Monocarboxylate Transporters


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Monocarboxylate Transporters

Monocarboxylate Transporters

Thyroxine (T4) and triiodothyronine (T3) are our major thyroid hormones. These hormones are best measured in their free forms, called free T4 (FT4) and free T3 (FT3). It’s long been presumed that thyroid hormone circulating within the plasma is readily available to react with our cells. Thyroid hormone must enter our cells before it can cause the effects it’s associated with. Normally, our thyroid hormone levels give a good idea of our thyroid status.

Normally, the pituitary gland regulates thyroid hormone levels by its secretion of thyroid-stimulating-hormone (TSH or thyrotropin). Normally, the pituitary secretes more TSH when thyroid hormone levels are low. TSH, in turn, orders thyroid cells to produce more thyroid hormone, helping prevent hypothyroidism.

Hypothyroid Symptoms, Normal Labs

High plasma levels of thyroid hormone cause hyperthyroidism, and low levels cause hypothyroidism. Normally, in hypothyroidism, TSH levels are elevated and in hyperthyroidism, TSH levels are low. However, plasma levels may not reflect what's happening at the cellular level.