Final answer:
Thyroid follicle cells remove thyroglobulin from the follicular cavity by endocytosis, which is stimulated by TSH. Enzymatic cleavage within the follicle cells then releases T3 and T4 into the bloodstream.
Step-by-step explanation:
Follicle cells in the thyroid gland remove thyroglobulin from the follicular cavity through a process known as endocytosis. When thyroid-stimulating hormone (TSH) binds to receptors on the follicular cells, endocytosis is stimulated, causing the absorption of thyroglobulin-laden colloid from the central cavity into the follicular cells.
Here, the thyroglobulin undergoes enzymatic cleavage by lysosomal enzymes, which liberates the thyroid hormones triiodothyronine (T3) and tetraiodothyronine (T4 or thyroxine). Once free, T3 and T4 diffuse through the follicular cell membrane and enter the bloodstream, where they will exert their physiological effects, such as increasing the rates of mitochondrial ATP production.