RESUMO
The thyroid gland and its hormones are so essential for normal growth and develodopment. The thyroid gland is unique in having a histological organization that provides for extracellular storage of its products in lumen of the follicles. Nowadays, laser is widely used in medical therapy. Laser beams are most effective as biological stimulants. Low energy laser irradiation produces various effects at the biochemical, cellular, histological and functional levels. So, this study aimed at studying the histological and ultrastructural effects of laser irradiation on the thyroid gland. In the present work 20 adult male albino rat were used. These animals were divided into two groups, control and experimental, each of them was formed of 10 animals. Each experimental animal was exposed to spot laser irradiation over the right lobe of the thyroid gland. The laser beam was applied for 5 minutes once daily for one month in a dose of 1.92 J/cm 2. The thyroid gland was fixed in either 10% formaldehyde solution for paraffin sections or in 5% gluteralehyde for semithin and ultrathin sections and routinely processed. The paraffin sections were stained with Hematoxeline and Eosin and Van Gisson stains. Whowever, semithin sections were stained with toluidine blue. Ultrathin sections were stained with uranyl acetate and lead citrate. The results showed that: The thyroid follicles were larger in size in experimental group than that of control group, more widely separated by thickened interacinar reticular septa. Heights of their follicular cells were variable from cuboidal in engorged thyroid acini, to columnar in less distended acini. Their colloid secretion was not homogeneously distributed among different follicles and even inside the same acinus. There was an increased vascularily in the form of perifollicular distended and tortuous blood vessels. Also, interacinar capillaries appeared more winded, engorged by blood cells and had thicker walls. By electron microscopy: apical surface of follicular cells was devoid of indentations and microvilli, in reverse to the control group. The cytoplasm was paler and contained lesser amounts of cytoplasmic organelles specially rough endoplasmic reticulum and its cisternae, mitochondria, lysosomes and large secretory granules but not free ribosomes. In conclusion, laser irradiation increases blood supply and does some cellular changes