海产软骨鱼类 通过血液中多量的尿素保持较高的渗透压，从食 物获得盐分。鳃和皮肤吸水。肾脏排尿和直肠腺分泌 可排除过多的盐分。 body fluids ca.1100 mOsm/kg medium ca.1000 mOsm/kg gills block loss of most urea and TMAO urea and TMAO retained by kidney divalent ions excreted in urine water absorbed ingests salts by gills(and skin) with food salts lost sodium excreted via feces by rectal gland FIGURE 13-2. Diagram summarizing osmoregulation of saltwater elasmobranch. 13 13 海产软骨鱼类 通过血液中多量的尿素保持较高的渗透压，从食 物获得盐分。鳃和皮肤吸水。肾脏排尿和直肠腺分泌 可排除过多的盐分