The bear is a typical hibernating animal. For bears, a year is mainly divided into three seasons: spring to autumn is the season of enjoyment; autumn to winter is the season for eating and special eating; winter solstice and spring is the sleeping season, because this period extends throughout the winter, so it is also called This is the “hibernation period.”
Xiong: I don’t need to urinate and urinate in hibernation, can you?
During the hibernation of bears, their metabolism will slow down and their body temperature will drop to 1°C to 9°C. All bodily functions are greatly reduced: breathing becomes weaker, heartbeat slows down, and sensitivity to external stimuli decreases. In addition, there is a very important feature, that is, during this time, they do not need to urinate.
Urinary and defecate can excrete nitrogenous compounds. Nitrogen-containing compounds cannot be discharged normally, and the non-protein nitrogen content in the bear’s blood will rise sharply. But strangely, this does not damage the bear’s kidneys or liver. You know, if the non-protein nitrogen content in human blood exceeds the normal value, a series of health problems will occur. The normal nitrogen content of blood in the human body is 0.2mg/ml～0.25mg/ml (whole blood), of which urea contains the most nitrogen. If it exceeds this value, it may indicate that your kidneys may have a problem. The determination of the non-protein nitrogen content in the blood is an important indicator for clinical judgment of renal function. When the kidney function fails, the non-protein nitrogen compounds in the blood will increase. This is also one of the reasons why humans cannot hibernate, because the metabolic rate is too slow, which will lead to excessive accumulation of harmful substances in the body.
Xiong: I am fat and healthy, can you do it?
The bear also has a magical ability. Before the start of hibernation, they will eat a lot of special food, eating into a big fat man. The Katmai National Park and Nature Reserve in Alaska even held a “Fat Bear Week” event for bears to see which bear eats the most. Netizens all over the world can vote. The 2019 champion is Holly No. 435, which is a “sister paper” (female).
If humans want to hibernate, they have to eat and drink to accumulate fat. But if people want to be such a fat man, something big will happen. Because if human body weight increases significantly, the sensitivity of fat, liver and muscle tissue cells to insulin will decrease, and insulin levels will increase. The increase in insulin will in turn prevent the breakdown of fat cells, thus forming a vicious circle and eventually developing insulin resistance. High insulin and high sugar content in plasma caused by insulin resistance often leads to metabolic syndrome, gout and type 2 diabetes.
At this point, bears really make people “envious, jealous, and hate”. Scientists have observed the blood sugar levels, insulin levels, weight, and other metabolic indicators of bears before, during and after hibernation. It was found that after they gained more than 45kg, their cells were still very sensitive to insulin, and their blood sugar and insulin levels remained stable. Although the bear will experience a temporary, seasonal period of insulin resistance after the start of hibernation, when spring comes, everything will return to normal.
So every spring, bears waking up from hibernation will not have health problems due to hibernation. Although they will be a little groggy when they first wake up, they are generally healthy. Simply put, although they are fat people in the early and middle stages of hibernation, they are healthy fat people. After the bear wakes up from hibernation in the spring, the body’s fat is almost consumed, but it just looks thinner, and the muscle content is basically unchanged. After a lot of eating and drinking, it can return to its normal posture.
However, if a person lies in bed for too long, the problem of muscle atrophy will occur. If a person has been lying still, muscle mass will decrease at a rate of 10% to 15% per week. Of course, this reduction will not last forever, and it will stop until after the energy intake of one day is “balanced”.
Why is there no problem with bears hibernating for so long?
A group of researchers from Washington State University in the United States published a research report in the journal Communication Biology in September 2019, explaining what happens to the cells of grizzly bears in hibernation.
Studies have found that hibernation has different effects on the cells of each tissue. Among them, the difference in gene expression in adipose tissue of bears is greatest during hibernation, while muscle tissue is almost unchanged. They also found that even in the fat cells of the same bear, most of the genes in the fat cells change their expression levels at different times of the year. In other words, if we want to obtain a bear-like hibernation ability through gene editing, it is also very difficult. Because this can’t be done by modifying one or two genes.
It is these genes that during bear hibernation, the expression of genes related to insulin signaling, muscle protein degradation, and urea production decreases, while the expression of genes related to muscle protein synthesis increases. This also explains why grizzly bears can keep the liver and kidneys healthy during hibernation, and their muscles can’t shrink.
In the future, humans may need “hibernation”, such as interstellar travel, but at this stage, it is still difficult to perfectly control the metabolism of human cells and maintain a relatively healthy level.