Iodine - Thyroid Gland

Figure 8.2 The person in this photograph suffers from a swelling of the thyroid gland. Iodine is responsible for regulating the health of this gland.

Iodine - The importance of oxidation-state speciation of radioiodine was recognised at a very early stage because of its ability to accumulate in and cause damage to the human thyroid gland. Iodine-131 (t1/2 = 8.04 days) would therefore be... 

The neutral isotope of iodine is an essential element in the human body most of the iodine-127 is located in the thyroid gland. Iodine s radioactive isotope, iodine-131, is readily absorbed in the body, where it becomes concentrated in the thyroid gland and may produce cancers. Exposure to radioactive iodine is an increasing concern since it is produced by fission reactions in nuclear reactors and by nuclear weapons tests. 

In areas where there is also low iodine in the diet a further complication may arise. The thiocyanate that is formed from the cyanide inhibits the uptake of iodine into the thyroid gland. Iodine is used to make hormones that regulate the metabolism of the body, and its deficiency leads to goitre (enlarged thyroid) and cretinism (mental retardation) in the offspring of women with the disorder. 

Tab. 9.4-24 Effect of iodine deficiency of goats, sheep and cattle on thyroid gland iodine content (pg or mg)...

In the thyroid gland, iodine treatment arrested the cell cycle at the GO/Gl and G2/M phases (Tramontano et al.. 

Iodine is an essential element to humans and presents in the human body in minute amounts (15-20mg in adults), of which more than 80% exists in the thyroid gland. Iodine in the human body mainly comes from food intake and inhalation of atmospheric iodine. In the thyroid, iodine is added to the essential amino acid thyroxine residue on thyroglobulin. 

The primary inherited hypothyroidism characterized by significantly reduced T4 levels(32), reduced thyroid gland T4 (30), reduced thyroid gland iodine iptake (30), and elevated serum TSH-like activity (31) ... 

Synthesis of thyroid hormones has several stages. In the thyroid gland, iodine ions are oxidised to the active form (cation 1+) by the action of a specific thyroid peroxidase (thyroperoxidase), which reacts with tyrosyl residues of thyroglobulin to form 3-iodotyrosine. Subsequent iodisation of 3-iodotyrosine yields 3,5-diiodotyrosine. The condensation reaction of 3,5-diiodotyrosine with 3-iodotyrosine in the colloid of the thyroid follicle yields 3,5,3 -triiodothyronine. Two molecules of 3,5-diiodotyrosine combine to form thyroxine. These hormones, bound to thyroglobulin, are then released into the blood as a result of thyroglobulin proteolysis regulated by thyrotropin. In the blood, normal concentrations of 3,5,3 -triiodothyronine can vary by as much as 1-1.5 p,g/l, and thyroxine concentrations range from 60 to 120 (xg/l. 

Iodine has many radioactive isotopes. Iodine-123 is a radioactive isotope used for obtaining images of the thyroid gland. Iodine-123 is administered to patients in the form of sodium iodide capsules that contain I ions. Determine the number of neutrons, protons, and electrons in a single 1 ion. 

Iodine occurs to a minute extent (less than 0.001 %) in sea water, but is found in greater concentration, combined in organic form, in certain seaweeds, in oysters and in cod livers. Crude Chile saltpetre, or caliche contains small amounts of sodium iodate, NalOj. from which iodine can be obtained (see below). Some insoluble iodides, for example liiose of silver and mercury(II), occur in Mexico. Iodine is found in the human body in the compound thyroxin in the thyroid gland deficiency of iodine in diet causes enlargement of this gland (goitre). 

Thirty isotopes are recognized. Only one stable isotope, 1271 is found in nature. The artificial radioisotope 1311, with a half-life of 8 days, has been used in treating the thyroid gland. The most common compounds are the iodides of sodium and potassium (KI) and the iodates (KIOs). Lack of iodine is the cause of goiter. 

The "time of flight" mass spectrometer has been used to confirm that this highly radioactive halogen behaves chemically very much like other halogens, particularly iodine. Astatine is said to be more metallic than iodine, and, like iodine, it probably accumulates in the thyroid gland. Workers at the Brookhaven National Laboratory have recently used reactive scattering in crossed molecular beams to identify and measure elementary reactions involving astatine. 

To prevent radioactive iodides from lodging in the thyroid gland during exposure to excessive radiation, a potential appHcation of iodine acting as a thyroid-blocker has arisen. Eor this purpose potassium iodide was recommended (66). 

Iodine. Of the 10—20 mg of iodine in the adult body, 70—80 wt % is in the thyroid gland (see Thyroid and antithyroid preparations). The essentiahty of iodine, present in all tissues, depends solely on utilisation by the thyroid gland to produce thyroxine [51-48-9] and related compounds. Well-known consequences of faulty thyroid function are hypothyroidism, hyperthyroidism, and goiter. Dietary iodine is obtained from eating seafoods and kelp and from using iodized salt. 

The main role of the human thyroid gland is production of thyroid hormones (iodinated amino acids), essential for adequate growth, development, and energy metaboHsm (1 6). Thyroid underfunction is an occurrence that can be treated successfully with thyroid preparations. In addition, the thyroid secretes calcitonin (also known as thyrocalcitonin), a polypeptide that lowers excessively high calcium blood levels. Thyroid hyperfunction, another important clinical entity, can be corrected by treatment with a variety of substances known as antithyroid dmgs. 

Sodium Levothyroxine. As one of the active principles of the thyroid gland, sodium levothyroxine [55-03-8] (levothyroxine sodium) can be obtained either from the thyroid glands of domesticated animals (10) or synthetically. It should contain 61.6—65.5% iodine, corresponding to 100 3% of the pure salt calculated on an anhydrous basis. Its chiral purity must also be ascertained because partial racemi2ation may occur during synthesis and because dl-T is available commercially. Sodium levothyroxine melts with decomposition at ca 235°C. It is prepared as pentahydrate [6106-07-6] from... 

If the necessary iodine input is insufficient the thyroid gland enlarges in an attempt to gamer more iodine addition of 0.01% Nal to table salt (iodized salt) prevents this condition. Tincture of iodine is a useful antiseptic. 

Iodine-131 is used in the treatment of tumors in the thyroid gland. Its half-life is 8.1 days. Suppose that, due to a shipment delay, the 1-131 in a hospital s pharmacy is 2.0 days old. 

Strong iodide solutions act by decreasing the vascularity of the thyroid gland by rapidly inhibiting the release of the thyroid hormones. Radioactive iodine is distributed within the cellular fluid and excreted. The radioactive isotope accumulates in the cells of the tiiyroid gland, where destruction of tiiyroid cells occurs without damaging other cells throughout the body. 

Half-lives span a very wide range (Table 17.5). Consider strontium-90, for which the half-life is 28 a. This nuclide is present in nuclear fallout, the fine dust that settles from clouds of airborne particles after the explosion of a nuclear bomb, and may also be present in the accidental release of radioactive materials into the air. Because it is chemically very similar to calcium, strontium may accompany that element through the environment and become incorporated into bones once there, it continues to emit radiation for many years. About 10 half-lives (for strontium-90, 280 a) must pass before the activity of a sample has fallen to 1/1000 of its initial value. Iodine-131, which was released in the accidental fire at the Chernobyl nuclear power plant, has a half-life of only 8.05 d, but it accumulates in the thyroid gland. Several cases of thyroid cancer have been linked to iodine-131 exposure from the accident. Plutonium-239 has a half-life of 24 ka (24000 years). Consequently, very long term storage facilities are required for plutonium waste, and land contaminated with plutonium cannot be inhabited again for thousands of years without expensive remediation efforts. 

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