Lesson 33: Thyroid and Parathyroid

Tri-iodothyronine (T3) and Thyroxine (T4) are synthesized in the thyroid follicle. T3 is more active than T4.

The process by which the body regulates thyroid hormone production, involving the hypothalamus, pituitary gland, and thyroid gland.

Thyrotropin-releasing hormone (TRH) is released by the hypothalamus and stimulates the pituitary gland.

Thyroid-stimulating hormone (TSH) is released by the pituitary gland and stimulates the thyroid gland to produce T3 and T4.

The liver and muscles convert T4 into T3, the more active form of the hormone.

When T3 and T4 levels are adequate, they signal the hypothalamus and pituitary to reduce TRH and TSH production, maintaining hormonal balance.

Hypothyroidism is characterized by low levels of T3 and T4, leading to impaired growth, development, and decreased metabolic activity.

T3 enters the target cell, binds to thyroid hormone receptors (TR), and activates gene transcription leading to increased protein synthesis for growth, development, and heat production.

A condition caused by high levels of thyroid hormones in the blood, leading to increased metabolism, and hyperactivity of organs like the nervous and cardiovascular systems.

A type of goiter (enlarged thyroid gland) that occurs due to insufficient iodine intake, but the thyroid gland functions normally.

A condition where the thyroid gland produces insufficient thyroid hormones, leading to slowed metabolism and various symptoms like lethargy, weight gain, and cold intolerance.

A condition where the thyroid gland produces excessive thyroid hormones due to excessive TSH (thyroid-stimulating hormone) secretion, usually caused by a pituitary adenoma.

A condition where the thyroid gland produces excessive thyroid hormones due to antibodies stimulating the TSH receptors on thyroid cells, leading to hyperthyroidism.

The most common cause of hyperthyroidism, characterized by overproduction of thyroid hormones, thyroid enlargement, and protruding eyes (exophthalmos).

A type of swelling that does not indent when pressure is applied, often associated with long-standing untreated hypothyroidism.

Protruding eyes, a characteristic symptom associated with Graves' disease.

Medication used for hyperthyroidism, targeting the thyroid gland. Examples include carbimazole and propylthiouracil.

A procedure to remove part or all of the thyroid gland to treat hyperthyroidism.

The primary treatment for hypothyroidism, a synthetic form of thyroid hormone (T4) that is taken orally.

A form of thyroid hormone (T3) that is sometimes used in situations of severe hypothyroidism, administered intravenously.

A drug that interferes with the production of thyroid hormones, used in the treatment of hyperthyroidism. It contains a sulfur-containing (thiocarbamide) group that is essential for its antithyroid activity.

A specialized type of treatment for hyperthyroidism using radioactive iodine, which selectively destroys thyroid cells.

Radioactive iodine (RAI) is a treatment for hyperthyroidism and thyroid cancer. It's a first-line treatment for hyperthyroidism. It is also used in combination with other treatments, such as surgery, radiotherapy, and tyrosine kinase inhibitor chemotherapeutics for thyroid cancer.

RAI is a specific type of radiation that targets the thyroid gland. It works by releasing beta radiation, which destroys thyroid follicle cells.

A common side effect of RAI treatment is hypothyroidism, where the thyroid becomes underactive. This is easily managed by replacing thyroid hormones with T4.

RAI treatment is absolutely contraindicated in pregnant women because it can damage the fetal thyroid tissue.

Beta-blockers are medications used to manage the symptoms of hyperthyroidism, like a fast heartbeat, tremors, and anxiety. They're also used during the preparation for surgery and while waiting for other treatments to take effect.

Thioureylenes, like carbimazole and propylthiouracil, reduce the production of thyroid hormones by interfering with the synthesis of thyroid hormones within the thyroid gland. They block the enzyme thyroid peroxidase, which is essential for the iodination of tyrosine residues in thyroglobulin, a precursor protein for thyroid hormones.

While thioureylenes can lead to a complete resolution of Graves' disease (remission), they can also be used as a temporary bridge before more permanent treatment options like surgery or radioactive iodine therapy are pursued.

Potassium iodide is a form of iodine that can be orally administered to inhibit the release of thyroid hormones from the thyroid gland. Its effects are temporary, lasting only a few weeks.

Potassium iodide is used to prepare patients with hyperthyroidism for surgery (to reduce their hormone levels) or for severe cases of hyperthyroidism (thyroid storm) by quickly lowering hormone levels and preventing further complications.

Potassium iodide can also be used to protect the thyroid gland from absorbing radioactive iodine (like iodine-131). This is essential in cases of nuclear accidents or emergencies, as it significantly reduces the risk of thyroid cancer and other radiation-induced thyroid conditions.

Thyroid storm is an acute, life-threatening condition triggered by an uncontrolled surge in thyroid hormone levels. It leads to a hypermetabolic state, putting stress on various organs and affecting their functions. Although previously common during thyroid surgery, improved preoperative management with potassium iodide has significantly reduced its occurrence.

Common side effects of thioureylenes include mild and reversible leukopenia, skin rashes, headaches, nausea, jaundice, and joint pain. However, rarer and more serious side effects such as neutropenia and agranulocytosis can occur, primarily during the first three months of treatment.

Both thioureylenes (carbimazole and propylthiouracil) and potassium iodide can cross the placenta, potentially affecting the fetal thyroid gland. These drugs are used with caution in pregnancy.