1. osmoregulation 渗透调节 李征程
英文释义：osmoregulation controls the concentration of dissolved substances in the cells and body fluids of an animal
李征程

2. freshwater teleosts 2
elasmobranch
marine teleosts 1 3
osmoregulation

3. 1 ：osmoregulation in elasmobranch
elasmobranch fish like sharks and rays have a superb ability to maintain internal and external osmotic pressure balance. They contain a lot of urea(尿素) in their blood, so the concentration of liquid in the body is higher than that of seawater, forcing them to urinate（排尿） to remove excess water from the body.
If we have the chance to eat the shark,we will feel that there is a general pungent smell, the reason is that the shark's body contains urea. Urea can not only maintain the high osmotic pressure of the body fluids in the cartilage, reduce the infiltration of salt, but also can accelerate the effect of salt discharge.

4. To prevent osmotic stress in the hyperosmotic marine environment,marine elasmobranchs convert their nitrogen wastes into urea and retain high concentrations of it in their blood.

6. 2:osmoregulation in freshwater teleosts Freshwater teleosts are not the same as marine teleosts, and the salt concentrations of freshwater teleost bodies are higher than those of the outside water. That is to say, the salt concentration of fresh water is low, the proportion is low, the density is small, according to the principle of osmotic pressure, the external fresh water will continue to mass into the fish body, for this reason, the freshwater teleosts expel excess water from the body only through the kidneys.

7. Freshwater teleosts are hyperosmotic to their environment and therefore tend to gain water and lose solutes by diffusion across the thin menbranes of the gill .Solutes also are lost in the urine.If left unchecked,the fish's ceils would swell and burst from the constant influx of water.To prevent this,freshwater fishes excrete a large volume of dilute urine and actively transport solutes back into their blood.

9. 3:osmoregulation in marine teleosts The salt concentration of the marine teleost fish body is much lower than that in the seawater, because of the large amount of salt in seawater, the proportion is high and the density is large. According to the principle of osmotic pressure, the water power in the fish body tissue will continuously seep out from the gills and surface. In order to maintain water balance in the body, the sea fish will have to swallow a lot of seawater to make up the body's dehydration. However, due to large mouth to swallow seawater into the body, the salt also increased greatly, so that, in addition to removing part of the salt from the kidney, "secretion of chlorine cells" in the gill tissue complete the task of discharging salt.

10. Marine teleosts face the opposite problem from that of freshwater teleosts.
The high salt concentration of the ocean draws water out of the fish,and ions diffuse in across the permeable membranes .To counteract potential dehydration,marine teleosts drink sea water and actively excrete excess salts.

13. 淡水硬骨鱼:只通过肾脏，将过多的水分排出体外。
summary in chinese
淡水硬骨鱼:只通过肾脏，将过多的水分排出体外。
海水硬骨鱼:吞食大量海水，以弥补体内的失水。同时还要依靠肾脏，和鳃组织中的“泌氯细胞”来完成排盐任务
软骨鱼:通过血液内的高浓度尿素，一方面保持体液的高渗压抑制海水盐分进入身体，另一方面尿素还能起到加速盐分排出的作用。

14. For more information, please read the textbook 100 to 105 pages
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