Development of the thyroid gland of New-Zealand white rabbit [electronic resource].

Includes references.

The development of thyroid glands or New-Zealand rabbit8 Was studied hi 28 fetuses (10.30 days) and 28 rabbits (3 days-5years). The thyroid premordia appeared at the 12th day Of gestation as 2 masses or cords and clumps of cells. The gland assumed the bilobed form with a narrow Isthmus in between at the 18th day. Small primitive follicles with narrow empty lumina appeared in 14.day.o1d fetuses. True follicles were recorded in 20.22 days old fetuses while colloid was seen in the lumina of the central follicles at the 24'11 day. Light (C. or Parafollicular) cells were seen for the first time at the 12th . day. With development of the follicies, C. cells appeared between the follicular cell. and some of them come in contact with colloid. The ultimobranehial body (UBB) was observed in 20 days old fetusel close to the thyroid anlage and entered into its tissue at the 22nd day. Later on it gave thyroid..like follicles or ultimobranchial cysts. With the electron microscope (EM) follicular cells of early developing fetuses were not yet differentiated.. They contained few ill-developed rough endoplasmic reticulum (rER) and mitochondria. The organelles became. 'well developed and the cells started to secrete colloid in full term fetuses. The maximum rate of secretary activity was achieved in the glands of adult rabbits. Changes in the thyroid glands during the postnatal life up to S years of age (age of senility) were followed up and described.

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