Quiz 38: Pancreatic Hormones and Antidiabetic Drugs

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Thyroid hormones- triiodothyronine (T 3 ) and thyroxine (T 4 ) are secreted by thyroid gland play important roles in the growth and metabolism of tissues. Thyroid hormones are necessary for the development and differentiation of almost every cell type of the human body. Thyroid hormones also affect energetic pathways of cells by regulating protein, fat, carbohydrate and vitamin metabolism in the body. Thyroid hormones are necessary for other hormones to work properly. Thyroid hormones secreted by the thyroid gland enter the cell. In many cells, T 4 is converted into T 3 which is a more potent form. These hormones play important roles in metabolism. Thyroid hormones are also known as metabolic hormones because of their role in the body's basal metabolic rate. For example binding of T 3 and T 4 to intracellular receptors present on the mitochondria result in the production of ATP due to increased nutrient breakdown. T 3 and T 4 also influence the transcription of genes of glucose oxidation. During these processes, heat is produced as byproduct and body temperature raises (calorigenic effect). Thyroid hormones are also important for the proper development of fetuses and children due to their role in protein synthesis. Thyroid hormone plays important roles in cell building, repair and function by affecting protein synthesis, carbohydrate metabolism, and fat metabolism. They also play important roles in nervous system development of fetuses and children. Thyroid hormones can influence reproductive hormones, and therefore can influence libido and fertility. Thyroid hormones are essential for the functioning of growth hormone and catecholamines. They can increase the body's sensitivity to catecholamines. Increased levels of T 3 and T 4 result in increased heart rate and hypertension. Thyroid hormone plays important roles in protein, fat and carbohydrate metabolism. They are also important for growth and development and proper functioning of other important hormones.

Thyroid hormones- triiodothyronine (T 3 ) and thyroxine (T 4 ) are secreted by the thyroid gland and play important roles in the growth and metabolism of tissues. Thyroid hormones are necessary for the development and differentiation of almost every cell type of the human body. Thyroid hormones also affect energetic pathways of cells by regulating protein, fat, carbohydrate and vitamin metabolism in the body. Thyroid hormones are necessary for other hormones to work properly. Thyroid hormones are also important for the proper development of fetuses and children due to their role in protein synthesis. Thyroid hormone plays important roles in cell building, repair and function by affecting protein synthesis, carbohydrate metabolism, and fat metabolism. They also play important roles in nervous system development of fetuses and children. Thyroid hormones can influence reproductive hormones, and therefore can influence libido and fertility. a. Hypothyroidism is a condition in which thyroid gland does not produce enough thyroid hormone. Hypothyroidism can be caused by the destruction of thyroid gland either by exposure to radiation; iodine deficiency; pituitary dysfunction or by surgical removal of the thyroid gland. Hypothyroidism can lead to various metabolic changes. The total absence of T 3 and T 4 can result in myxedema characterized by round puffy face, dry skin, decreased blood pressure, bradycardia, intolerance to low temperature. Respiratory acidosis, electrolyte balance and coma may happen in severe cases. So this person might be suffering from myxedema. Hormone replacement therapy is the treatment of choice for this person. Hence this person is suffering from myxedema due to hypothyroidism and can be treated by hormone replacement therapy with T 3 and T 4. b. Severe hypothyroidism in infants can lead to cretinism. Cretinism occurs due to deficiency of iodine in mother during pregnancy or anatomic defect in the thyroid gland. Iodine is essential for the synthesis of thyroid hormones. Hypothyroidism in children can lead to the shorter height, delay in permanent teeth development, slowed mental development, brittle hair and intolerance to cold. This condition can be treated with hormone therapy (levothyroxine). Hence she is suffering from cretinism due to hypothyroidism and can be treated with hormone therapy (levothyroxine). c. Hypersecretion of thyroid hormones is called hyperthyroidism. Hyperthyroidism may be caused either by the tumors of thyroid, pituitary or hypothalamus or by autoimmune diseases. Symptoms of hyperthyroidism include heat production, tachycardia, muscle weakness, anxiety and weight loss. Hyperthyroidism can be treated with antithyroid drugs or radiation to reduce the size and vascularity of the tumor in glands before surgery. Other treatment options are thioamide drugs which inhibit the incorporation of iodide into tyrosine. Hence this person might be suffering from hyperthyroidism and can be treated by the antithyroid drug; radioactive iodine or thioamide drugs. d. When calcium concentration in the plasma becomes too high, it is called hypercalcemia. Hypercalcemia can occur due to tumours in the parathyroid gland, neoplasm, multiple myeloma and kidney dysfunction. Symptoms of hypercalcemia are nausea, vomiting, headache, arrhythmias and increased gastric acid secretion. Therefore, this woman might be suffering from hypercalcemia. Calcitonin and bisphosphonates are used in the treatment of hypercalcemia. Hence the woman is suffering from hypercalcemia and can be treated by the administration of calcitonin or bisphosphonates.

In this question, the patient has been diagnosed with hyperthyroidism. Her lab report says T 3 -T 4 level is elevated and TSH level is low, along with TRH. • T 3 (tri iodothyronine) and T 4 (thyroxine) are thyroid hormones secreted by the thyroid gland. The condition where there is an Increase in the secretion of T 3 and T 4 is called as hyperthyroidism. • The hypothalamus releases a hormone called TRH -Thyrotrpin-Releasing Hormone. TRH acts on the anterior pituitary gland and causes the release of the Thyroid Stimulating Hormone (TSH) into the blood. • This TSH activates the thyroid gland cells to secrete T 3 and T 4. • When the levels of T 3 and T 4 decreases below normal value, the pituitary gland will produce TSH and causes thyroid gland to produce more T 3 and T 4 and increase its blood level to normal. • When the level rise, signals reach the hypothalamus to reduce the TRH release and inturn the pituitary gland decreases its TSH production. • This is negative feedback mechanism. In the question, the TRH level is low. TRH is secreted by hypothalamus. Hence the problem in this hyperthyroid patient is not at the level of Hypothalamus. Hence option (A) is wrong answer. Since TRH produced by hypothalamus is low, it does not stimulate the anterior pituitary gland to secrete TSH. In the question TSH is low along with low TRH. Hence the problem is not at the level of Anterior pituitary gland. Hence option (B) is wrong answer. Parathyroid gland is a gland situated on the posterior surface of thyroid gland. They secrete the hormone parathormone. It is associated with the maintanence of blood calcium level in the body. Parathormone does not have a role in maintanence of thyroid hormones. Hence option (D) is wrong answer. The pituitary gland has two lobes: the anterior and the posterior. Posterior pituitary secretes two hormones. They do not play a role in causing hyperthyroidism. Hence the problem is not at the level of posterior pituitary. Hence option (E) is the wrong answer. Inspite of low TSH and TRH, if T 3 and T 4 increase, it indicates an overactive thyroid gland which is secreting too much thyroid hormone or hyperthyroidism. Hence the problem is at the level of thyroid gland. Hence option (C) is the correct answer.

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