Structure of rat ultimobranchial bodies after birth

Abstract

The evolution of ultimobranchial bodies in Holtzman rats during the first 64 weeks after birth was studied by reconstructing three-dimensional models from serial sections stained by the periodic acid-Schiff technique.Radio-autography with 125I was made to see if ultimobranchial cells and/or follicular cells lining the lumen of mixed follicles were able to iodinate proteins. The term ultimobranchial body designates herein an embryonic vesicular structure (derived from the third pharyngeal pouch) whose wall is made of stratified squamous epithelium. During the first week after birth, the vesicular ultimobranchial body elongates rapidly and becomes a canal or a duct. During the second week, cell desquamation brings about local dilatations in the lumen of these ducts; with further enlargement ultimobranchial follicles will appear. In one-day-old rats, mixed follicles are present. Only the follicular component of mixed follicles iodinates proteins as is shown by radioautography. The reconstructed models enlarge rapidly up to the 56th day after birth at which time their weight has increased nineteenfold. These same models show that the three morphological components of ultimobranchial parenchyma, namely ducts, follicles and mixed follicles, are in continuity within the thyroid parenchyma. The formation of new thyroid follicles after birth and the possiblility that the ultimobranchial parenchyma may function as an endocrine gland of holocrine type are discussed.

Fine Structure of the Second Kind of Thyroid Follicles in Mature Guinea Pigs

“…They might represent a transi tional cell between the S-follicle cell and the thyroid follicle cell. Transformation of cells in the second type of follicle has earlier been reported as Calvert [1975] in rats has observed cells which seem to be transitional forms between young thyroid follicle cells and basal U cells. As already stated, the lat ter cell type seems to correspond to the dark fibrillar cells found in the present study.…”

“…This cell can clearly be distinguished from the S-follicle cell by means of its con tents of numerous widely dilated cisternae of rough-surfaced endoplasmic reticulum dispersed throughout the cytoplasm, and by absence of hemi-desmosomes and pinocytose vesicles in the basal part. As no secre tory granules and very few colloid-contain ing vacuoles are seen, these cells display an ultrastructure which is characteristic for a hypoactive thyroid follicle cell [Ekholm, 1964], In a previous paper [Juhl, 1981] it was suggested that the distended follicle may be regarded as a kind of mixed follicle [e.g., Calvert, 1975] as cells with a morphology and an enzymatic activity similar to those of thyroid follicle cells were observed in this part of the follicle at the light microscopic level. The finding of cells with an ultrastruc ture corresponding to that of thyroid follicle cells in the present study strongly supports this suggestion.…”

Cellular Integration of Thyrocytes and Thyroid Folliculogenesis: A Perspective for Thyroid Tissue Regeneration and Engineering.

“…One now has two hypotheses at hand about the mechanism of formation of a thyroid follicle lumen. The first is that a follicle lumen originates from intercellular spaces [83][84][85], and the second sees it deriving from intracytoplasmic cavities [86][87][88]. In a 3-D collagen gel culture system, intracytoplasmic cavities appear in thyrocytes.…”

Thyroid Calcitonin Cells and Unusual Follicles in the Fox

“…The ultimobranchial cysts (unusual folli cles) are defined as being a large, elongated, tubular structure enveloped by a connective tissue capsule [Jordan et al, 1973;Calvert, 1975], After a survey of the existing litera ture, it appears that the final fate of the UBB in mammals (including man) is not clear. Kingsbury [1939] and Van Dyke [1941] observed that UBB usually under goes degeneration in mammals disappearing entirely or resulting in the formation of epithelial cysts within the pharyngeal derivatives.…”

“…Politzer [1936] and Norris [1937] believed that the UBB converts into thyroid parenchyma. It has been reported that in the guinea pig [Klapper, 1946], mouse [ Wetzel and Wollman, 1969] and rat Wollman and Neve, 1971;Krupp, 1972;Calvert, 1975] the UBB gives rise to ultimobranchial cysts. Cordier et al [1976] believed that these cysts in dwarf mice are the endodermal remnants of the UBB after the migration of parafollicular cells.…”