Thyroid Physiology 1

A single layer of cuboidal epithelial cells that line the thyroid follicles and are responsible for the synthesis and secretion of thyroid hormones.

The protein that serves as the backbone for thyroid hormone synthesis, containing several tyrosine residues where iodine can attach.

The fluid that fills the thyroid follicle, where thyroglobulin is stored and thyroid hormone synthesis takes place.

A crucial mineral that gets converted to iodide and used in the synthesis of thyroid hormones.

A transporter protein responsible for taking iodide from the bloodstream into thyroid follicular cells.

An enzyme that plays a vital role in thyroid hormone synthesis, catalyzing the attachment of iodine to tyrosine residues in thyroglobulin.

A hormone secreted by the hypothalamus that triggers the release of thyroid stimulating hormone (TSH) from the anterior pituitary gland.

A hormone secreted by the anterior pituitary gland that stimulates the thyroid gland to produce and release thyroid hormones (T3 and T4).

A negative feedback loop where thyroid hormones (T3 and T4) inhibit the release of TSH and TRH, preventing excessive hormone production.

The process by which the thyroid gland synthesizes T3 and T4, involving the conjugation of tyrosine and iodine within thyroglobulin.

The thyroid gland actively takes up iodide from the bloodstream using a transporter protein called the sodium-iodide symporter (NIS).

Thyroid peroxidase (TPO) oxidizes iodide ions (I-) into iodine (I2), which is then transported into the colloid of the thyroid follicle.

The oxidized iodine (I2) is added to tyrosine residues within thyroglobulin, creating mono-iodotyrosine (MIT) and di-iodotyrosine (DIT).

Two iodinated tyrosine residues (MIT or DIT) are coupled together by TPO to form the thyroid hormones tri-iodothyronine (T3) and thyroxine (T4).

Thyroglobulin (TG), a large protein, is made in the follicular cells and secreted into the colloid of the thyroid follicle. It serves as a storage and transport molecule for thyroid hormones.

Pendrin is a transporter protein that actively transports chloride ions (Cl-) into the colloid. It is important for maintaining the electrochemical balance of the thyroid follicle.

Thyroid stimulating hormone (TSH) is a hormone produced by the pituitary gland. It regulates all steps of thyroid hormone synthesis and secretion.

The activity of the Na-Iodide Symporter (NIS) is regulated by TSH. Higher TSH levels increase NIS activity, leading to greater iodide uptake by the thyroid.

TPO is a crucial enzyme responsible for both iodide oxidation and coupling of iodinated tyrosine residues. It plays a central role in thyroid hormone synthesis.

T3 and T4 are released into the blood when TG containing the thyroid hormones is taken back into the follicular cells and broken down. They then circulate throughout the body, controlling important bodily functions.