What is the mechanism by which potassium iodide prevents radioactive iodine absorption?

Potassium iodide is effective in preventing the absorption of radioactive iodine by saturating the thyroid gland with non-radioactive iodine. When potassium iodide is administered, it rapidly elevates the levels of stable iodine in the body. The thyroid gland can only absorb a certain amount of iodine, and when it is saturated with stable iodine, it effectively blocks the uptake of any additional iodine, including radioactive isotopes. This mechanism is crucial in situations like nuclear accidents, where radioactive iodine may be released into the environment.

While options related to thyroid hyperactivity, iodine metabolism, or increased blood flow to the thyroid could theoretically impact thyroid function or iodine utilization, they do not play a direct role in the protective mechanism of potassium iodide against radioactive iodine. The saturation of the thyroid with stable iodine is the primary and most effective way potassium iodide achieves its protective effect, which is why this option is the correct choice.