Functions of thyroid hormones fetal development

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Functions of Thyroid Hormones • Fetal development, particularly neural and skeletal systems • Control metabolic rate of all cells • Promote sufficient pituitary secretion of growth hormone and gonadotropins • Regulate protein, carbohydrate, and fat metabolism • Exert chronotropic and inotropic cardiac effects • Increase red blood cell production • Affect respiratory rate and drive • Increase bone formation and decrease bone resorption of calcium • Act as insulin antagonists Thyroid hormone production involves a series of steps. Dietary intake of protein and iodine is needed to produce thyroid hormones. Iodine is absorbed from the intestinal tract as iodide. The thyroid gland withdraws iodide from the blood and concentrates it. After iodide is in the thyroid, it enters into a series of reactions to form T 4 and T 3 . These hormones bind to thyroglobulin and are stored in the follicular cells of the thyroid gland. With stimulation, T 4 and T 3 break off from thyroglobulin and are released into the blood. They enter many cells, bind to the nucleus, and turn on genes important in metabolism. Thus the presence of T 4 and T 3 directly regulates basal metabolic rate (BMR).
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Calcium and phosphorus balance occurs through the actions of calcitonin This hormone also is produced in the thyroid gland. Calcitonin lowers serum calcium and serum phosphorus levels by reducing bone resorption (breakdown). Its actions are opposite of parathyroid hormone. The serum calcium level determines calcitonin secretion. Low serum calcium levels inhibit the release of calcitonin. Elevated serum calcium levels increase its secretion. Other factors that increase calcitonin release are pregnancy, a high-calcium diet, and an increased secretion of gastrin. Parathyroid Glands The parathyroid glands consist of four small glands located close to or within the backsurface of the thyroid gland They regulate calcium and phosphorus metabolism by acting on bone, kidney, and the intestinal tract Bone is the main storage site of calcium. PTH increases bone resorption (bone release of calcium into the blood from bone storage sites), thus increasing serum calcium. In the kidneys, PTH activates vitamin D, which then increases the absorption of calcium and phosphorus from the intestines. In the kidney tubules, PTH allows calcium to be reabsorbed and put back into the blood. Serum calcium level is the major controlling factor of PTH secretion. Secretion decreases when serum calcium levels are high, and it increases when serum calcium levels are low
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Use a systems approach to obtain the history of patients with a possible endocrine problem. This approach can be difficult because of the variety and combination of clinical manifestations.
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