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urogenital system[¦yu̇r·ə¦jen·əd·əl ‚sis·təm]
the aggregation of anatomically and functionally related organs of excretion and reproduction in animals and man.
Invertebrates. The interconnection of excretory and reproductive organs is achieved in various ways in the invertebrates. In acanthocephalans and priapulids, the excretory organs are called protonephridia; these open into the ducts of the gonads. In most polychaetes, in echiurids, and in sipunculids and brachiopods, the gonaducts retain their basic function but fuse with the excretory organs, which thus take on the additional function of transporting the reproductive products. In certain polychaetes, the excretory organs are called metanephridia; these structures serve to transport reproductive products, while the primary gonaducts, called coelomoducts, partially perform an excretory function. In many mollusks, the sole function of the primary gonaducts is to excrete waste products; the secondary ducts of the gonads serve to transport the reproductive products.
Vertebrates. Ova and sperm pass through the ducts of the excretory organs in all vertebrates, including humans. In female animals and in women, the ova are conveyed through the oviducts, which derive from the müllerian duct. In most male fish and in all amphibians, reproductive products are transported through the Wolffian duct, which is usually the ureter as well. In male reptiles, birds, mammals, and men, the primitive kidney, or mesonephros, is transformed into the epididymis and serves to secrete semen; the Wolffian duct is transformed into the deferent duct. The secondary kidney, or metanephros, together with the ureter, which extends from the metanephros, are the essential constituents of the excretory system in amniotes and humans.
REFERENCESDogel’, V. A. Sravnitel’naia anatomiia bespozvonochnykh, part 1. Leningrad, 1938.
Beklemishev, V. N. Osnovy sravnitel’noi anatomii bespozvonochnykh, 3rd ed., vol. 2. Moscow, 1964.
Shmal’gauzen, I. I. Osnovy sravnitel’noi anatomii pozvonochnykh zhivotnykh, 4th ed. Moscow, 1947.
A. V. IVANOV