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| typically found in ionic form I-, dietary iodine bound to amino acid/free as IO3- or I-, in enterocyte all is I- |
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| water, seafood, meat and vegetable content varies with soil content, through food processing in bread production & dairy industry in cleaners for milking equipment |
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| recommended method of distribution of iodine, 50+ yrs in US, Canada, & Switzerland where iodine deficiency and goiter were once common |
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| rapidly absorbed, ~100% absorbed, takes place in stomach and small intestine, iodate (IO3-) used in supplementation b/c high bioavailability |
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rapidly take up by thyroid(uptake varies with iodine intake) or kidney
T4 & T3 associated with 3 transport proteins: thyroxine binding globulin, albumin, transthretin |
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| primarily excreted in urine(~80-90%), low fecal excretion, kidneys have no mechanism to conserve iodine |
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| 15-20 mg(adequate) to <20mcg(deficiency) total body, thyroid contains 3/4 total body iodine |
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Definition
| blood iodide conc. cleared rapidly by thyroid from plasma, thyroid controls blood iodide conc. |
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Definition
| single function is synthesis of thyroxine and triiodothyronine |
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| Thyroid Hormone synthesis 1-3 |
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Definition
1: thyroid cells trap iodide by Na/K ATPase pump & oxidize iodide to iodine
2: iodine binds to tyrosyl residues of thyroglobulin, forms Thg-MIT, hydrogen peroxide accepts electron
3: Thg-MIT iodenates to Thg-DIT, then 2 Thg-DIT condense to Thg-T4 or DIT and MIT condense to Thg-T3 or Thg-rT3 |
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| Thyroid Hormone synthesis 4-5 |
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Definition
4: Thg-MIT & Thg-DIT if not used for thyroid hormone synthesis are deiodenated to make Thg
5: iodothyroglbulins are endocyted into thyroid cells, lysomal proteases hydrolyze & release thyroid hormones |
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Term
| Iodine conversion of forms |
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Definition
| several tissues deiodenate T4 to T3 & rT3, Selenium required for 5'-deiodinase |
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Term
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Definition
| urinary iodide, thyroxine(T4), thyroid stimulating hormone |
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regulates prenatal growth, & postnatal growth in stature and bone maturation
Deficiency: decreased BMR, macronutrient metabolism impaired, brain/muscle/skeletal developmental abnormalities, lung maturation abnormalities |
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very common b/c most soils around world are very low in I (particularly high mountains & frequent flooding areas)
Effects: prenatal mental retardation, delayed growth, slowness of movement, delayed reflexes, elevated blood lipids, cardiac insufficiency |
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| compensatory response to iodine deficiency, decreases plasma iodide & hormone synthesis, increases TSH release which increases thyroid cell size and number (causes enlarged thyroid gland) |
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Definition
| tracheal & esophageal pressure, may damage laryngeal nerves, respiratory difficulty, hoarseness |
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| iodine supplement, thyroidectomy |
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| most severe form of iodine deficiency, primary feature is severe mental retardation, 2 types: early & late pregnancy deficiency |
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| Early pregnancy cretinism |
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Definition
| inner ear & brain affected, mental retardation, short stature, spasticity of legs, deaf mutism, goiter |
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| short stature, mental retardation, hypothyroidism, (spasticity of legs, deaf mutism, & goiter ususally absent) |
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| causes ~4% of goiter, present in foods, it blocks iodine uptake & utilization by thyroid, casava directly associated |
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| Deficiency caused by Selenium |
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Definition
| Se in glutathione peroxidase, GP degrades peroxide and protects thyroid from oxidative environment needed for thyroid hormone synthesis, Se deficiency causes glutathione peroxidase & T4 deiodinase deficiency |
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Definition
RDA: 150mcg/d adults, 220mcg/d pregnant, 290 mcg/d lactating
UL: 1100mcg/d |
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