树蛙结冰的选段

taidas03

Before winter comes, the frogs eat ravenously, storing a starch in their livers. During the winter, the frog saves a huge stockpile of carbohydrate in its liver as glycogen. It used this when it had to quickly raise its blood sugar levels for cryoprotection (staying alive while frozen). A freeze triggers their bodies to convert the starch into other compounds, most often glucose, or blood sugar or glycerol. The frogs become, in essence, diabetic. Ice crystals begin forming just beneath the frog's skin, when the temperature drops below 0°C and the normally pliant and slimy frog becomes slushy. Stimulated by the freezing temperature, starch, which is stored in the liver, is converted into glucose (blood sugar) or glycerol. If, after 3 hours, the temperature falls lower, ice races inward through the frog's arteries and veins. The glucose is distributed to the major organs and muscles, lowering the freezing temperature of the water inside the frog's cells.

After 24 hours, the glucose or glycerol prevents the water inside the frog's cells from freezing, but allows ice to form in spaces around the cells and in the cavities around the organs. Some of the glucose may be used as a fuel to generate energy in cells, while they are surrounded by cells and cut off from fuels that would otherwise be delivered by blood. The glucose lowers the freezing temperature of water inside the frogs' cells, so the cells stay liquid, even as ice fills the space around them. If the water inside the cells froze, the jagged ice crystals would destroy everything inside, killing the frog.
The organs can also use their own supply of glycogen (the polysaccharide carbohydrate reserve) for this purpose. The organs are surrounded by a mass of ice keeping them cool, without damaging them. This enables the frog to hibernate without any body functions, which require energy. When glucose or glycogen are fermented without oxygen, lactic acid accumulates as the end product in tissues and lactate builds up slowly in the organs while the frog is frozen. Carbohydrate fermentation fuels the low metabolic rate in frozen animals. Glucose tends to stay stable during the freeze.

The heart, lungs and brain stop working, while the eyes freeze to a ghostly white. The frog has no heartbeat, does not breathe and will not bleed if cut. Up to 65% of the body water may freeze, as the cells are protected by a natural antifreeze. The frog is very compact and solid to the touch and makes a small thud when dropped, but it is not dead and is unharmed by the process. The legs may be tucked in under the body, so there are no body parts sticking out and vulnerable to breaking off. One frog turned almost purple with its limbs and head stuck in contorted positions. The frog may survive being frozen from 2 weeks to perhaps 2-3 months, although the temperature under the snow may rise above freezing point at times.

XYXB

谢谢~

ssisi888

赞！原理来了！

moonwalker

thanks.

是背景介绍？

taidas03

青蛙为何结冰不死之原理

雪印

谢了

jennyzh

Thanks a lot

wudi0314

谢谢lz