Function of the Thyroid Gland

The thyroid gland lies on either side of the trachea in the anterior neck region and consists of bilateral lobes that are connected by a central isthmus. The entire gland weighs approximately 15 to 20 g and receives a 

The thyroid gland synthesizes two primary hormones thyroxine and triiodothyronine. A discussion of the synthesis and function of these hormones follows. 

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FIGURE 4.11 Negative feedback loop regulating the function of the thyroid gland. 

Thyrotropin-releasing hormone is one of several small peptide hormones secreted by the anterior lobe of the pituitary gland. These are the master" hormones that function to stimulate hormone secretion from other endocrine glands. Thyrotropin stimulates the functioning of the thyroid gland. 

The activity of an iodine-131 source (ty2 = 8.05 d), which is used to monitor the functioning of the thyroid gland, is 500 Bq. How long will it be before the activity is 10 disintegrations per second ... 

Iodine is necessary for the proper function of the thyroid gland in humans. Dietary deficiencies can be avoided by the occasional consumption of seafood or by using iodized salt, which combines common table salt (NaCl) with potassium iodide (KI). Iodine is a useful antiseptic, either as tincture of iodine (an alcohol solution of I2), or as an aqueous solution of provi-done iodine (Betadine). see also Halogens Inorganic Chemistry. 

Fluorine (F) and its metabolites are of importance in protecting teeth from caries. Fluorine is included in calcium hydroxyapatite, and it promotes the precipitation of calcium phosphate Ca(P03)2 and accelerates the remineralization. The necessary concentration of Fluorine added to drinking water to prevent caries is approximately 1 mg/L. Application of higher Fluorine concentrations (above 8 mg/L) leads to fluorosis. This is a disease that is characterized by a disturbance in the function of the thyroid gland. A long-term application of fluorine leads to intensive mineralization (possible precipitation of calcium sulfate), deformation of bones with possible accretion, and calcification of the connections. 

Iodine (I) has a great role in the function of the thyroid gland. It takes part in a complex biochemical synthesis schema and interacts with hormones. Deficiency of iodine is characterized weakness, feelings of cold and dryness, and yellow-colored skin. The treatment of these symptoms is achieved with iodine or thyroid hormones. 

Thyroid hormones are used either to replace the failing function of the thyroid gland (spontaneous or drug-induced) or to suppress the endocrine function of abnormal thyroid tissues (especially non-toxic struma or goiter or after thyroidectomy for thyroid neoplasms). Although there are abnormalities of the peripheral metabolism of thyroid hormones in some forms of undernutrition or overnutrition, thyroid drug therapy cannot be considered a safe way of treating obesity. 

TSH (also called thyrotropin), which is secreted by the pituitary, plays a central role in the regulation of growth and function of the thyroid gland. TSH receptors are functionally coupled to G-proteins thus, the extracellular stimulus by TSH is transduced into intracellular signals mediated by a number of G-proteins. Activation of Gs-protein results in the stimulation of the adenylate cyclase-cAMP-protein phosphorylation cascade. Other G-proteins coupled to TSH-receptor activation include Gg-protein, which mediates the phospholipase C-phosphatidylinositol 4,5-bisphosphate-Ca + signaling pathway (see Chapter 30 for a detailed discussion). 

Iodine is a mineral that is required for the proper function of the thyroid gland. The thyroid gland extracts iodine from nutrients and incorporates it into various hormones. The once-common condition of goiter, an enlargement of the thyroid gland, is an abnormality that results from an effort to compensate for low iodine intake. Goiter can be prevented if iodine is included in the diet. Seafood is one of the best sources of iodine. In areas where seafood is not available, dietary iodine is easily obtained in the form of iodized salt, found in most grocery stores. 

Chromium assists in the metabolism of sugars, cobalt is present in vitamin B.,2/ iodine is necessary for the proper functioning of the thyroid gland, manganese plays a role in maintaining proper calcium levels in the bones, and copper is involved in the production of red blood cells. 

Radiotracers also have important uses in medicine. Iodine-131, for example, is commonly used to detect diseases associated with the thyroid gland. If a problem is suspected, the patient will drink a solution containing a small amount of iodine-131. After the iodine is absorbed, the amount of iodine taken up by the thyroid is measured and used to monitor the functioning of the thyroid gland. 

Iodine is an essential micronutrient in animals and humans, necessary for the production of thyroid hormones and for the proper functioning of the thyroid gland, and deflciencies can lead to severe metaboflc disorders. As reported by the World Health Organization in 1999, iodine deflciency is a significant public health problem in 130 countries, with one-third of the worlds population estimated to be at risk. Furthermore, because radioactive iodine is concentrated in the human thyroid (VanMiddlesworth et ai, 2000), an uncontrolled release of radioactive iodine could constitute a direct threat to human populations. 

The function of the thyroid gland is to take iodine, found in many foods, and convert it into thyroid hormones thyroxine (TJ and triiodothyronine (T3). Thyroid cells are the only cells in the body which can absorb iodine. These cells combine iodine and the amino acid tyrosine to make T3 and T4. T3 and T4 are then released into the blood stream and are transported throughout the body, where they control metabolism (conversion of oxygen and calories to energy). Every cell in the body depends on thyroid hormones for regulation of their metabolism. The normal thyroid gland produces about 80% T4 and about 20% T3, however, T3 possesses about four times the hormone strength of T4. 

Iodine is essential for proper functioning of the thyroid gland. The thyroid cells have the ability to take up iodine and do not distinguish between stable and radioactive iodine. The metabolism, biodistribution and excretion are the same as for ordinary iodine. 

Iodine is essential for the normal development of all animals and man. Its basic biological importance is indicated by the fact that the tadpole will not undergo metamorphosis into the frog without the function of the thyroid gland in secreting the iodine-containing thyroid hormones. 

The thyroid is a small gland located in a person s neck on either side of the breathing tube (trachea). The thyroid has two parts, a right lobe and a left lobe, that are connected by a small strip of tissue called the isthmus. The main function of the thyroid gland is to create, store, and release thyroid hormones. These hormones regulate the body s metabolism. 

We all know that certain chemical elements, such as calcium, carbon, nitrogen, phosphorus, and iron, are essential for humans to live. However, many other elements that are present in tiny amounts in the human body are also essential to life. Examples are chromium, cobalt, iodine, manganese, and copper. Chromium assists in the metabolism of sugars, cobalt is present in vitamin B12, iodine is necessary for the proper functioning of the thyroid gland, manganese appears to play a role in maintaining the proper calcium levels in bones, and copper is involved in the production of red blood cells. 

Recent work on the three main functions of the thyroid gland— the collection of iodide from the plasma, the transformation of iodide into organically bound iodine and the release of the hormone into the circulation—has been reviewed. 

Miscellaneous observations Include the fact that the antiinflammatory effect of NAA in the rat appears to require a normal functioning of the thyroid gland.35,36 increased protocollagen prollne hydroj lase activity has been noted in rheumatoid synovial tissue. The excretion of hydroxy-pro line in urine corresponded with the activity and extent of the arthritic process.38 Antiinflammatory agents reduced the hydro proline excretion. 

LEARNING CHECK 10.7 Iodine-123 is a radioisotope used to diagnose the function of the thyroid gland. It has a half-Ufe of 13.3 hours. What fraction of a diagnostic dose of iodine-123 would be present in a patient 79.8 hours (a little over 3 days) after it was administered ... 

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