Thyroid Hormones and Their Functions

Hormone used for replacement and suppression of thyroid function.

A synthetic thyroid hormone, more potent than T4, used in myxedema coma due to its rapid onset.

A combination of T4 and T3 (4:1 ratio) used for thyroid hormone replacement.

An autoimmune disorder causing hyperthyroidism due to abnormal thyroid receptors.

A drug used to treat hyperthyroidism by inhibiting thyroid hormone synthesis.

Thyroid hormones play a crucial role in our physical, mental, and sexual development. They influence key processes like oxygen consumption, metabolism, glucose utilization, and even heart function.

Thyroid hormones are synthesized and secreted through a series of steps involving the peroxidase enzyme. These steps include iodide uptake, organification of iodine, coupling of iodotyrosines, and storage and release of thyroid hormones.

Hypothyroidism indicates a deficiency of thyroid hormones. Treatment often involves supplementing with levothyroxine, a synthetic thyroid hormone.

Hyperthyroidism, also known as thyrotoxicosis, is characterized by excessive production of thyroid hormones. This leads to an accelerated metabolism in all body tissues, often affecting females more than males.

The thyroid gland uses a feedback mechanism to regulate the release of thyroid hormones. This mechanism involves the pituitary gland and the hypothalamus, ensuring a balanced level of thyroid hormones in the body.

Drugs like Propylthiouracil that inhibit the production of thyroid hormone by blocking the enzyme thyroid peroxidase. They are used to treat hyperthyroidism.

Orlistat, a weight-loss drug, can lead to hypothyroidism by interfering with thyroid hormone production. It inhibits the enzyme thyroid peroxidase, disrupting the process of creating thyroid hormone.

Alpha-lipoic acid might counter the effects of thyroid hormones by hindering the conversion of T4 to T3, the active form of the hormone. This could lead to decreased thyroid hormone activity.

Rifampin, an antibiotic, speeds up the metabolism of thyroid hormones. This reduces their effectiveness, requiring dosage adjustments for patients on thyroid hormone medications.

Thioamides are effective in managing mild cases of hyperthyroidism. They are also used before thyroid surgery to reduce hormone levels and before radioactive iodine therapy to enhance its effect.

Common side effects of Thioamides include low white blood cell count (leukocytopenia), enlarged thyroid gland, allergic reactions (rash, fever, liver and kidney problems) and joint pain.

Propylthiouracil, a thioamide, can interfere with vitamin K, increasing the risk of bleeding when taken with warfarin, an anticoagulant.

Propylthiouracil can amplify the levels of digoxin, a heart medication, potentially leading to irregular heartbeat. Reducing digoxin dosage is necessary when both medications are used simultaneously.