Semester 2 - Endocryn System - Thyroid Gland

Levothyroxine is the most appropriate drug for replacement therapy in a hypothyroid patient because it is a synthetic form of the thyroid hormone thyroxine (T4), which is deficient in hypothyroidism. It helps to restore the levels of thyroid hormone in the body, thereby improving symptoms and restoring normal metabolism. Propranolol, Triiodothyronine, Propylthiouracil, and Lithium are not used for replacement therapy in hypothyroidism.

Hashimoto's thyroiditis is an autoimmune disease where the body's immune system mistakenly attacks the thyroid gland. This leads to inflammation and damage to the thyroid tissue, eventually causing hypothyroidism. Autoimmune destruction is the most common cause of Hashimoto's thyroiditis, as it is primarily driven by the body's own immune response rather than external factors such as radiation, surgical removal of the thyroid, or hormonal imbalances like hypopituitarism. Polyglandular failure syndrome is a condition that involves the autoimmune destruction of multiple endocrine glands, including the thyroid, but it is less common compared to Hashimoto's thyroiditis as a standalone cause.

In a patient with a benign thyroid adenoma ("toxic nodule"), the adenoma itself is producing excess thyroid hormone (T4), leading to elevated levels of T4. However, the excess thyroid hormone suppresses the production of thyroid-stimulating hormone (TSH) from the pituitary gland, resulting in reduced levels of TSH. Therefore, the expected results in this patient would be T4 elevated and TSH reduced.

In the case of iodine deficiency, the thyroid gland is unable to produce sufficient amounts of thyroid hormone. This leads to a decrease in the levels of T4, as it is the primary hormone produced by the thyroid gland. However, the pituitary gland senses the low levels of T4 and tries to compensate by increasing the production of TSH (thyroid-stimulating hormone). Therefore, in a patient with iodine deficiency, the expected results would be T4 reduced and TSH elevated.

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In Grave's disease, enlargement of the thyroid gland is caused by an antibody that stimulates TSH receptors. This antibody binds to the TSH receptors on the thyroid gland, leading to an overproduction of thyroid hormones. This excessive stimulation of the thyroid gland results in the enlargement of the gland and the increased production of thyroid hormones, leading to the symptoms of Grave's disease such as hyperthyroidism.

A high dose of iodides inhibits thyroid hormone release from follicular cells. Iodides are known to interfere with the synthesis of thyroid hormones in the thyroid gland. High levels of iodides can block the uptake of iodine by the follicular cells, which is necessary for the production of thyroid hormones. This inhibition leads to a decrease in the release of thyroid hormones into the bloodstream.

The symptoms described in the question, such as lethargy, respiratory difficulties, hoarse cry, and poor sucking, are indicative of hypothyroidism in a newborn. The physical examination findings of large fontanelles, macroglossia, distended abdomen, cyanotic skin, hypotonia, slow reflexes, and hypothermia further support this diagnosis. Levothyroxine is the appropriate drug in this case as it is a synthetic form of thyroid hormone and can effectively treat hypothyroidism.

After being treated with radioactive iodine, the patient's TSH levels are elevated. This suggests that the radioactive iodine treatment successfully reduced the thyroid hormone levels, leading to an increase in TSH production by the pituitary gland. To normalize the thyroid hormone levels, the patient would most likely be prescribed levothyroxine, a synthetic form of thyroid hormone. Levothyroxine would help replace the deficient thyroid hormone and restore normal thyroid function.

The patient's elevated TSH levels and presence of thyroid peroxidase antibodies indicate that she has hypothyroidism, specifically Hashimoto's thyroiditis. Levothyroxine is the appropriate drug for this patient as it is a synthetic form of thyroid hormone that can replace the deficient hormone in the body and help regulate the thyroid function. Potassium iodide is used to treat hyperthyroidism, Propranolol is a beta-blocker that can help manage symptoms of hyperthyroidism, Methimazole is used to treat hyperthyroidism, Loperamide is an anti-diarrheal medication, and Diltiazem is a calcium channel blocker used to treat hypertension and angina.

Propylthiouracil is an antithyroid medication used to treat hyperthyroidism. Agranulocytosis is a serious toxicity that can occur in patients taking propylthiouracil, although it is rare. Agranulocytosis is a condition characterized by a severe decrease in the number of white blood cells, specifically granulocytes, which are important for fighting off infections. This can lead to a compromised immune system and an increased risk of developing serious infections. Therefore, it is important to monitor patients taking propylthiouracil for signs of agranulocytosis, such as fever, sore throat, or signs of infection, and discontinue the medication if necessary.

Propylthiouracil is the correct answer because it is an antithyroid drug that inhibits the enzyme responsible for the conversion of T4 to T3 in the liver. By blocking this conversion, propylthiouracil helps to reduce the levels of the active thyroid hormone, T3, in the body. This drug is commonly used in the treatment of hyperthyroidism to help control the overproduction of thyroid hormones.

The patient's symptoms, such as tiredness, feeling cold, weight gain, muscle cramps, dry skin, and enlarged thyroid gland, are consistent with hypothyroidism. The blood test results confirm this, as the patient has elevated TSH levels and slightly below normal T3 and T4 levels. Thyroxine is the main hormone produced by the thyroid gland, and administering it can help replace the deficient thyroid hormones and alleviate the symptoms of hypothyroidism. Therefore, the administration of thyroxine is the most likely treatment option for this patient.

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The levels of both T3 and T4 are low in this patient, indicating a deficiency in the proteins that bind to and transport these thyroid hormones. The most likely protein to be deficient in this case is thyroxin-binding globulin (TBG), as it is responsible for binding and transporting the majority of T4 in the blood. The normal TSH levels and normal size of the thyroid gland suggest that the issue lies with the binding and transport of thyroid hormones rather than with the production or secretion of thyroid hormones.

During pregnancy, the demand for thyroid hormones increases, and the woman's levothyroxine dose may need to be increased to maintain adequate thyroid hormone levels. This is necessary for the normal development of the fetus and to control the symptoms of hypothyroidism. Therefore, increasing the levothyroxine dose is the appropriate modification in therapy in this case.

The correct answer is that thyroid follicular cells secrete T4 hormone. This is characteristic of the thyroid gland because the thyroid follicular cells are responsible for producing and secreting thyroid hormones, including T4 (thyroxine). T4 is an important hormone that regulates metabolism and growth in the body. The other statements in the options are incorrect or do not accurately describe the characteristics of the thyroid gland.

Thyroid follicles do not include Para follicular cells that release calcitonin into the colloid. Calcitonin is actually produced by C cells, which are located outside of the follicles in the thyroid gland. The other statements are true. Thyroid follicles contain thyroglobulin, they are lined by epithelial cells that vary in appearance with the activity of the gland, they are surrounded by a fenestrated capillary network, and they are stimulated by TSH.

Thyroid peroxidase is an enzyme that plays a crucial role in thyroid hormone synthesis. It catalyzes the coupling of two molecules of DIT (diiodotyrosine) to form T4 (thyroxine), which is the main form of thyroid hormone produced by the thyroid gland. This process occurs within the thyroglobulin molecule, a protein that serves as a precursor for thyroid hormone synthesis. The correct statement correctly identifies the role of thyroid peroxidase in the synthesis of T4.

Iodine is necessary for the production of thyroid hormones. In cases of iodine deficiency, the thyroid gland is unable to produce enough thyroid hormones, leading to a decrease in negative feedback to the pituitary gland. This results in an increase in the secretion of thyroid-stimulating hormone (TSH) from the pituitary gland. Elevated TSH levels stimulate the thyroid gland to grow and enlarge, causing a goiter. Therefore, the enlargement of the thyroid gland in chronically iodine-deficient patients is most directly related to the elevated TSH level.

THIS QUESTION DID NOT HAVE AN ANSWER "E", BUT THE ANSWER KEY SAYS THE ANSWER IS "E".