pronephron

== English == === Etymology === From pro- +‎ nephron. === Noun === pronephron (plural pronephrons) (biology) The first part of the urogenital system to be differentiated in a vertebrate embryo, which functions as a simple excretory organ in simpler forms, serves as a provisional kidney in some fish and amphibians, and only appears as a temporary embryonic structure in reptiles, birds, and mammals. ==== Synonyms ==== pronephros