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Publicatie Laka-bibliotheek:
Molecular, cellular, biological characterization of childhood thyroid cancer. EUR 16538 EN (1996)

AuteurEuropean Commission
Datum1996
Classificatie 2.34.8.11/20 (TSJERNOBYL - ONGELUK & OMGEVING - MEDISCH/MUTATIES)
Voorkant

Uit de publicatie:

II BACKGROUND

II.1 Thyroid physiology

The main function of the thyroid is to produce the two iodide containing thyroid 
hormones T3 and T4. As iodide is found in small quantities in the environment and 
its levels may fluctuate widely, special mechanisms have evolved to sequester iodide 
taken in the drinking water and diet and to concentrate the element within the gland.
 The thyroid is composed of spherical structures (follicles) lined by epithelial cells 
(the follicular cells). The centre of these follicles contains a viscous material called 
colloid which acts as a final production site and reservoir for the two hormones. 
Thyroid hormone synthesis is a complex process which can be influenced by a great 
number of factors, including the level of available iodide itself. Briefly, iodide is 
actively taken up into the follicular cells, transported to the luminal border and bound 
to tyrosyl residues on the complex thyroid specific protein thyroglobulin to form 
monoiodotyrosine (MIT) and diiodotyrosine (DIT). These then undergo conjugation 
to form the two hormones tri-iodothyronine (T3) and tetraiodothyronine (T4). The 
latter two stages occur at the junction of the follicular cell and the colloid and are 
catalysed by another thyroid specific protein, thyroid peroxidase. Thyroglobulin 
containing the thyroid hormones is then stored in the colloid prior to reabsorption by 
the follicular cell. Lysosomes then fuse with the colloid droplets within the cell to 
allow degradation of thyroglobulin and release of MIT, DIT, T3 and T4. MIT and 
DIT are deiodinated by a thyroid specific deiodinase and the iodide released is 
recirculated for hormonogenesis. T3 and T4 are released into the circulation, where 
T3 is the more active hormone, but further deiodination takes place peripherally to 
release more T3 from T4 in target organs.

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