Physiological Anatomy of the Thyroid Gland

A small, central portion of the thyroid gland, measuring approximately 2 cm in length.

Tiny, closed sacs that make up the thyroid gland. They are filled with colloid and lined by cuboidal epithelial cells.

A protein-rich fluid found inside the thyroid follicles. It contains thyroglobulin, the precursor to thyroid hormones.

A large glycoprotein present in colloid. It serves as the building block for the thyroid hormones.

Specialized cells within the thyroid gland that produce and secrete calcitonin, a hormone regulating calcium levels in the blood.

A hormone produced by C cells that helps regulate calcium levels in the blood by decreasing them when they are too high.

An enzyme essential for thyroid hormone production. It catalyzes the attachment of iodine to thyroglobulin, forming the thyroid hormone precursors.

A state of insufficient thyroid hormone production, commonly affecting women. It disrupts the normal function of the body's metabolism.

A complex regulatory system involving the hypothalamus, pituitary gland, and thyroid gland. It controls the production and release of thyroid hormones.

A hormone secreted by the hypothalamus that stimulates the pituitary gland to release TSH.

The most common cause of hyperthyroidism, accounting for 60-80% of cases.

A life-threatening condition that involves having severely low levels of white blood cells, specifically neutrophils, which are needed to fight infections. This is a serious complication of some medications used to treat hyperthyroidism.

A class of medications that block the action of adrenaline, helping to relieve symptoms of hyperthyroidism like palpitations, anxiety, and tremors. They can be used alone or in combination with other medications.

A medication that blocks the conversion of thyroxine (T4) to triiodothyronine (T3) in both the thyroid and peripheral tissues. This is beneficial in hyperthyroidism as it reduces the amount of the more potent thyroid hormone, T3.

A medication that inhibits thyroid peroxidase (TPO), the enzyme responsible for attaching iodine to thyroglobulin, thereby reducing the production of T3 and T4. It is another option for treating hyperthyroidism.

A hormone that is four times more potent than T4. It plays a significant role in regulating metabolism and can be used to treat hypothyroidism.

The inactive form of thyroid hormone. It is converted to T3 in the body and is used to treat hypothyroidism, as it is more readily available in oral form.

A medication used to treat hypothyroidism. It is a synthetic form of thyroid hormone that is readily absorbed and available in various dosages.

A condition that can lead to a decreased need for thyroid hormone, requiring adjustments in medication dosages.

The thyroid hormone axis is regulated by a complex feedback loop involving the hypothalamus, pituitary gland, and thyroid gland. Elevated thyroid hormone levels signal the hypothalamus and pituitary to decrease TRH and TSH production, respectively, resulting in decreased thyroid hormone synthesis and release. This negative feedback loop maintains homeostasis by preventing excessive thyroid hormone levels.

Primary hypothyroidism occurs when the thyroid gland itself is unable to produce enough thyroid hormone. This can be caused by autoimmune diseases, iodine deficiency, or damage to the thyroid gland from surgery or radiation therapy. In primary hypothyroidism, the body attempts to compensate by increasing TSH production, but it is unable to overcome the underlying problem.

Hashimoto's thyroiditis is an autoimmune disorder in which the body's immune system mistakenly attacks the thyroid gland, leading to its destruction and a decline in thyroid hormone production. It is the most common cause of hypothyroidism in the United States.

Secondary hypothyroidism occurs when the pituitary gland fails to produce enough TSH. This can be caused by pituitary tumors, trauma to the pituitary gland, or other conditions affecting the pituitary gland. In secondary hypothyroidism, TSH levels are low, which leads to decreased thyroid hormone production.

Levothyroxine (Synthroid) is the drug of choice for treating hypothyroidism. It is a synthetic form of T4, the main thyroid hormone. Levothyroxine is typically taken orally and effectively replaces the thyroid hormone that the body is unable to produce.

The dosage of levothyroxine is adjusted based on individual needs and TSH levels. It's essential to take levothyroxine on an empty stomach, preferably in the morning, for optimal absorption. The dosage is usually titrated until TSH levels normalize. Regular monitoring of TSH levels is crucial to ensure proper treatment and avoid over or under-replacement.

Patients taking levothyroxine should avoid consuming foods and supplements that may impair absorption, such as iron, calcium, and multivitamins containing these minerals. These substances can interfere with the absorption of levothyroxine, reducing its effectiveness.

Thyroxine (T4) is the main thyroid hormone produced by the thyroid gland. It has a long half-life of about 7 days, making it a stable and long-acting hormone. T4 is absorbed from the intestine with an efficiency of about 80% when taken orally.