ABSTRACT
Thyroid An understanding of the basic physiology of the thyroid and its control mechanisms is essential for correct interpretation of thyroid scans. Figure 2.1A shows how the thyroid produces T4, T3, and rT3, and how T4 controls its own production via a negative feedback system. The eventual levels of thyroid hormone in the blood are dependent on factors other than thyroid function alone. Figure 2.1B diagrammatically illustrates the uptake of Iodine (and radioiodine), incorporation into thyroid hormones into the blood under TSH stimulation.
