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Abstract
Abstract
At 5 mm CVRL stage, the pronephros was in the form of a simple epithelial tubules which were fused with each other forming a wide tube. It was surrounded by an undifferentiated mesenchymal investment. The pronephros was completely missing at 13 mm CVRL stage and substituted by a connective tissue strand, the mesonephric ligament and the caudal extension of the pronephric duct persisted as mesonephric duct. The mesonephros was firstly seen at 5 mm CVRL stage, its size has reached its peak at 35 mm CVRL followed by gradual apoptotic regression of both glomerular and tubular elements. The primitive metanephros was firstly seen at 13 mm CVRL stage. It was composed of a centrally located epithelial ureteric bud and peripheral circumscribed masses of undifferentiated mesenchymal cells. The first morphological evidence of metanephric glomerulogenesis was observed at 28 mm CVRL stage in the basophilic, subcapsular, nephrogenic zone. The developing renal corpuscles were appeared at CVRL 35 mm CVRL stage. During 60 mm CVRL stage, the renal pelvis became more prominent. The pelvic branching gave rise to the future collecting ducts which extended towards the cortical zone. The differentiation of the renal tubules into proximal and distal convoluted tubules was observed at 95 mm CVRL stage .At 130 mm CVRL stage, the medulla was clearly delineated into medullary pyramids which in association cortical caps form the morphological basis for the advanced renal lobar formation. A gradual nephrogenic decline was noticed from the 940 mm CVRL on, however, the process of nephrogenesis was persisting throughout all the studied fetal stages.