With regard to the human body, there is also a strange saying of “resigning the old and welcoming the new”: in 7 to 10 years, you can get a brand new body.
Thinking about it, it seems really reasonable. From the skin peeling off, dandruff “flying” in the air can be seen, in the human life, the human body will generate a large number of new cells to replace the dead or damaged old cells, the old cells will disappear or leave the body in the form of shedding. Then, when new cells completely replace old cells, we can get a new body.
But, is this the truth? Let’s first look at how new cells replace old cells.
How to replace the old and new?
To understand how new cells replace old cells, you first need to understand how new cells are formed.
The human body mainly produces new cells in two ways. The first is that the existing cells undergo a fairly simple division process, the original cells split into two new cells, which are essentially replicas of the original cells; the second way is specific to stem cells. These special stem cells, although spread throughout the body, are few in number, as we know the most well-known hematopoietic stem cells, which are distributed in the bone marrow and rarely present in the blood. Stem cells not only replicate to create new stem cells, but also create new “specialized” cells, such as red blood cells and neuronal cells, which are cells with special functions.
In order to make room for new cells, old cells must die. The most common form of death in old cells is programmed death, a DNA-controlled, active and orderly way of dying. During death, DNA indicates that the cell synthesizes a series of special “scissors” enzymes that “cut” mitochondria, cell membranes, and other cellular components; cell components are “cut” and necrosis occurs, in which the cell membrane loses control of moisture in and out. The ability to cause the cells to dehydrate or swell; eventually the cells shrink or break and die. Cell debris after death is generally eaten by macrophages or neighboring cells, so as not to affect the normal function of other cells, and the surface of the human body will fall off.
This kind of programmed death is very necessary for living things. For example, in the development of human embryos, the fingers that are initially differentiated are connected. Under the action of programmed cell death, the cells of the tissue between the fingers die, the tissues disappear, and the fingers are separated. In the case of a frog, the tail cell also undergoes programmed death, causing the tail to fall off.
The first new cells continue to function after replacing the dead old cells. After a while, the second batch of new cells is formed, and the first batch of new cells are replaced by a second batch of new cells, which are repeated… From this point of view, the cells have a certain life span.
Some people may think this way: “Since cells always die, there will always be a day when new cells will completely replace old cells. Can you get a new body at that time?” In fact, they ignored the most important point: Different kinds of cells have different life spans, and some cells will even accompany you for the rest of your life and will not be replaced.
Different cells, different life spans
Cells are the basic building blocks of the human body and come in about 200 different types. Each cell has a different function and therefore a different life span. In general, the lifespan of cells depends on how much work they need to do. Just like a car, because the use and wear of the tire is obviously more than the transmission during the driving process, so the frequency of changing the tire is always higher than the frequency of changing the transmission. Some parts of the human body that are used frequently and wear more are also It needs to be updated earlier and faster than other parts to maintain the body’s function.
For example, some cells arranged on the surface of the gastrointestinal surface are usually replaced once every five days due to continuous erosion by corrosive substances such as stomach acid; the skin is the outermost layer of the body and will be subject to a certain degree of wear, in order to maintain optimal condition. The epidermal cells of the skin are replaced every two to three weeks; the red blood cells in the blood need to transport oxygen to all tissues of the body, and the life span is only about 4 months; in comparison, the use rate of fat cells is lower than other cells. Therefore, its life span is quite long, averaging about 10 years.
There are also some cells that have been replaced by human life, such as many neuronal cells, which are very different from other cells. The work of neuronal cells is to receive and process signals from other neuronal cells, and then pass the processed signals to the next neuronal cell or nerve center, which means that the neuronal cells are not arranged one after another like other cells. In the human body, they are “connected” and connected to each other to form a complex neural network, so that the “interlocking” neural network is also the basis of brain work. If the neuron cells can be replaced, you must first disconnect the “ring” so that the signal is not transmitted during the disconnection period, when the brain will not work, you can never let your brain stop working for a while, then let the new Replace the old neuron cells with neuron cells! After all, for people, the brain stops working and most of the time means death. Therefore, the vast majority of neuronal cells can not be replaced, when the brain is injured, neuronal cell damage or death, the impact will be permanent, such as Alzheimer’s disease can not cure.
Therefore, even if the cells are replaced, you will never be a brand new one. When it comes to certain cells, you will be entangled with them for life.