T3 and T4 Relations to Thyroid Problems

The function of the thyroid gland is to take in iodine found in food and to convert it into thyroid hormones .The popular terms for two very important thyroid hormones, Thyroxine and Triiodothyronine are T4and T3 respectively.

Thyroid cells are the only cells in the body which can absorb iodine. The cells combine iodine and amino acid tyrosine to make T3 and T4.These are stored in the butterfly shaped thyroid gland that lies just below the voice box.T3 and T4 are then released into the blood stream and are transported throughout the body where they control metabolism (conversion of oxygen and calories to energy).

Thyroxine (T4) and Triiodothyronine (T3) are the hormones needed for normal brain development, especially during life's first three years. If enough thyroid hormone is not produced by the gland it may lead to mental retardation. It is also needed for normal growth and development in older children. Adults require the hormone to regulate the energy use of the body. T3 has a greater effect on the way the body uses energy than T4 even though T3 is present, normally, in smaller amounts.

When the level of thyroid hormones (T3 and T4) drops too low, the pituitary gland produces Thyroid Stimulating Hormone (TSH) which stimulates the thyroid gland to produce more hormones. Under the influence of TSH the thyroid will manufacture and secrete T3 and T4 thereby raising their blood levels. The pituitary senses this and responds by decreasing its TSH production.

You may wish to read more at: T3 and T4

Thyroxine (T4) in the blood is attached to a protein called the "Thyroxine Binding Globulin". Less than a percent of the T4 is unattached. Tissue function in the body is affected by free thyroxine; bound thyroxine does not affect. A "Total T4 Blood Test" is carried out to count both bound and free thyroxine.

T3 in the blood is also attached to the thyroxine binding globulin and like T4 less than a percent is unattached. A "T3 Blood Test" counts the attached and unattached triiodothyronine.

More answers to thyroid questions at: Thyroid Problems