Kidney of accumulation

Japanese: 蓄積腎 - ちくせきじん（英語表記）kidney of accumulation

In embryos in the eggshell, hibernating animals, or animals that cannot use much water for excretion, waste products, especially nitrogenous metabolic products, cannot be excreted from the body, so they are converted into insoluble substances, removed from the metabolic system, and accumulated and stored; the organ involved in this is called the storage kidney. It is not necessarily an organ specialized in excretion, and in many cases it is performed as a secondary function of various organs, tissues, or cells. In reptile and bird embryos, nitrogenous metabolic products are converted into non-toxic, insoluble uric acid crystals and accumulated in the allantois, which remain in the eggshell when the animal hatches.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

卵殻中の胚や冬眠中の動物または排出に多くの水を使えない動物では，老廃物，特に窒素代謝産物を体外に排出することができないので，それらを不溶性の物質とし，体内の代謝系から除き蓄積･貯蔵するが，これにかかわる器官を蓄積腎と呼んでいる。必ずしも排出を専門にする器官とはいえず，各種の器官や組織あるいは細胞の副次的機能として行われている場合も多い。　爬虫類や鳥類の胚では窒素代謝産物を無毒で不溶性の尿酸結晶とし尿膜中に蓄積し孵化（ふか）のとき卵殻内に残す。

出典　株式会社平凡社世界大百科事典第２版について　情報

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