Questions and Answers
What is the normal range of TSH values in μIU/L?
What is a symptom of iodine toxicity?
What is a function of thyroxin?
What is a characteristic of goiter?
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What is a method of assessing iodine status?
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What is a consequence of chronic iodine deficiency?
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What is the primary consequence of iodine deficiency in adults?
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What is the primary function of thyroid hormones in fetal development?
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What is the primary function of zinc in the body?
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What is the process by which iodine is absorbed in the GI tract?
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What is a symptom of zinc deficiency?
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What is the primary consequence of iodine deficiency in neonates?
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What is the primary function of thyroxin hormone?
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What is the primary source of iodine in the diet?
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What is the consequence of ingesting more than 60 mg/kg of iodine?
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What is the mechanism by which iodine is transported into follicular cells?
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What is the RDA of selenium for pregnant women between 14-18 years old?
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What is the function of selenium in thyroid hormone metabolism?
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What is the deficiency disease associated with selenium deficiency in the cardiac system?
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What is the primary function of thioredoxin reductases, a type of selenoprotein?
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What is the common symptom of selenium toxicity?
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What is the function of selenium in reproduction?
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What is the source of selenium in the human body?
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What is the consequence of selenium deficiency on iodine deficiency?
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Study Notes
Iodine Toxicity
- Ingestions of more than 60 mg/kg can cause severe toxicity, leading to black and bloody stools, diarrhea, liver damage, metallic taste in the mouth, nausea, and vomiting blood.
Iodine Distribution and Functions
- Iodine is concentrated in the thyroid gland, with 15-20 mg of iodide available in the human body, 80% of which is in the thyroid gland and the rest in the blood.
- Iodine plays a crucial role in the formation of thyroid hormones, regulating growth and development, metabolic rate, and maintaining normal reproductive functions.
- Iodine is essential for intellectual development and the development of neurons in fetal life.
Digestion and Absorption of Iodine
- Dietary iodine is either bound to amino acids (AA) or in free form, existing as iodate (IO3) or iodide (I-).
- During digestion, iodate is reduced to iodide by glutathione, and iodide is rapidly absorbed in the gastrointestinal tract, including the stomach.
- A small amount of iodinated AA is absorbed, and free iodide enters the bloodstream.
Thyroid Hormone Synthesis
- Iodine trapping involves the uptake of iodine from capillaries to follicular cells in the thyroid gland through active transport, using an ATP-dependent Na-K pump.
- Thyroglobulin is synthesized in the rough endoplasmic reticulum (RER) of follicular cells, combining with CHO and moving to the Golgi apparatus.
- This is the substrate for thyroid hormone synthesis.
Thyroid Hormone Synthesis Cont…
- Oxygenation of iodide occurs when iodine is moved to the follicular lumen through an iodide/chloride transporter.
- Iodine is oxidized, and iodination of thyroxin takes place within thyroglobulin, catalyzed by thyroid peroxidase.
- Monoiodotyrosine is converted to diiodotyrosine, eventually forming thyroxin (T4), which can be stored in the thyroid gland for several months.
Thyroid Hormone Functions
- Thyroid hormones, including T3 and T4, circulate as free or bound forms, binding to globulin, albumin, and prealbumin.
- Thyroid hormones control metabolism, regulate growth, and have antioxidant functions.
Measuring Iodine Status
- Urinary iodine levels, rate of goiter prevalence, serum thyroid-stimulating hormone (TSH), and serum thyroglobulin are used to measure iodine status.
Iodine Deficiency
- Iodine deficiency in adults can lead to goiter, coughing, hypothyroidism, and myxedema (severe hypothyroidism), as well as changes to the voice, difficulty swallowing, and difficulty breathing.
- Iodine deficiency in the fetus can result in abortions, stillbirths, and cognitive abnormalities.
- In neonates, iodine deficiency can cause cretinism, characterized by severe mental defects, stunted growth, and low function of body organs.
Iodine Deficiency Symptoms
- Iodine deficiency symptoms include weight gain, fatigue, weakness, thinning hair, dry skin, feeling colder than usual, slowed heart rate, and learning and memory difficulties.
Food Sources of Iodine
- Seafoods, iodinated salt and salt-added foods, eggs, milk, and plant sources (dependent on iodine levels in soil) are good sources of iodine.
Excess Iodine Consumption
- Excess iodine consumption can cause iodine toxicity, which is rare and difficult to identify, leading to symptoms such as nausea, vomiting, diarrhea, and in severe cases, delirium, stupor, and mental state disturbances.
Assessment of Iodine Status
- Urinary iodine levels, rate of goiter prevalence, and serum thyroid-stimulating hormone (TSH) are used to assess iodine status.
Zinc Functions
- Zinc acts as a metalloenzyme, functioning as a cofactor in enzyme active sites, and is involved in the synthesis of insulin, maintenance of gut and skin health, DNA/RNA synthesis, energy metabolism, wound healing, immune function, taste receptor function, and fatty acid metabolism.
Food Sources of Zinc
- Beef, chicken, wholemeal flour, white flour, and oysters are good sources of zinc.
Zinc Deficiency
- Acute zinc deficiency can cause anorexia, cessation of growth, skin lesions, diarrhea, loss of appetite, birth defects, mental defects, hair loss, and abnormal taste and smell.
- Chronic zinc deficiency can lead to stunted growth, lack of sexual development, anemia, and other health problems.
Zinc Toxicity
- Zinc toxicity can occur at levels of 300 mg/d, 20 times the US RDA, leading to symptoms such as nausea, vomiting, cramps, and diarrhea.
Assessing Zinc Status
- Plasma levels, breast milk, and saliva can be used to assess zinc status.
Selenium Functions
- Selenium is a constituent of 25 selenoproteins, including thioredoxin reductases, glutathione peroxidases, and is involved in thyroid hormone metabolism, DNA synthesis, apoptosis, DNA repair, antioxidant functions, reproduction, and protection from infections.
Selenium Functions Cont…
- Selenium prevents lipid oxidation and platelet aggregation, and has antioxidant and anti-inflammatory activities, which can help prevent Alzheimer's disease.
RDAs for Selenium
- Recommended dietary allowances (RDAs) for selenium vary by age, with increasing levels recommended for pregnancy and lactation.
Food Sources of Selenium
- Drinking water, grains, meat, poultry, seafood, and eggs are good sources of selenium.
Selenium Deficiency
- Selenium deficiency can lead to Keshan disease (cardiac myopathy), osteoarthritis, and exacerbate iodine deficiency.
Selenium Toxicity
- Selenium toxicity can cause hair loss, nail brittleness or loss, skin rash, nausea, diarrhea, fatigue, irritability, and nervous system abnormalities.
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Description
This quiz covers the effects of ingesting excessive amounts of iodine, including severe toxicity and liver damage, as well as the absorption and distribution of iodine in the human body.
