小中大这个还用说嘛,尿素是小分子化合物,可以自由通过细胞膜,当然就可以进入肠道了。
==============================================================================================================
严格地说,“自由通过”有点过了,事实上----Gastrointestinal urea transporters are thought to play a significant role in the urea nitrogen salvaging process that occurs between mammalian hosts and their gut bacteria.
实际上,水,proton这类小分子都有通道,膜上有尿素通道应该不难接受。