develops_from mesonephros A kidney formed of nephric tubules arising in the middle region of the nephric ridge; a transient embryonic stage that replaces the pronephros, but is itself replaced by the adult metanephros [in mammals; in fishes and amphibians it is the adult kidney]. [Evolution, Fourth_Edition_(2006)_McGraw-Hill, Function, Kardong_KV, Vertebrates:_Comparative_Anatomy, p.745][VHOG] AAO:0010384 As the pronephros regresses, the archinephric duct induces the sequential differentiation of tubules in the more caudal parts of the nephric ridge. (...) Tubules that differentiate in the middle part of the nephric ridge form a kidney called the mesonephros. This kidney functions in the embryos and larvae of all vertebrates. (...) In all vertebrate embryos, the kidney begins with the differentiation of a few renal tubules from the anterior end of the nephric ridge overlying the pericardial cavity. (...) This early-developing embryonic kidney is called the pronephros.[well established][VHOG] BTO:0001542 By contrast to the pronephros, the histological features of the mammalian mesonephros, with its primitive glomeruli, suggest that it probably functions as a primitive kidney, and is involved in the production of much of the amniotic fluid. Within the two mesonephroi, one located on either side of the dorsal mesentery of the hindgut, a substantial number (in the region of about 40 or more) of cranio-caudally segmented mesonephric tubules are formed. It has, however, been suggested that only the most rostrally located 4-6 pairs of mesonephric tubules drain into the mesonephric portion of the nephric duct. This is now seen to extend along the length of the mesonephroi, being located towards their lateral sides. The mesonephros is also retained over a considerably longer period than the pronephros, but gradually undergoes regression in a cranio-caudal direction. While the rostral part displays clear evidence of regression its more caudal part appears to display evidence of functional activity. Within the medial part of the mesonephros, vesicles are formed, although no glomeruli are formed there in this species. It is, however, difficult to believe that the relatively enormous mesonephroi do not have an excretory role in the mouse, only serving as a base for gonadal differentiation. In the human embryo, the medial part of the mesonephric tubules enlarges, become invaginated by capillaries, and form glomeruli. These then take on an excretory role. In the mouse, the mesonephric ducts appear to be patent throughout their length[GUDMAP, modified] CALOHA:TS-0624 EFO:0000928 EHDAA2:0001130 EHDAA:1581 EHDAA:5903 EMAPA:16744 EMAPA:27644 FMA:72171 GAID:1308 In mammals, the mesonephros is the second of the three embryonic kidneys to be established and exists only transiently. In fish and amphibians, the mesonephros will form the mature kidney MESH:D001755 Organ that is the definitive adult kidney. It replaces the earlier pronephros, which degenerates as the mesonephros becomes functional in feeding stage tadpoles.[AAO] TAO:0000529 The second stage of the kidney. It serves as the main excretory organ of aquatic vertebrates and as a temporary embryonic kidney in higher vertebrates. It is composed of the mesonephric duct (also called the Wolffian duct), mesonephric tubules, and associated capillary tufts. A single tubule and its associated capillary tuft is called a mesonephric excretory unit; these units are similar in structure and function to nephrons of the adult kidney. The mesonephros is derived from intermediate mesoderm in the vertebrate embryo. UBERON:0000080 UMLS:C0025492 VHOG:0000038 Wolffian body XAO:0000141 ZFA:0000529 amphibian adult kidney corpus Wolffi mesonephric mesonephric kidney mesonephroi middle kidney opisthonephros opisto nephros opistonephros uberon kidney pronephros mesoderm-derived structure