Which of These Events Does NOT Happen During Thyroid Hormone

Question

Which of these events does NOT happen during thyroid hormone secretion
A)The follicular cells phagocytize a piece of colloid.
B)T₄ and T₃ are subsequently diffused out of the cell into the blood.
C)T₄ and T₃ are secreted by exocytosis of the colloid that has been internalized by the follicular cells.
D)A greater amount of T₄ is secreted than T₃.

Accepted Answer

Phagocytosis of a piece of colloid does not happen during thyroid hormone secretion. Instead, the follicular cells internalize colloid by pinocytosis, and the enzymes in lysosomes break down the thyroglobulin to release T₄ and T₃. T₄ and T₃ are then secreted into the blood via diffusion or exocytosis. The ratio of T₄ to T₃ secretion is approximately 20:1.