Thyroxine Health Dictionary

A rare disease that accounts for around 1 per cent of all cancers, cancer of the THYROID GLAND usually presents as an isolated hard nodule in the neck. The rate at which the nodule grows depends upon the patient’s age and type of cancer cell. Pain is not usually a feature, but the increasing size may result in the tumour pressing on vital structures in the neck – for example, the nerves controlling the LARYNX (resulting in hoarseness) and the PHARYNX (causing di?culty in swallowing). If more than one nodule is present, they are likely to be benign, not malignant. Treatment is by surgical removal after which the patient will need to take THYROXINE for the rest of his or her life. Radioactive iodine is usually given after surgery to destroy any residual cancerous cells. If treated early, the outlook is good.... thyroid cancer

The iodine-containing protein that is stored in the thyroid gland. It is converted into circulating thyroxines when the thyroid is stimulated by TSH (Thyroid Stimulating Hormone) from the pituitary (in turn stimulated by the hypothalamus, where thyroxine levels are actually monitored). See: T4... thyroglobulin

A highly vascular organ situated in front of the neck. It consists of a narrow isthmus crossing the windpipe close to its upper end, and joining together two lateral lobes which run upwards, one on each side of the LARYNX. The gland is therefore shaped somewhat like a horseshoe, each lateral lobe being about 5 cm (2 inches) long and the isthmus about 12 mm (••• inch) wide, and it is ?rmly bound to the larynx. The weight of the thyroid gland is about 28·5 grams (1 ounce), but it is larger in females than in males and in some women increases in size during MENSTRUATION. It often reaches an enormous size in the condition known as GOITRE (see also THYROID GLAND, DISEASES OF).

Function The chief function of the thyroid gland is to produce a hormone (see HORMONES) rich in iodine – THYROXINE, which controls the rate of body METABOLISM. Thus, if it is de?cient in infants they fail to grow and suffer LEARNING DISABILITY, a condition formerly known as CRETINISM. If the de?ciency develops in adult life, the individual becomes obese, lethargic, and develops a coarse skin, a condition known as hypothyroidism (see under THYROID GLAND, DISEASES OF). Overactivity of the thyroid, or hyperthyroidism, results in loss of weight, rapid heart action, anxiety, overactivity and increased appetite. (See THYROID GLAND, DISEASES OF – Thyrotoxicosis.)

The production of the thyroid hormone is controlled by a hormone of the PITUITARY GLAND – the thyrotrophic hormone.... thyroid gland

The underproduction of thyroid hormones by an underactive thyroid gland. Most cases are caused by an autoimmune disorder such as Hashimoto’s thyroiditis. More rarely, hypothyroidism results from the removal of part of the thyroid gland to treat hyperthyroidism.

Symptoms include tiredness and lethargy. There may also be muscle weakness, cramps, a slow heart-rate, dry skin, hair loss, a deep and husky voice, and weight gain. A syndrome called myxoedema, in which the skin and other tissues thicken, may develop. Enlargement of the thyroid gland may also occur (see goitre). If the condition occurs in childhood, it may retard growth and normal development.

The disorder is diagnosed by measuring the level of thyroid hormones in the blood.

Treatment consists of replacement therapy with the thyroid hormone thyroxine; usually for life.... hypothyroidism

Celery (Apium graveolens variety dulce).

Plant Part Used: Stalk, leaves, roots, seeds.

Dominican Medicinal Uses: The stalks and leaves are traditionally eaten raw or taken as a juice for treating obesity, high blood pressure, high cholesterol, diabetes and menopausal hot flashes.

Safety: The stalks, leaf and root are widely consumed and generally considered safe. Cases of allergic reaction to the root have been reported. Plants infected with pink rot fungus can cause phototoxicoses.

Contraindications: Internal use of the seeds and essential oil are contraindicated during pregnancy (emmenagoge, abortifacient, uterine stimulating effects) and patients with renal disorders (potential kidney-irritating effect of oil).

Drug Interactions: Celery seeds and seed extract: anticoagulants, warfarin (risk of bleeding, drug potentiation); thyroxine (lowered T4 levels).

Laboratory & Preclinical Data: In vivo: anti-hyperlipidemic, anti-inflammatory, antinociceptive (plant extract); hepatoprotective (seeds).

In vitro: antimicrobial, antioxidant (plant extract); cercaricidal (essential oil); vasodilation (chemical constituent).

* See entry for Apio in “Part 3: Dominican Medicinal Plant Profiles” of this book for more information, including references.... apio

Dwar?sm, or short stature, refers to underdevelopment of the body. The condition, which has various causes, is not common. All children who by the age of ?ve years are at least what is technically known as ‘three standard deviations below the mean’ – well below average size for children of that age – should be referred for specialist advice. Among the causes are:

•genetic: familial; abnormalities of chromosomes, for example, TURNER’S SYNDROME; abnormal skeletal development; and failure of primary growth.

intrauterine growth retardation: maternal disorders; placental abnormalities; multiple fetuses.

constitutional delay in normal growth.

systemic conditions: nutritional de?ciencies; gastrointestinal absorption disorders; certain chronic diseases; psychosocial deprivation; endocrine malfunctions, including HYPOTHYROIDISM, CUSHING’S SYNDROME, RICKETS, dysfunction of the PITUITARY GLAND which produces growth hormone, the endocrine growth controller. Treatment of short stature is, where possible,

to remedy the cause: for example, children with hypothyroidism can be given THYROXINE. Children who are not growing properly should be referred for expert advice to determine the diagnosis and obtain appropriate curative or supportive treatments.... dwarfism

Organs whose function it is to secrete into the blood or lymph, substances known as HORMONES. These play an important part in general changes to or the activities of other organs at a distance. Various diseases arise as the result of defects or excess in the internal secretions of the di?erent glands. The chief endocrine glands are:

Adrenal glands These two glands, also known as suprarenal glands, lie immediately above the kidneys. The central or medullary portion of the glands forms the secretions known as ADRENALINE (or epinephrine) and NORADRENALINE. Adrenaline acts upon structures innervated by sympathetic nerves. Brie?y, the blood vessels of the skin and of the abdominal viscera (except the intestines) are constricted, and at the same time the arteries of the muscles and the coronary arteries are dilated; systolic blood pressure rises; blood sugar increases; the metabolic rate rises; muscle fatigue is diminished. The super?cial or cortical part of the glands produces steroid-based substances such as aldosterone, cortisone, hydrocortisone, and deoxycortone acetate, for the maintenance of life. It is the absence of these substances, due to atrophy or destruction of the suprarenal cortex, that is responsible for the condition known as ADDISON’S DISEASE. (See CORTICOSTEROIDS.)

Ovaries and testicles The ovary (see OVARIES) secretes at least two hormones – known, respectively, as oestradiol (follicular hormone) and progesterone (corpus luteum hormone). Oestradiol develops (under the stimulus of the anterior pituitary lobe – see PITUITARY GLAND below, and under separate entry) each time an ovum in the ovary becomes mature, and causes extensive proliferation of the ENDOMETRIUM lining the UTERUS, a stage ending with shedding of the ovum about 14 days before the onset of MENSTRUATION. The corpus luteum, which then forms, secretes both progesterone and oestradiol. Progesterone brings about great activity of the glands in the endometrium. The uterus is now ready to receive the ovum if it is fertilised. If fertilisation does not occur, the corpus luteum degenerates, the hormones cease acting, and menstruation takes place.

The hormone secreted by the testicles (see TESTICLE) is known as TESTOSTERONE. It is responsible for the growth of the male secondary sex characteristics.

Pancreas This gland is situated in the upper part of the abdomen and, in addition to the digestive enzymes, it produces INSULIN within specialised cells (islets of Langerhans). This controls carbohydrate metabolism; faulty or absent insulin production causes DIABETES MELLITUS.

Parathyroid glands These are four minute glands lying at the side of, or behind, the thyroid (see below). They have a certain e?ect in controlling the absorption of calcium salts by the bones and other tissues. When their secretion is defective, TETANY occurs.

Pituitary gland This gland is attached to the base of the brain and rests in a hollow on the base of the skull. It is the most important of all endocrine glands and consists of two embryologically and functionally distinct lobes.

The function of the anterior lobe depends on the secretion by the HYPOTHALAMUS of certain ‘neuro-hormones’ which control the secretion of the pituitary trophic hormones. The hypothalamic centres involved in the control of speci?c pituitary hormones appear to be anatomically separate. Through the pituitary trophic hormones the activity of the thyroid, adrenal cortex and the sex glands is controlled. The anterior pituitary and the target glands are linked through a feedback control cycle. The liberation of trophic hormones is inhibited by a rising concentration of the circulating hormone of the target gland, and stimulated by a fall in its concentration. Six trophic (polypeptide) hormones are formed by the anterior pituitary. Growth hormone (GH) and prolactin are simple proteins formed in the acidophil cells. Follicle-stimulating hormone (FSH), luteinising hormone (LH) and thyroid-stimulating hormone (TSH) are glycoproteins formed in the basophil cells. Adrenocorticotrophic hormone (ACTH), although a polypeptide, is derived from basophil cells.

The posterior pituitary lobe, or neurohypophysis, is closely connected with the hypothalamus by the hypothalamic-hypophyseal tracts. It is concerned with the production or storage of OXYTOCIN and vasopressin (the antidiuretic hormone).

PITUITARY HORMONES Growth hormone, gonadotrophic hormone, adrenocorticotrophic hormone and thyrotrophic hormones can be assayed in blood or urine by radio-immunoassay techniques. Growth hormone extracted from human pituitary glands obtained at autopsy was available for clinical use until 1985, when it was withdrawn as it is believed to carry the virus responsible for CREUTZFELDT-JAKOB DISEASE (COD). However, growth hormone produced by DNA recombinant techniques is now available as somatropin. Synthetic growth hormone is used to treat de?ciency of the natural hormone in children and adults, TURNER’S SYNDROME and chronic renal insu?ciency in children.

Human pituitary gonadotrophins are readily obtained from post-menopausal urine. Commercial extracts from this source are available and are e?ective for treatment of infertility due to gonadotrophin insu?ciency.

The adrenocorticotrophic hormone is extracted from animal pituitary glands and has been available therapeutically for many years. It is used as a test of adrenal function, and, under certain circumstances, in conditions for which corticosteroid therapy is indicated (see CORTICOSTEROIDS). The pharmacologically active polypeptide of ACTH has been synthesised and is called tetracosactrin. Thyrotrophic hormone is also available but it has no therapeutic application.

HYPOTHALAMIC RELEASING HORMONES which affect the release of each of the six anterior pituitary hormones have been identi?ed. Their blood levels are only one-thousandth of those of the pituitary trophic hormones. The release of thyrotrophin, adrenocorticotrophin, growth hormone, follicle-stimulating hormone and luteinising hormone is stimulated, while release of prolactin is inhibited. The structure of the releasing hormones for TSH, FSH-LH, GH and, most recently, ACTH is known and they have all been synthesised. Thyrotrophin-releasing hormone (TRH) is used as a diagnostic test of thyroid function but it has no therapeutic application. FSH-LH-releasing hormone provides a useful diagnostic test of gonadotrophin reserve in patients with pituitary disease, and is now used in the treatment of infertility and AMENORRHOEA in patients with functional hypothalamic disturbance. As this is the most common variety of secondary amenorrhoea, the potential use is great. Most cases of congenital de?ciency of GH, FSH, LH and ACTH are due to defects in the hypothalamic production of releasing hormone and are not a primary pituitary defect, so that the therapeutic implication of this synthesised group of releasing hormones is considerable.

GALACTORRHOEA is frequently due to a microadenoma (see ADENOMA) of the pituitary. DOPAMINE is the prolactin-release inhibiting hormone. Its duration of action is short so its therapeutic value is limited. However, BROMOCRIPTINE is a dopamine agonist with a more prolonged action and is e?ective treatment for galactorrhoea.

Thyroid gland The functions of the thyroid gland are controlled by the pituitary gland (see above) and the hypothalamus, situated in the brain. The thyroid, situated in the front of the neck below the LARYNX, helps to regulate the body’s METABOLISM. It comprises two lobes each side of the TRACHEA joined by an isthmus. Two types of secretory cells in the gland – follicular cells (the majority) and parafollicular cells – secrete, respectively, the iodine-containing hormones THYROXINE (T4) and TRI-IODOTHYRONINE (T3), and the hormone CALCITONIN. T3 and T4 help control metabolism and calcitonin, in conjunction with parathyroid hormone (see above), regulates the body’s calcium balance. De?ciencies in thyroid function produce HYPOTHYROIDISM and, in children, retarded development. Excess thyroid activity causes thyrotoxicosis. (See THYROID GLAND, DISEASES OF.)... endocrine glands

SIMPLE GOITRE A benign enlargement of the THYROID GLAND with normal production of hormone. It is ENDEMIC in certain geographical areas where there is IODINE de?ciency. Thus, if iodine intake is de?cient, the production of thyroid hormone is threatened and the anterior PITUITARY GLAND secretes increased amounts of thyrotrophic hormone with consequent overgrowth of the thyroid gland. Simple goitres in non-endemic areas may occur at puberty, during pregnancy and at the menopause, which are times of increased demand for thyroid hormone. The only e?ective treament is thyroid replacement therapy to suppress the enhanced production of thyrotrophic hormone. The prevalence of endemic goitre can be, and has been, reduced by the iodinisation of domestic salt in many countries. NODULAR GOITRES do not respond as well as the di?use goitres to THYROXINE treatment. They are usually the result of alternating episodes of hyperplasia and involution which lead to permanent thyroid enlargement. The only e?ective way of curing a nodular goitre is to excise it, and THYROIDECTOMY should be recommended if the goitre is causing pressure symptoms or if there is a suspicion of malignancy. LYMPHADENOID GOITRES are due to the production of ANTIBODIES against antigens (see ANTIGEN) in the thyroid gland. They are an example of an autoimmune disease. They tend to occur in the third and fourth decade and the gland is much ?rmer than the softer gland of a simple goitre. Lymphadenoid goitres respond to treatment with thyroxine. TOXIC GOITRES may occur in thyrotoxicosis (see below), although much less frequently autonomous nodules of a nodular goitre may be responsible for the increased production of thyroxine and thus cause thyrotoxicosis. Thyrotoxicosis is also an autoimmune disease in which an antibody is produced that stimulates the thyroid to produce excessive amounts of hormone, making the patient thyrotoxic.

Rarely, an enlarged gland may be the result of cancer in the thyroid.

Treatment A symptomless goitre may gradually disappear or be so small as not to merit treatment. If the goitre is large or is causing the patient di?culty in swallowing or breathing, it may need surgical removal by partial or total thyroidectomy. If the patient is de?cient in iodine, ?sh and iodised salt should be included in the diet.

Hyperthyroidism is a common disorder affecting 2–5 per cent of all females at some time in their lives. The most common cause – around 75 per cent of cases – is thyrotoxicosis (see below). An ADENOMA (or multiple adenomas) or nodules in the thyroid also cause hyperthyroidism. There are several other rare causes, including in?ammation caused by a virus, autoimune reactions and cancer. The symptoms of hyperthyroidism affect many of the body’s systems as a consequence of the much-increased metabolic rate.

Thyrotoxicosis is a syndrome consisting of di?use goitre (enlarged thyroid gland), over-activity of the gland and EXOPHTHALMOS (protruding eyes). Patients lose weight and develop an increased appetite, heat intolerance and sweating. They are anxious, irritable, hyperactive, suffer from TACHYCARDIA, breathlessness and muscle weakness and are sometimes depressed. The hyperthyroidism is due to the production of ANTIBODIES to the TSH receptor (see THYROTROPHIN-STIMULATING HORMONE (TSH)) which stimulate the receptor with resultant production of excess thyroid hormones. The goitre is due to antibodies that stimulate the growth of the thyroid gland. The exoph-

thalmos is due to another immunoglobulin called the ophthalmopathic immunoglobulin, which is an antibody to a retro-orbital antigen on the surface of the retro-orbital EYE muscles. This provokes in?ammation in the retro-orbital tissues which is associated with the accumulation of water and mucopolysaccharide which ?lls the orbit and causes the eye to protrude forwards.

Although thyrotoxicosis may affect any age-group, the peak incidence is in the third decade. Females are affected ten times as often as males; the prevalence in females is one in 500. As with many other autoimmune diseases, there is an increased prevalence of autoimmune thyroid disease in the relatives of patients with thyrotoxicosis. Some of these patients may have hypothyroidism (see below) and others, thyrotoxicosis. Patients with thyrotoxicosis may present with a goitre or with the eye signs or, most commonly, with the symptoms of excess thyroid hormone production. Thyroid hormone controls the metabolic rate of the body so that the symptoms of hyperthyroidism are those of excess metabolism.

The diagnosis of thyrotoxicosis is con?rmed by the measurement of the circulating levels of the two thyroid hormones, thyroxine and TRIIODOTHYRONINE.

Treatment There are several e?ective treatments for thyrotoxicosis. ANTITHYROID DRUGS These drugs inhibit the iodination of tyrosine and hence the formation of the thyroid hormones. The most commonly used drugs are carbimazole and propylthiouricil: these will control the excess production of thyroid hormones in virtually all cases. Once the patient’s thyroid is functioning normally, the dose can be reduced to a maintenance level and is usually continued for two years. The disadvantage of antithyroid drugs is that after two years’ treatment nearly half the patients will relapse and will then require more de?nitive therapy. PARTIAL THYROIDECTOMY Removal of three-quarters of the thyroid gland is e?ective treatment of thyrotoxicosis. It is the treatment of choice in those patients with large goitres. The patient must however be treated with medication so that they are euthyroid (have a normally functioning thyroid) before surgery is undertaken, or thyroid crisis and cardiac arrhythmias may complicate the operation. RADIOACTIVE IODINE THERAPY This has been in use for many years, and is an e?ective means of controlling hyperthyroidism. One of the disadvantages of radioactive iodine is that the incidence of hypothyroidism is much greater than with other forms of treatment. However, the management of hypothyroidism is simple and requires thyroxine tablets and regular monitoring for hypothyroidism. There is no evidence of any increased incidence of cancer of the thyroid or LEUKAEMIA following radio-iodine therapy. It has been the pattern in Britain to reserve radio-iodine treatment to those over the age of 35, or those whose prognosis is unlikely to be more than 30 years as a result of cardiac or respiratory disease. Radioactive iodine treatment should not be given to a seriously thyrotoxic patient. BETA-ADRENOCEPTOR-BLOCKING DRUGS Usually PROPRANOLOL HYDROCHLORIDE: useful for symptomatic treatment during the ?rst 4–8 weeks until the longer-term drugs have reduced thyroid activity.

Hypothyroidism A condition resulting from underactivity of the thyroid gland. One form, in which the skin and subcutaneous tissues thicken and result in a coarse appearance, is called myxoedema. The thyroid gland secretes two hormones – thyroxine and triiodothyronine – and these hormones are responsible for the metabolic activity of the body. Hypothyroidism may result from developmental abnormalities of the gland, or from a de?ciency of the enzymes necessary for the synthesis of the hormones. It may be a feature of endemic goitre and retarded development, but the most common cause of hypothyroidism is the autoimmune destruction of the thyroid known as chronic thyroiditis. It may also occur as a result of radio-iodine treatment of thyroid overactivity (see above) and is occasionally secondary to pituitary disease in which inadequate TSH production occurs. It is a common disorder, occurring in 14 per 1,000 females and one per 1,000 males. Most patients present between the age of 30 and 60 years.

Symptoms As thyroid hormones are responsible for the metabolic rate of the body, hypothyroidism usually presents with a general sluggishness: this affects both physical and mental activities. The intellectual functions become slow, the speech deliberate and the formation of ideas and the answers to questions take longer than in healthy people. Physical energy is reduced and patients frequently complain of lethargy and generalised muscle aches and pains. Patients become intolerant of the cold and the skin becomes dry and swollen. The LARYNX also becomes swollen and gives rise to a hoarseness of the voice. Most patients gain weight and develop constipation. The skin becomes dry and yellow due to the presence of increased carotene. Hair becomes thinned and brittle and even baldness may develop. Swelling of the soft tissues may give rise to a CARPAL TUNNEL SYNDROME and middle-ear deafness. The diagnosis is con?rmed by measuring the levels of thyroid hormones in the blood, which are low, and of the pituitary TSH which is raised in primary hypothyroidism.

Treatment consists of the administration of thyroxine. Although tri-iodothyronine is the metabolically active hormone, thyroxine is converted to tri-iodothyronine by the tissues of the body. Treatment should be started cautiously and slowly increased to 0·2 mg daily – the equivalent of the maximum output of the thyroid gland. If too large a dose is given initially, palpitations and tachycardia are likely to result; in the elderly, heart failure may be precipitated.

Congenital hypothyroidism Babies may be born hypothyroid as a result of having little or no functioning thyroid-gland tissue. In the developed world the condition is diagnosed by screening, all newborn babies having a blood test to analyse TSH levels. Those found positive have a repeat test and, if the diagnosis is con?rmed, start on thyroid replacement therapy within a few weeks of birth. As a result most of the ill-effects of cretinism can be avoided and the children lead normal lives.

Thyroiditis In?ammation of the thyroid gland. The acute form is usually caused by a bacterial infection elsewhere in the body: treatment with antibiotics is needed. Occasionally a virus may be the infectious agent. Hashimoto’s thyroiditis is an autoimmune disorder causing hypothyroidism (reduced activity of the gland). Subacute thyroiditis is in?ammation of unknown cause in which the gland becomes painful and the patient suffers fever, weight loss and malaise. It sometimes lasts for several months but is usually self-limiting.

Thyrotoxic adenoma A variety of thyrotoxicosis (see hyperthyroidism above) in which one of the nodules of a multinodular goitre becomes autonomous and secretes excess thyroid hormone. The symptoms that result are similar to those of thyrotoxicosis, but there are minor di?erences.

Treatment The ?rst line of treatment is to render the patient euthyroid by treatment with antithyroid drugs. Then the nodule should be removed surgically or destroyed using radioactive iodine.

Thyrotoxicosis A disorder of the thyroid gland in which excessive amounts of thyroid hormones are secreted into the bloodstream. Resultant symptoms are tachycardia, tremor, anxiety, sweating, increased appetite, weight loss and dislike of heat. (See hyperthyroidism above.)... goitre

These are fats similar to, and usually synthesized from, cholesterol, starting with Acetyl-CoA, moving through squalene, past lanosterol, into cholesterol, and, in the gonads and adrenal cortex, back to a number of steroid hormones. Nearly all of the classic hormones are proteins or smaller peptides; they don’t get inside a cell (the membrane keeps them out); instead, they bind to, and initiate, cell changes from the outside. The exceptions are the thyroxines (from the thyroid) and the steroid hormones. They move into the cell, bind with receptors, and initiate changes in the way a cell regenerates itself or synthesizes new compounds. Because the steroid hormones stimulate cell growth, either by changing the internal structure or increasing the rate of proliferation, they are often called anabolic steroids. Estrogen, an ovarian steroid, when secreted into the bloodstream, will be bound within a short time by internal receptors inside those cells that need estrogen for their growth; the unused portion is partially broken down, mostly in the liver, and partially stored in a less active form by adipose tissue. Since luteinizing hormone from the pituitary is surged in pulses an hour apart, the estrogen is also surged from the reacting ovaries, and by the time more estrogen is available, the binding cells need more; their program of synthesis has run out and needs to be started again. Of course, most steroid hormone reactions are less measured than this, but you get the idea.... steroid hormone

Also termed tetraiodothyronine, nicknamed is thyroxine. Secreted by the thyroid along with T3 (triiodothyronine...also called thyroxine), this thyroxine is mostly conjugated in the blood by TBG (thyroxine-binding globulin), whereas the more active T3 tends to float free. T4 is broken down to T3 and forms a stable feeder reserve, preventing rapid shifts in its more labile relative... t4

A hormone (see HORMONES) manufactured and released by the anterior part of the PITUITARY GLAND which stimulates the THYROID GLAND to manufacture and release thyroid hormones (THYROXINE and TRI-IODOTHYRONINE).... thyrotrophin-stimulating hormone (tsh)

(T3) The substance which exerts the physiological action of thyroid hormone (see THYROID GLAND). It is formed in the body cells by the de-iodination of THYROXINE (tetraiodothyronine) which is the active principle secreted by the thyroid gland. It has also been synthesised, and is now available for the treatment of hypothyroidism (see THYROID GLAND, DISEASES OF). It is three times as potent as thyroxine.... tri-iodothyronine

One of the AMINO ACIDS. Tyrosine is important in the production of CATECHOLAMINES, MELANIN and THYROXINE.... tyrosine

A congenital condition characterized by stunted growth and failure of normal development, and, in infants, coarse facial features. Cretinism results when the thyroid gland fails to produce or produces insufficient amounts of the thyroid hormone thyroxine at birth. Replacement therapy with thyroxine is a cure, provided the condition is recognized early. (See also hypothyroidism.)... cretinism

A synthetic version of the thyroid hormone thyroxine, used to treat hypothyroidism. Side effects, such as rapid heartbeat and tremor, may occur if the initial dose is too high.... levothyroxine

An element essential for formation of the thyroid hormones, triiodothyronine (T3) and thyroxine (T4), which control the rate of metabolism (internal chemistry) and growth and development. Dietary shortage may lead to goitre or hypothyroidism. Deficiency in the newborn can, if left untreated, lead to cretinism. Shortages are very rare in developed countries due to bread and table salt being fortified with iodide or iodate. Radioactive iodine is sometimes used to reduce thyroid gland activity in cases of thyrotoxicosis and in the treatment of thyroid cancer. Iodine compounds are used as antiseptics, in radiopaque contrast media in some X-ray procedures (see imaging techniques), and in some cough remedies.... iodine

A collective term for all the chemical processes that take place in the body. It is divided into catabolism (breaking down of complex substances into simpler ones) and anabolism (building up of complex substances from simpler ones). Usually, catabolism releases energy, while anabolism uses it.

The energy needed to keep the body functioning at rest is called the basal metabolic rate (BMR). It is measured in joules (or kilocalories) per square metre of body surface per hour. The BMR increases in response to factors such as stress, fear, exertion, and illness, and is controlled principally by various hormones, such as thyroxine, adrenaline (epinephrine), and insulin. (See also metabolism, inborn errors of; metabolic disorders.)... metabolism

n. a collection of inherited disorders of thyroid hormone synthesis resulting in low levels of *thyroxine and *triiodothyronine and high levels of *thyroid-stimulating hormone, with consequent *goitre formation. The result may be *cretinism with a goitre or milder forms of *hypothyroidism with a goitre. Several different stages of the production pathway for thyroid hormones can be affected.... dyshormonogenesis

(sick euthyroid syndrome) a syndrome characterized by alteration in the thyroid function tests in which the level of triiodothyronine is markedly reduced, thyroxine is slightly reduced, and thyroid-stimulating hormone is reduced or normal. This syndrome is commonly seen in nonthyroidal illness, due to altered metabolism and transport of the thyroid hormones, but can be mistaken for secondary *hypothyroidism.... euthyroid sick syndrome

see thyroxine.... levothyroxine sodium

n. 1. a dry firm waxy swelling of the skin and subcutaneous tissues found in patients with underactive thyroid glands (see hypothyroidism). 2. the clinical syndrome due to hypothyroidism in adult life, including coarsening of the skin, intolerance to cold, weight gain, and mental dullness. The symptoms are abolished with thyroxine treatment. —myxoedematous adj.... myxoedema

see blood pressure.

t

T3 see triiodothyronine.

T4 see thyroxine.... systolic pressure

“Brittle bones”. The Silent Epidemic. Weakness and softness of the bones due to wastage of minerals, chiefly calcium. Crippling, painful, deforming. ‘Bone-thinning’ leads to hundreds of thousands of crush and spontaneous fractures every year. Vertebra of the spine may collapse with loss of height and stooping. Sufferers show body levels of zinc about 25 per cent lower than normal. May run in families.

Affects women more than men by 10:1 especially after menopause, whether this is natural or due to destruction or removal of ovaries in early adult life.

By means of a calcium-rich diet after 35 years it is a preventable disease. Like so many degenerative diseases a common cause is widespread consumptions of refined, processed, chemicalised foods. It is possible that dental caries is in reality osteoporosis.

In men, alcohol is the chief cause. It wreaks its greatest havoc in women 10-15 years after the menopause. Increased calcium will not restore tissue already lost by wasting. Emphasis is therefore on prevention. It is estimated that a quarter of women over 50 in the West suffer bone loss after the menopause when reduced oestrogen speeds loss of calcium with possible bone damage to wrist, spine and especially hip. The chances of such fractures in women reaching seventy are one in two.

Vitamin D deficiency predisposes, as also does over-prescription of thyroxine for hypothyroid cases. Fat-free diets can break bones.

In menopausal women, increased bone loss is associated with disorders of the ovaries, which organs should receive treatment. Specially at risk are anorexic women with absence of periods. Secondary causes: hyperthyroidism, long-term use of steroids, liver disease, drugs (Tamoxifen, Antacids).

Common fractures are those of hips, spine and wrist. Wrist bone mineral content and grip strength are related. Squeezing a tennis ball hard three times each morning and evening reduces risk of fractures of the wrist.

Drinking of Lemon juice contributes to brittle bones. The habit of daily drinking of the juice causes enamel of teeth to crumble and the removal of calcium from the bones.

Cod Liver oil (chief of the iodised oils) reaches and nourishes cartilage, imparting increased elasticity which prevents degeneration.

Coffee. Two or more cups of coffee a day significantly reduces bone mineral density in women, but drinking milk each day can counter it.

Alternatives. Alfalfa, Black Cohosh, Chamomile, Clivers, Fennel, Dong quai, Fenugreek, Liquorice, Meadowsweet, Mullein, Pimpernel, Helonias, Plantain, Rest Harrow, Shepherd’s Purse, Silverweed, Toadflax, Unicorn root. Nettle tea.

Tea. Equal parts. Alfalfa, Comfrey leaves, Nettles. Mix. 2 teaspoons to each cup boiling water; infuse 5- 15 minutes; 1 cup thrice daily.

Decoction. Equal parts: Comfrey root, Irish Moss (for minerals), Horsetail. Mix. 3 heaped teaspoons to 1 pint (500ml) water gently simmered 20 minutes. Dose: 1 cup thrice daily.

Tablets/capsules. Bamboo gum, Helonias, Iceland Moss, Irish Moss for minerals, Kelp, Prickly Ash. Formula. Horsetail 2; Alfalfa 2; Helonias 1. Mix. Powders: 500mg (two 00 capsules or one-third teaspoon). Liquid extracts: 1 teaspoon. Tinctures: 2 teaspoons. Action is enhanced by taking in a cup of Fenugreek tea.

Comfrey decoction. 1 heaped teaspoon to cup water gently simmered 5 minutes. Strain when cold. Dose: 1 cup, to which is added 10 drops Tincture Helonias, morning and evening. Fenugreek seeds may be used as an alternative to Comfrey root. Comfrey and Fenugreek are osteo-protectives. For this condition the potential benefit of Comfrey outweighs possible risk.

Propolis. Regeneration of bone tissue.

Dr John Christopher. Mix powders: Horsetail 6, de-husked Oats 3; Comfrey root 4; Lobelia 4. Dose: quarter to half a teaspoon 2-3 times daily.

Diet. Fresh raw fruit and green vegetables. Consumption of raw bran (which contains calcium-binding phytic acid) and wholemeal bread should be suspended until recovery is advanced. Natural spring water. Fish and fish oils. Reject high salt intake which aggravates bone loss and places the skeleton at risk by creating increasing loss of calcium and phosphorus through the kidneys. Avoid soft drinks, alcohol. Heavy meat meals inhibit calcium metabolism. Incidence of the disease is lower in vegetarians. High protein. Supplements. Daily. Vitamin A, Vitamin B12 (50mcg); Vitamin C (500mg); Vitamin D, Vitamin E, Folic acid 200mcg; Vitamin B6 (50mg); Calcium citrate 1g; Magnesium citrate 500mg. Boron and Vitamin D. Zinc 15mg.

Calcium helps reduce risk of fracture particularly in menopausal women who may increase their daily intake to 800mg – Calcium citrate malate being more effective than the carbonate. Dried skimmed milk can supply up to 60 per cent of the recommended daily amount of Calcium.

Stop smoking.

Information. National Osteoporosis Society, PO Box 10, Radstock, Bath BA3 3YB, UK. Send SAE. ... osteoporosis

n. see thyroxine.... tetraiodothyronine

an iodine-containing substance, synthesized and secreted by the thyroid gland, that is essential for normal metabolic processes and mental and physical development. There are two thyroid hormones, *triiodothyronine and *thyroxine, which are formed from *thyroglobulin. Lack of these hormones gives rise to *cretinism in infants and *myxoedema in adults. Excessive production of thyroid hormones gives rise to *thyrotoxicosis.... thyroid hormone

(TSH, thyrotrophin) a hormone, synthesized and secreted by the anterior pituitary gland under the control of *thyrotrophin-releasing hormone, that stimulates activity of the thyroid gland. Raised levels of TSH are found in primary *hypothyroidism. Normal or low TSH levels in the presence of a low serum thyroxine are found in secondary hypothyroidism and the *euthyroid sick syndrome.... thyroid-stimulating hormone

(T3) n. the most metabolically active of the *thyroid hormones, which is mostly formed in the tissues from *thyroxine. A preparation of triiodothyronine (*liothyronine sodium) is administered by mouth or injection for treating underactivity of the thyroid.... triiodothyronine

Disorders of the thyroid gland may cause hyperthyroidism, hypothyroidism, or enlargement or distortion of the gland. Myxoedema, Graves’ disease, and Hashimoto’s thyroiditis are common disorders. Goitre may sometimes occur with no accompanying abnormality of thyroid function. In rare cases, the gland is absent at birth, producing severe cretinism. Sometimes it develops in an abnormal position in the neck, causing, in rare cases, difficulty in swallowing or breathing.

A genetic disorder may impair the thyroid’s ability to secrete hormones and goitre may result. Thyroid infection is uncommon and leads to thyroiditis. Viral infection can cause extreme pain and temporary hyperthyroidism. Hormonal changes during puberty or pregnancy may cause a degree of goitre temporarily. Hyperthyroidism due to excessive production of by the pituitary gland is rare but can occur as a result of a pituitary tumour.

Because iodine is necessary for the production of thyroid hormone, its deficiency may lead to goitre. Severe iodine deficiency in children may cause myxoedema. (See also thyroid cancer.)

thyroid hormones The 3 hormones produced by the thyroid gland are thyroxine (T4) and triiodothyronine (T3), which regulate metabolism, and calcitonin, which helps to regulate calcium levels in the body.... thyroid gland, disorders of

a life-threatening condition due to severe *hypothyroidism, which is often precipitated by an acute event, such as surgery, prolonged exposure to cold, infection, trauma, other severe illness, or sedative drugs. It manifests as hypothermia, slowing of the heart rate with a reduction in blood pressure and sometimes heart failure, pleural and peritoneal effusions, urinary retention, and a gradually reduced conscious state resulting in coma. Blood tests show hypothyroidism, *hyponatraemia, hypercholesterolaemia, retention of carbon dioxide, and anaemia. Treatment is with intravenous *thyroxine at a high dosage until the patient wakes up, when tablets can be administered. Support on a ventilator and intravenous fluids may be needed. Active slow rewarming should be undertaken.... myxoedema coma

the administration of an estimated amount of the radioactive isotope iodine-131 as a drink in order to treat an overactive thyroid gland (see thyrotoxicosis). The iodine concentrates in the thyroid and thus delivers its beta radiation locally, with little effect on other tissues. The gland will shrink and become euthyroid over the succeeding 8–12 weeks but there is a high incidence of subsequent hypothyroidism (up to 80%), which requires lifetime treatment with thyroxine. The treatment cannot be used if there is any suspicion of pregnancy, and the patient must stay away from young children and pregnant women for around 10 days after administration. Despite these drawbacks, radioactive iodine remains a popular form of treatment for any cause of hyperthyroidism.... radioactive iodine therapy