenal glands, see Hormones and Metabolism.
The chemical processes that take place in the body are known collectively as metabolism. These processes are largely controlled by hormones, and either overproduction or underproduction of a particular hormone can have wide-ranging effects on the body’s internal chemistry. Metabolic disorders can also be caused by underlying conditions affecting major organs that regulate metabolism, such as the liver and the kidneys.
One important group of metabolic disorders is due to faulty or blocked chemical pathways, which cause the build-up of a chemical that is usually eliminated from the body. As the chemical accumulates, it may damage organs such as the brain and the liver. Many of these disorders, such as haemochromatosis, are due to genetic defects, some of which tend to run in families. If you have a close relative with one of these disorders, you may be at increased risk of developing the metabolic disorder yourself (see Gene disorders).
Most metabolic disorders can be diagnosed using blood or urine tests to measure levels of hormones or other specific chemicals. If the disorders are recognized early, they can sometimes be treated by a change in diet or the replacement of missing hormones or other chemicals. The sooner treatment is started, the better the prospects are for avoiding permanent damage.
The opening article in this section describes diabetes mellitus, the most common metabolic disorder. The next discusses hypoglycaemia, a condition sometimes associated with treatment for diabetes. The final articles cover disorders, including amyloidosis, in which abnormal levels of particular substances collect in the body.
Certain metabolic disorders are also disorders of particular endocrine (hormone-secreting) glands and are described elsewhere (see Pituitary gland disorders; Thyroid and parathyroid gland disorders; and Adrenal gland disorders).
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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