**3. Description of the different regulatory factors synthesized by C cells and their potential effects on thyroid hormone synthesis**

The most important objective of the current review is to present new evidence of the paracrine regulation exerted by C cells upon follicular cells, through the secretion of numerous factors synthesized by C cells in the immediate vecinity of the follicular epithelium, which could act in a synergistic or antagonist manner. To accomplish that objective, we will expose the functional role played by the most studied C-cell secreted factors on the activity of follicular cells mediated through their specific receptors.
