Thyroid Hormones

Thyroid Hormones 

Definition

Thyroid hormones are artificially made hormones that make up for a lack of natural hormones produced by the thyroid gland.

Purpose

The thyroid gland, a butterfly-shaped structure in the lower part of the neck, normally produces a hormone called thyroxine. This hormone controls the rate of metabolism—all the physical and chemical processes that occur in cells to allow growth and maintain body functions. When the thyroid gland does not produce enough thyroxine, body processes slow down. People with underactive thyroid glands feel unusually tired and may gain weight even though they eat less. They may also have trouble staying warm and may have other symptoms, such as dry skin, dry hair, and a puffy face. By making up for the lack of natural thyroxine and bringing the rate of metabolism back to normal, artificially made thyroid hormone improves these symptoms.

Thyroid hormones also may be used to treat goiter (enlarged thyroid gland) and certain types of thyroid cancer.

Description

Thyroid hormones, also called thyroid drugs, are available only with a physician's prescription. They are sold in tablet form. A commonly used thyroid hormone is levothyroxine (Synthroid, Levoxyl, Levothroid).

Recommended dosage

For adults and teenagers, the usual starting dose of levothyroxine tablets is 0.0125 mg (12.5 micrograms) to 0.05 mg (50 micrograms) per day. The physician who prescribes the medicine may gradually increase the dose over time.

For children, the dose depends on body weight and must be determined by a physician.

Taking thyroid hormones exactly as directed is very important. The physician who prescribes the medicine will figure out exactly how much of the medicine a patient needs. Taking too much or too little can make the thyroid gland overactive or underactive.

This medicine should be taken at the same time every day.

Precautions

People who take thyroid hormones because their thyroid glands do not produce enough natural hormone may need to take the medicine for the rest of their lives. Seeing a physician regularly while taking this medicine is important. The physician will make sure that the medicine is working and that the dosage is correct.

In patients with certain kinds of heart disease, this medicine may cause chest pains and shortness of breath during exercise. People who have this problem should be careful not to exert themselves too much.

Anyone who is taking thyroid hormones should be sure to tell the health care professional in charge before having any surgical or dental procedures or receiving emergency treatment.

This medicine is safe to take during pregnancy, but the dosage may need to be changed. Women who are pregnant should check with their physicians to make sure they are taking the proper dosage.

Anyone who has had unusual reactions to thyroid hormones in the past should let his or her physician know before taking the drugs again. The physician should also be told about any allergies to foods, dyes, preservatives, or other substances.

Before using thyroid hormones, people with any of these medical problems should make sure their physicians are aware of their conditions:

• heart disease
• high blood pressure
• hardening of the arteries
• diabetes
• history of overactive thyroid
• underactive adrenal gland
• underactive pituitary gland

Side effects

This medicine usually does not cause side effects if the dosage is right. Certain symptoms may be signs that the dose needs to be changed. Check with a physician if any of these symptoms occur:

• headache
• fever
• diarrhea
• vomiting
• changes in appetite
• weight loss
• changes in menstrual period
• tremors of the hands
• leg cramps
• increased sensitivity to heat
• sweating
• irritability
• nervousness
• sleep problems

Other side effects are possible. Anyone who has unusual symptoms while taking thyroid hormones should get in touch with his or her physician.

Interactions

Thyroid hormones may interact with other medicines. This may increase or decrease the effects of the thyroid medicine and may interfere with treatment. Anyone who takes thyroid hormones should not take any other prescription or nonprescription (over-the-counter) medicines without the approval of his or her physician. Among the drugs that may interact with thyroid hormones are:

• Medicine for colds, hay fever, and other allergies
• Medicine for asthma and other breathing problems
• Medicine for diabetes
• Blood thinners
• Amphetamines
• Diet pills (appetite suppressants)
• Cholesterol-lowering drugs such as cholestyramine (Questran) and colestipol (Colestid).

Key terms

Adrenal glands — A pair of glands located next to the kidneys. The adrenal glands produce hormones that control many body functions.

Hormone — A chemical that is produced in one part of the body and then travels through the bloodstream to another part of the body where it has its effect.

Pituitary gland — A pea-sized gland at the base of the brain that produces many hormones that affect growth and body functions.

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hormone /hor·mone/ (hor´mōn) a chemical substance produced in the body which has a specific regulatory effect on the activity of certain cells or a certain organ or organs.hormo´nal

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adrenocortical hormone 

1. any of the corticosteroids elaborated by the adrenal cortex, the major ones being the glucocorticoids and mineralocorticoids, and including some androgens, progesterone, and perhaps estrogens.

2. corticosteroid.

adrenocorticotropic hormone  (ACTH) corticotropin.

adrenomedullary hormones  substances secreted by the adrenal medulla, including epinephrine and norepinephrine.

androgenic hormone  androgen.

anterior pituitary hormones  those produced in the adenohypophysis (anterior pituitary), including corticotropin, follicle-stimulating hormone, growth hormone, luteinizing hormone, prolactin, and thyrotropin.

antidiuretic hormone  vasopressin.

cortical hormone  adrenocortical h.

corticotropin-releasing hormone  (CRH) a neuropeptide elaborated mainly by the median eminence of the hypothalamus, but also by the pancreas and brain, that stimulates the secretion of corticotropin.

ectopic hormone  one released from a neoplasm or cells outside the usual source of the hormone.

eutopic hormone  one released from its usual site or from a neoplasm of that tissue.

fibroblast growth hormone  a peptide hormone secreted by the adenohypophysis that is a potent mitogen of vascular endothelial cells and a regulator of tissue vascularization.

follicle-stimulating hormone  (FSH) one of the gonadotropic hormones of the adenohypophysis; it stimulates ovarian follicle growth and maturation, estrogen secretion, and endometrial changes characteristic of the first portion of the menstrual cycle in females, and stimulates spermatogenesis in males.

follicle-stimulating hormone–releasing hormone  (FSH-RH) luteinizing hormone

gonadotropic hormone  gonadotropin.

gonadotropin-releasing hormone  (Gn-RH)

1. luteinizing hormone

2. any hypothalamic factor that stimulates release of both follicle-stimulating hormone and luteinizing hormone.

growth hormone  (GH) any of several related hormones secreted by the adenohypophysis that directly influence protein, carbohydrate, and lipid metabolism and control the rate of skeletal and visceral growth; used pharmaceutically as somatrem and somatropin.

growth hormone–releasing hormone  (GH-RH) one elaborated by the hypothalamus, stimulating release of growth hormone from the adenohypophysis.

inhibiting hormones  hormones elaborated by one body structure that inhibit release of hormones from another structure; applied to substances of established clinical identity, while those whose chemical structure is still unknown are called inhibiting factors.

interstitial cell–stimulating hormone  luteinizing h.

lactation hormone , lactogenic hormone prolactin.

local hormone  a substance with hormonelike properties that acts at an anatomically restricted site.

luteinizing hormone  (LH) a gonadotropin of the adenohypophysis, acting with follicle-stimulating hormone in females to promote ovulation as well as secretion of androgens and progesterone. It instigates and maintains the secretory portion of the menstrual cycle and is concerned with corpus luteum formation. In males, it stimulates the development and functional activity of testicular Leydig cells.

luteinizing hormone–releasing hormone  (LH-RH) a glycoprotein gonadotropic hormone of the adenohypophysis that acts with follicle-stimulating hormone to promote ovulation and promotes secretion of androgen and progesterone. A preparation of the salts is used in the differential diagnosis of hypothalamic, pituitary, and gonadal dysfunction and in the treatment of some forms of infertility and hypogonadism.

melanocyte-stimulating hormone , melanophore-stimulating hormone (MSH) one of several peptides secreted by the anterior pituitary in humans and in the rhomboid fossa in lower vertebrates, influencing melanin formation and deposition in the body and causing color changes in the skin of amphibians, fishes, and reptiles.

neurohypophysial hormones  posterior pituitary h's.

ovarian hormones  those secreted by the ovary, such as estrogens and progestational agents.

parathyroid hormone  a polypeptide hormone secreted by the parathyroid glands, which influences calcium and phosphorus metabolism and bone formation.

placental hormones  those produced by the placenta during pregnancy, including chorionic gonadotropin and other substances having estrogenic, progestational, or adrenocorticoid activity.

plant hormone  phytohormone.

posterior pituitary hormones  those released from the neurohypophysis (posterior pituitary), including oxytocin and vasopressin.

progestational hormone 

1. progesterone.

2. see under agent.

releasing hormones  hormones elaborated in one structure that cause the release of hormones from another structure; applied to substances of established chemical identity, while those whose chemical structure is unknown are called releasing factors.

sex hormones  the estrogens and androgens considered together.

somatotrophic hormone , somatotropic hormone growth h.

somatotropin-releasing hormone  (SRH) growth hormone

steroid hormones  those that are biologically active steroids; they are secreted by the adrenal cortex, testis, ovary, and placenta and include the progestogens, glucocorticoids, mineralocorticoids, androgens, and estrogens.

thyroid hormones  thyroxine, calcitonin, and triiodothyronine; in the singular, thyroxine and/or triiodothyronine.

thyroid-stimulating hormone  (TSH), thyrotropic hormone thyrotropin.

thyrotropin-releasing hormone  (TRH) a tripeptide hormone of the hypothalamus, which stimulates release of thyrotropin from the adenohypophysis and also acts as a prolactin-releasing factor. It is used in diagnosis of mild hyperthyroidism and Graves' disease, and in differentiating among primary, secondary, and tertiary hypothyroidism. A synthetic preparation is called protirelin.

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hormone(s) (hôr´mōn[z]),

n.pl the biochemical secretions of the endocrine glands that, in relatively small quantities, partially regulate the physiologic activity of the tissues, organs, organ systems, and other endocrine glands, and of the nervous system itself. Its secretions are conducted and distributed throughout the body by the circulation of the bloodstream and tissue fluids.

hormones, adenohypophyseal,

n.pl the hormones secreted by the adenohypophysis. Includes seven distinct hormones: somatotropin (STH), thyrotropin (TSH), prolactin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), melanocyte-stimulating hormone (MSH), and adrenocorticotropic hormone (ACTH).

hormones, adrenal medullary,

n.pl the hormones secreted by adrenal medulla, including two catecholamines: epinephrine and norepinephrine.

hormones, adrenocortical,

n the steroid hormones secreted by the adrenal cortex that are biologically active in one or more of the following states: stress, inflammation, metabolism of carbohydrates, proteins, electrolytes, and water.

hormones, adrenocorticotropic,

n See ACTH.

hormones, adrenotropic,

n See ACTH.

hormones, anabolic,

n.pl the hormones that decrease blood glucose; an example is insulin. See also anabolic steroids.

hormones, androgenic,

n.pl See hormones, sex, male.

hormones, anterior pituitary-like,

n See hormone, pregnancy.

hormones, antidiabetic,

n See insulin.

hormones, antidiuretic (ADH, vasopressin),

n a hormone of the posterior pituitary gland that encourages resorption of water by acting on the epithelial cells of the distal portion of the renal tubule. It raises blood pressure by its effect on the peripheral blood vessels and exerts an antidiuretic effect (antifacultative resorption of water in the renal tubules). An absence of antidiuretic hormone causes diabetes insipidus.

hormones, antiinflammatory,

n.pl See glucocorticoids.

hormones, catabolic,

n.pl the hormones that increase blood glucose; examples include glucagon, epinephrine, steroid and growth hormones, and thyroxine.

hormones, chorionic gonadotropic,

n a glycoprotein secreted by placental tissue early in normal pregnancy. This protein is also found in the urine or blood in association with chorioepitheliomas and some neoplastic diseases of the testes.

hormones, corticosteroid,

n See steroid, adrenocortical.

hormones, corticotropic,

n the ovarian or adrenal hormones (e.g., estradiol, estrone, estriol) that are capable of stimulating changes of a cyclic nature in the genital system. One of the ovarian or adrenal hormones capable of affecting the cyclic changes of the female genital system. See also ACTH.

hormones, female sex,

n.pl the hormones secreted by the ovary. They include two main types: the follicular, or estrogenic, hormones produced by the graafian follicle, and the progestational hormones from the corpus luteum.

hormones, follicle-stimulating,

a pituitary tropic hormone that promotes the growth and maturation of the ovarian follicle and, with other gonadotropins, induces secretion of estrogens and possibly spermatogenesis.

hormones, gastrointestinal,

n the hormones that regulate motor and secretory activity of the digestive organs; that is, gastrin, secretin, and cholecystokinin.

hormones, gonadotropic,

n See gonadotropin.

hormones, growth (somatotropic hormone, somatotropin),

n a hormone that is secreted by the anterior lobe of the pituitary gland and that exerts an influence on skeletal growth. As long as the growth apparatus is functional, it is responsive to the effects of the hormone.

hormones, ketogenic,

n the term used to describe a factor of the anterior pituitary hormone responsible for ketogenic effect. It is probably not an entity differing from known pituitary hormones.

hormones, lactogenic (galactin, mammotropin, prolactin),

n a pituitary hormone that stimulates lactation.

hormones, luteal,

n See hormones, progestational.

hormones, luteinizing,

n a pituitary hormone that causes ovulation and development of the corpus luteum from the mature graafian follicle. It is called an
interstitial cell and stimulating hormone because of its action on the testis in maintaining spermatogenesis and because of its role in the development of accessory sex organs.

hormones, male sex (androgenic hormone, C-19 steroids),

n.pl the hormones found in the testes, urine, and blood. Included are testosterone found in the testes, andosterone excreted into the urine, and dehydro-3-epiandrosterone found in the blood.

hormones, melanocyte-stimulating (MSH, intermedin),

n a hormone of the middle lobe of the pituitary gland that increases melanin deposition by the melanocytes of the skin.

hormones, N,

n See hormone, nitrogen and steroid, C-19 cortico.

hormones, neurohypophyseal,

n.pl the octapeptides of the neural lobe: oxytocin and vasopressin.

hormones, nitrogen (N hormone),

n.pl the C-19 corticosteroids that have androgenic and protein anabolic effects.

hormones, parathyroid,

n the secretory product of the parathyroid glands that promotes bone resorption and increases renal resorption of calcium and magnesium and diminishes that of phosphate. Excessive secretion produces generalized bone resorption, formation of fibrous marrow in the spongiosa, and, in young individuals, hypocalcification of the teeth.

hormones, pituitary,

n.pl the hormones of the anterior lobe of the pituitary gland, including the growth hormones (somatotropin 1, lactogenic hormone, prolactin, galactin, mammotropin) and pituitary tropins (gonadotropins, thyrotropic hormone, and ACTH). Whether or not a true diabetogenic pituitary hormone exists is a question. The melanocyte-stimulating hormone is secreted by the middle lobe of the pituitary gland, and vasopressin and oxytocin are secreted by the posterior lobe of the pituitary gland.

hormones, pregnancy (anterior pituitary-like hormone, antuitrin S, chorionic gonadotropin),

n a gonadotropic hormone found in the urine during pregnancy; it is a product of the very early placenta.

hormones, progestational (luteal hor-mone),

n.pl the hormones produced during the phase of the menstrual cycle just preceding menstruation. Includes progesterone, pregnanediol, and pregneninolone.

hormones, proinflammatory,

n See mineralocorticoids.

hormones, “S” (glucocorticoid factor, sugar hormone),

n a factor in the secretions of the adrenal cortex related to the regulation of carbohydrate metabolism.

hormones, sex,

n.pl the steroid hormones that are produced by the testes and ovaries and that control secondary sex characteristics, the reproductive cycle, development of the accessory reproductive cycle, and development of the accessory reproductive organs. Also included are the gonadotropins produced by the pituitary gland.

hormones, somatotropic,

n See hormone, growth.

hormones, steroid,

n.pl a group of biologically active organic compounds that are secreted by the adrenal cortex, testes, ovary, and placenta, and that have in common a cyclopentanoperhydrophenanthrene nucleus.

hormones, sugar,

n See hormone, “S” and steroid, C-21 cortico-.

hormones, testicular,

n.pl the hormones elaborated by the testes (mainly testosterone) that promote the growth and function of the male genitalia and secondary sex characteristics and that have potent protein anabolic effects.

hormones, thyroid,

n.pl the hormonal variants, including thyroxin and triiodothyronine, derived from the thyroid gland. They act as a catalyst for oxidative processes of the body cell and thus regulate the rates of body metabolism and stimulate body growth and maturation.

hormones, thyroid, thyroid-stimulating,

n See hormone, thyrotropic.

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thyroid

1. resembling a shield.

2. the thyroid gland (see below) secreting thyroid hormones (see below).

3. a pharmaceutical preparation of cleaned, dried, powdered thyroid gland, obtained from those domesticated animals used for food by humans.

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accessory thyroid

an additional thyroid located anywhere from the larynx to diaphragm, e.g. intrapericordial aorta; may be sufficient to supply the patient's need of thyroid hormone. Most common in dogs.

thyroid C cell

see c cell.

thyroid cartilage

the shield-shaped cartilage of the larynx.

thyroid diverticulum

primordium of the thyroid gland; appears as an outgrowth of the foregut between the first two pharyngeal pouches. This tube of epithelial cells grows ventrally into mesenchyme; the tube becomes the thyroglossal duct, the tip divides into two lobes, the thyroid glands.

thyroid dysfunction

see hypothyroidism, hyperthyroidism.

ectopic thyroid

migration of thyroid diverticulum tissue to aberrant sites occurs, e.g. thyroid tissue in the thymus. These cause no apparent abnormality.

thyroid extract

a pharmaceutical substance derived from thyroid glands, used in the treatment of hypothyroidism. See thyroid (3) (above).

thyroid function tests

used to assess the functional capacity of the thyroid glands; most commonly employed in dogs and cats. Include plasma T₄, plasma T₃, free T₄ radioiodine uptake, and TSH response tests.

thyroid gland

the largest of the endocrine glands, situated in the neck caudal to the larynx. It produces hormones (see below) that are vital in maintaining normal growth and metabolism. It also serves as a storehouse for iodine.

Microscopic appearance of the thyroid gland. By permission from Guyton R, Hall JE, Textbook of Medical Physiology, Saunders, 2000

thyroid hormones

iodothyronines secreted by the thyroid gland, principally thyroxine (tetraiodothyronine, T₄) and tri-iodothyronine (T₃); derived from iodination of tyrosyl residues in thyroglobulin. The pharmaceutical names for T₄ and T₃ are levothyroxine and liothyronine, respectively. Regulate basal metabolic rate.

thyroid parafollicular cell

see c cell.

thyroid radioiodine uptake

used as a thyroid function test but superseded these days by estimates of T₄ (thyroxine).

thyroid-stimulating hormone (TSH)

see thyrotropin.

thyroid tumor

mostly follicular adenomas in old-aged dogs, cats and horses; papillary adenomas are rare.

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Patient discussion about Thyroid Hormones.

Q. Has anyone tried natural hormones for hypo-thyroidism or fibromyalgia? I am on the low normal range for hypo-thyroidism (do not take meds for) and was diagnosed years ago with fibromyalgia. I take Ultram for the pain which also helps my fatigue factor but I still feel so sluggish sometimes and just want to sleep. I'm on an anti-depressant as it is. I've been hearing more about natural hormone therapy for these conditions and was wondering if anyone out there has tried this.

A. The Ultram and the anti-depressants do that and as for the natural hormone treatments they don't really work. The Gulf War that gave me hypo-thyroid and hypo-prolactimia which is the Pituitary Gland acting up. On top of the fibro,fatique,pain and recovering from arsenic poison I was put on hormone treatments and it made things worse. I blew up like a balloon, I was still tired and it never corrected the problem with my glands. I tried everything out there and I wasn't getting any better until now. A friend of mine told me of this product called Vitalitea and that it could help me.I was desperate to get my health back and boy did I. Go to Ai3global.com/greentea and click on product and wellness and read it. Check out the www on the healing properties of quality green tea and not the stuff you by at the local store. My fatique, and chronic pain is gone. My Fibromyalgia is so, so mild. I do fun things again after 7 year of suffering. You won't regret it. It is all natural.