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The endocrine glands, or ductless glands, discharge their secretions (hormones) directly into the blood; they include the adrenal, pituitary, thyroid, and parathyroid glands, the islands of Langerhans in the pancreas, the gonads, the thymus, and the pineal body. The exocrine glands discharge through ducts opening on an external or internal surface of the body; they include the salivary, sebaceous, and sweat glands, the liver, the gastric glands, the pancreas, the intestinal, mammary, and lacrimal glands, and the prostate. The lymph nodes are sometimes called lymph glands but are not glands in the usual sense.
Thyroid crisis is a serious event that can be fatal if not brought under control. All of the body processes are accelerated to dangerously high levels. The pulse may rise to 200 beats per minute, and there is concurrent rise in the respiratory rate. The temperature control center loses control, bringing about a rapid and steady increase in body temperature. Pulmonary edema and congestive heart failure can also occur.
Treatment is aimed at correction of the hyperthyroidism, control of the symptoms, and prevention of further crisis by treating the underlying cause. Medications are employed to block synthesis of thyroid hormones, block their release, and inhibit conversion of triiodothyronine to thyroxine. plasmapheresis. plasma exchange, or hemodialysis may be necessary to remove the hormones from the circulation.
Supportive care includes administration of oxygen and measures to control hyperthermia, such as the use of ice packs or a hyperthermia blanket. Intravenous hydration is important to prevent shock. The use of glucocorticoids is associated with improved survival rates. propranolol, sympatholytics, and guanethidine are often used, as well as other medications that treat symptoms.
Diagnostic tests for thyroid disorders include radioimmunoassay for T3, T4, and thyroid-stimulating hormone (TSH), free thyroxine serum concentration, and free thyroxine index (FTI). These and other thyroid function tests can be distorted by preparations and foods containing iodine, and by oral contraceptives, phenytoin (Dilantin), and several other drugs. The thyroid scan is useful in detecting nodules and active thyroid tissue and, combined with radioactive iodine uptake, measures the ability of the thyroid gland to take in ingested iodine.
Persons who received radiation to the head and neck as children are at higher than normal risk for development of thyroid abnormalities. Of these disorders about one-third are carcinomas of the thyroid. Other problems related to radiation early in life include adenomas and other malignant and benign tumors, hypo- and hyperthyroidism, and thyroiditis. The American Thyroid Association suggests periodic laboratory testing and physical assessment of persons at high risk in order to detect these abnormalities when they are more amenable to treatment.
Secretion of thyroid hormones is regulated by the hypothalamus-pituitary-thyroid control system. Internal environmental conditions, such as low thyroid hormone and norepinephrine serum levels, or external factors, such as cold and stress, activate the hypothalamus, which secretes thyrotropin-releasing hormone (TRH). This hormone acts on the pituitary gland and brings about the release of thyroid-stimulating hormone (TSH). The TSH then stimulates the release of thyroid hormones such as T3 and T4 from the thyroid gland. When sufficient levels of serum thyroxine and other thyroid hormones have been reached, there is negative feedback to the hypothalamus and TRH is no longer secreted. See also hypothyroidism and hyperthyroidism.
thy·roid gland(thī'royd gland) [TA]
thyroid glandAn ENDOCRINE GLAND, situated in the neck like a bow tie across the front of the upper part of the windpipe (trachea). The gland secretes hormones that act directly on almost all the cells in the body to control the rate of their METABOLISM.
thyroid glanda large endocrine organ situated in the region of the neck which produces THYROXINE, a hormone that contains iodine obtained from the diet. Thyroxine controls BASAL METABOLIC RATE (BMR), and also controls metamorphosis in amphibians. Undersecretion during development causes hypothyroidism (reduced physical and mental development) leading to CRETINISM in subadults. In the adult stage MYXOEDEMA results, and this gives rise to general slowness of thought and action, coarse skin and fatness. Overproduction, (hyperthyroidism) causes exophthalmic goitre, where the thyroid, and thus the neck, swells and the eyeballs protrude. Those so affected become restless and overactive, lose weight and have an accelerated heart rate. Deficiency or excess of iodine in the diet causes malfunction of the thyroid gland. A deficiency occurs naturally in, for example, parts of Derbyshire, where the symptoms are known as Derbyshire Neck.
thyroid glandthe gland in the front of the neck which secretes the iodine-containing hormones thyroxine (T4) and triiodothyronine (T3) necessary for normal growth in childhood, and crucial in the control throughout life of energy metabolism. The hormones target most body cells (except in the CNS) where they modify enzyme synthesis, thereby controlling the rate of aerobic metabolism and heat production. Thus overactivity (hyperthyroidism) causes increase in BMR and body temperature with weight loss, and deficiency (hypothyroidism) the reverse. Regulated by thyrotrophic hormone from the anterior pituitary, and in turn by the hypothalamus. Also secretes calcitonin which acts to decrease blood [Ca2+]. See also hormones, parathyroid glands; Table 1.
|Site of production||Name of hormone||Main targets||Involved in regulating:||Secretion controlled by:|
|Hypothalamus||Releasing and inhibiting hormones||Anterior pituitary (via local blood vessels)||Secretion of anterior pituitary hormones||Other brain regions; feedback re regulated hormones and their actions|
|Neurohormones released from posterior pituitary:|
|Oxytocin||Uterus, breasts||Labour and lactation||Afferent information from target organs|
|Antidiuretic hormone (ADH, vasopressin)||Kidneys||Water loss: ECF volume and osmolality||Hypothalamic osmoreceptors|
|Anterior pituitary||(Human) growth hormone (H)GH||Most cells||Growth and metabolism||Hypothalamic releasing and inhibiting hormones via local blood vessels|
|Thyroid-stimulating (TSH)||Thyroid gland||Thyroid secretions|
|Gonadotrophins||Ovary or testis||Germ cell maturation and hormone secretions|
|Adrenocorticotrophic (ACTH)||Adrenal cortex||Cortisol secretion|
|Pineal body||Melatonin||Widespread, including brain, thymus, etc.||Hypothalamus; varying light input from retina|
|Parathyroids||Parathormone||Bone, kidneys, gut||ECF [Ca2+]|
|Medulla||Heart, smooth muscle, glands||Cardiovascular and metabolic adjustments to activity and stress||Sympathetic nervous system|
|Atrial wall||Atrial natriuretic hormone||Kidneys||Blood volume; increases sodium (therefore also water) loss in urine||Stretch of atrial wall by venous pressure|
|Gonads: Testis||Androgens (mainly testosterone)||Genitalia and other tissues||Reproductive function and sex characteristics||Anterior pituitary gonadotrophins|
|Ovary||Uterus, breasts and other tissues||Menstrual cycle, pregnancy, lactation|
|Pancreas||Blood levels, storage and cellular uptake of nutrients, notably glucose, but also proteins and fats||Blood levels of nutrients; autonomic nervous system; other gastrointesinal hormones|
|Stomach||Gastrin||Gastric acid-secreting cells||Gastrointestinal functions: motility, digestive juices and other secretions||Local chemical and mechanical factors in the alimentary tract|
|Small intestine||Several GI functions including bile flow, pancreatic enzyme and exocrine secretions||Ingestion of food, distension of GI tract|
thy·roid gland(thī'royd gland) [TA]
Patient discussion about thyroid gland
Q. Anyone know if there is a connection between Fibromyalgia and your Thyroid gland? I have Fibromyalgia and I read that if your diagnosed with this you can have Thyroid problems also. If anyone knows out there please inform me. Many thanks.
Q. Is there any natural herb for a sluggish thyroid My uncle is suffering with thyroid for the past 8 months and the treatment he underwent is not successful. Is there any natural herb for a sluggish thyroid?
Q. I was told to have my thyroid test and now after the result they have told me to go for MRI I am 23 years old lady……I was told to have my thyroid test and now after the result they have told me to go for MRI……..and I know one of my friend had same type of symptoms and after thyroid test she was on her medicines and now she is well…they say it may be fibromyalgia or sclerosis …why they want me to go for MRI…..there seems to be something serious?