Kilpnäärmefolliikuliteks

Kilpnäärmefolliikuliteks are the fundamental structural and functional units of the thyroid gland. These spherical or ovoid structures are lined by a single layer of follicular cells, also known as thyrocytes. The space within each follicle, called the follicular lumen, is filled with a gelatinous substance called colloid. The colloid is primarily composed of thyroglobulin, a large glycoprotein synthesized by the follicular cells. Thyroglobulin serves as a precursor for the thyroid hormones, thyroxine (T4) and triiodothyronine (T3).

The follicular cells play a crucial role in the synthesis, storage, and secretion of thyroid hormones. They actively take up iodine from the bloodstream, which is then incorporated into tyrosine residues of thyroglobulin within the follicular lumen. This process is known as iodination. Subsequently, the follicular cells reabsorb thyroglobulin from the colloid and, under the stimulation of thyroid-stimulating hormone (TSH) from the pituitary gland, proteolytically cleave it to release T4 and T3 into the circulation.

The size and appearance of the thyroid follicles can vary depending on the functional state of the thyroid gland. In a metabolically active state, follicles tend to be smaller with less colloid, and the follicular cells may appear more cuboidal or even columnar. Conversely, in a state of reduced activity, follicles are typically larger and distended with colloid, and the follicular cells appear flatter or squamous. The intricate structure of kilpnäärmefolliikuliteks is essential for maintaining normal thyroid hormone levels, which regulate metabolism, growth, and development throughout the body.