**2.4. Pseudofollicles**

Some of the main problems involved in thyroid physiology *in vitro* studies are the loss of follicle architecture, thyrocyte polarity and T3 and T4 hormone synthesis [54]. As mentioned above, the follicle lumen disappears in the monolayer with its colloid and the thyrocyte membrane domain polarity necessary for carrying out hormone synthesis [55,56]. However, tridimensional structures can be induced by covering monolayers with ECM elements, they become re-organised into two- to four-cell structures around the intercellular cavity in the presence of TSH, called pseudofollicles by some authors and "follicles" by others [54,56,57,58,59,60,61,62]. These pseudofollicles are unstable, short-duration structures and do not reproduced *in vitro* the function of iodide incorporation in Tg or synthesis of T3 or T4, and shown that follicle structures' thyrocyte polarity is necessary for studying thyroid physiology and the molecular processes implicated in such function [63].
