T-4, T-3, T3 uptake and TSH
Thyroid-stimulating hormone (TSH) from the anterior pituitary, stimulates the production of thyroxin, and triiodothyronine, therefore, having a dramatic effect on the T4/T3 test results.
Thyrotrophs makeup 5% of the anterior pituitary and produce between 100-400mU/day of TSH.
Circadian peaks with the onset of sleep are between 9 pm-5am and a minimum between 4-7pm.
TSH is regulated by an open feedback loop via thyroxin whereby thyroxin passes into the CSF of the lateral ventricles and is taken up by the epithelial cells of the choroid plexus, which when thyroxin levels are low, stimulates TRH-secreting neurons in the hypothalamus.
TSH does the following:
1. Stimulates phospholipid metabolism
2. Stimulates purine and pyrimidine precursors and their incorporation into nucleic acids.
T-4 and 3 indicate the denitrification power of iodine via thyroxin with T3 being much more powerful than T4. All food contains active biological nutrients that are bound with nitrogen. When this food reaches the liver, the iodine is used to cleave the nitrogen from the nutrient.
Therefore, thyroxin and T3 are important in fat and protein digestion, absorption, and growth and endocrine function.
This catabolic activity begins once aerobic bound substances become totally anaerobic and lose the need for nitrogen bonding. Nitrogen is cleaved by T3 or T4 in the liver for example as in glycogen storage. Other substances are needed by specific cells and are transported via total binding globulin to the cells where at that point, the nitrogen bonds are cleaved.
Less than 1% of T3 is unbound. A high T-3 uptake indicates a hypothyroid, where a low T-3 uptake indicates a hyperthyroid.