Thyroid gland – Historical aspects, Embryology, Anatomy and Physiology.

Thyroid gland is an important endocrine organ. Its hormone thyroxine is essential for life. The structure and function of thyroid gland were discovered during 17th to 20th centuries. Thyroid surgery is being done since early 19th century, perfected by Theodre Kocher in early 20th century . Thyroid is the first endocrine gland to develop in embryo and is endodermal origin. The surgically important anatomical relations of thyroid are recurrent laryngeal nerve, parathyroid glands and external laryngeal nerve with variations. Thyroid gland secrets thyroxine hormone which contains Iodine. Thyroxine has effects on all organs of body and its secretion is regulated by Pituitary. Present article throws light on some historical aspects, embryology, anatomy and physiology of thyroid gland based on relevant articles and textbooks.

Multi-nodular goiter: Epidemiology, Etiology, Pathogenesis and Pathology.

Multi-nodular goiter is a common endocrine disorder worldwide. It is endemic in certain populations. It is more common in women and presents mainly in 4th and 5th decades of life. Various factors have been implicated for the development of multi-nodulor goiter, most common being Iodine deficiency. Nodular goiter results from uni or multifocal hyperplasia of follicular cells which may have autonomy of growth and autonomy of function. The process can be divided into five stages which result in the classic appearance and histology of multi-nodulor goiter. Present article deals with epidemiology, etiology, pathogenesis and pathology of multi-nodulor goiter based on relevant articles searched on pubmed.

Estudio morfolóiico del cultivo a largo plazo d folículos aislados y cerrados de tiroides de cerdo / Morphological Study of Long-term culture of closed isolated pig folicles

La unidad morfológica y funcional de la glándula tiroides es el folículo, estructura ovoide cerrada, constituida por una capa de células cúbicas (tirocitos) que encierran un lumen lleno del coloide secretado por ellas. En cultivo, tanto la estructura como la función del folículo se pierden rápidamente en las primeras 24 horas. Sin embargo, si se cultivan folículos cerrados de tiroides de rata conservan la arquitectura folicular, la morfología del tirocito y la función hasta la síntesis de hormonas tiroides de manera similar a la glándula in vivo. En este trabajo describimos el aislamiento y cultivo de folículos porcinos cerrados y su análisis morfológico. Los folículos se aíslan por digestión enzimática y disociación mecánica del parénquima tiroideo, luego se cultivan sobre agarosa con y sin hormona tirotrópica o tirotropina (1 mU/ml, TSH). El tejido de tiroides porcino obtenido tiene las mismas características de una glándula hipotiroidea in vivo, un epitelio casi plano, retículo endoplásmico rugoso (RER) exiguo, complejo de Golgi (CG), y microvellosidades escasas y cortas. Los folículos cultivados sin TSH conservan la forma ovoide y el coloide en su interior, y la misma ultra-estructura del tejido in vivo, RER y CG muy escasos, pero con el tiempo de cultivo aumenta la longitud de la microvellosidades y el espesor del epitelio. En presencia de TSH el epitelio se hipertrofia desde el primer día y las cavidades foliculares se reducen considerablemente. Se demuestra que folículos cerrados de tiroides durante ocho días (d) de cultivo conservan su morfología con y sin TSH. Además, estos responden al estímulo de TSH disminuyendo su cavidad folicular y aumentando el espesor del epitelio folicular.

The morphological and functional unit of the thyroid gland is the follicle - an ovoid closed-structure, constituted by a layer of cubical cells (thyrocytes) that lock up a full lumen of the colloid secreted by themselves. In culture, the structures as well as the function of the follicles are lost rapidly in the first 24 hours. However, if the rat thyroid follicles closed are seeded since the beginning of the culture, these conserve the follicular structure, the thyrocyte morphology and the function even as the thyroid hormone synthesis in a similar way to the gland in vivo. This work describes the isolation and the culture of closed swine thyroid follicles and its morphological analysis. The follicles are isolated by enzymatic and mechanic digestion of the thyroid, then they are cultured in agarose with and without thyrotropin (1 mU/ml, TSH). The swine thyroid tissue obtained has the same characteristics of an in vivo hypothyroid gland, an almost flat epithelium, low quantity of Rough Endoplasmic Reticulum (RER) and Golgi complex (GC), short and very scarce microvillus. The isolated and closed follicles cultivated without TSH preserve the ovoid form and the colloid in the lumen, and the same ultrastructure of the thyroid tissue in vivo, RER and GC, but the length of the microvillus as well as the thickness of the epithelium were increased with the culture time. In the presence of TSH the thickness of the epithelium increases from the first day and the follicular cavities reduce considerably. The isolated and closed follicles preserve their morphology in the long term (8 days) of culture with and without the TSH. Besides, they responded to the stimulus of the TSH reducing the follicular cavity.

Distribution of the Basement Membrane Components in the Rat Thyroid Gland during the pre - and postnatal Period / 대한해부학회지

It is well known that the spatial patterns of basement membrane[BM] components show a close correlation with the morphogenetic process in developing organs during pre- and postnatal period. But little is known about the chronological changes in BM components during the development of thyroid gland. To investigate the correlation of the distribution of BM components with the development of the thyroid gland, immunohistochemical localization of the BM components was performed, using rat fetuses[from 15 to 21 days of gestation] and pups[from 1 to 14 days]. According to the histological features with H.E. staining, prenatal development[El5-21] of the rat thyroid could be divided into 3 representative stages : 1] Undifferentiated primordium of thyroid epithelia, forming cell cords or cell nests [until El5 day]. 2] An intervening stage of cell proliferation with the pattern of lobulation[El6-17 days]. 3] Stage of maturing follicles[El8-21 days]. It could be concluded that differentiation of the thyroid follicle are terminated during the prenatal period and growth in size and number occurs during the first two weeks after birth. By the immunohistochemical localization of laminin[LM], fibronectin[FN], type IV collagen[CIV], the basement membranes investing thyroid follicles could be clearly delineated at 15 days of gestation. Reactivity for LN and CIV associated with BM increased with advancing development, while that of FH was apparently weakened during the 2 weeks after birth. On the other hand immunoreactivity for CIV in the same age group increased, compared to that of previous swage of development. These results indicate that BM components were expressed in distinct spatial patterns with advancing development of thyroid gland. Based on these observations, it could be concluded that these BM components are important determinants in epithelial growth and differentiation during thyroid development.