Cells in the body are constantly renewing themselves, why do people still age?

Every 7 years, most cells in the human body are renewed - from the eyelashes to the esophagus. In other words, after about 7 years of cell replication, the human body is a majority of new cells, inside and out.

However, not all cells renew at the same rate and lifespan.

Olaf Bergmann, principal investigator at the department of cell and molecular biology at Karolinska Institutet in Stockholm, Sweden, told Live Science: "Most skin and gut cells are replaced very quickly, possibly within a few days. months. Cells in the liver regenerate at a slightly slower rate."

Blood cells in the human body.

Bergmann and his colleagues analyzed liver tissue using radiocarbon dating and found that most liver cells were replaced within 3 years.

There are cells in other organs and systems that regenerate even more slowly and lag behind 7 years.

For example, in the human heart cells renew at a rather slow rate. Only about 40% of the total number of cardiomyocytes (the cells responsible for the force of contraction in the heart) are changed during life.

Whereas it takes about 10 years for bone cells to regenerate an entire skeleton.

With the brain, the process of cell renewal can be even more "leisure". Scientists have found evidence that some neurons in the hippocampus (complex brain structures deep in the temporal lobes) renew, but only at an annual rate of 1.75%. But other types of neurons will stay with a person throughout their life, Bergmann said.

On the other hand, not all cells have the same lifespan. For example, cells in the stomach can renew as quickly as every two days, because they are constantly exposed to digestive acids.

The cells that make up the skin are replaced every two to three weeks. As the main defense against the environment, skin needs to be in top condition.

Whereas red blood cells last for about four months. White blood cells, a key player in fighting infection, can last from a few days to more than a week. In contrast, fat cells live quite a long time - the average age is 10 years.

If human organs such as skin, intestines and liver, are renewed every few years, then why don't people stay young forever?

"Even if a person's cells are relatively young, their biological age reflects how their body responds to time," explains Bergmann.

When organs renew cells, organs remain aged due to changes in the cells that regenerate. As cells multiply, DNA must constantly divide and copy. Over time, a cell's mutations can build up and affect its lifespan.

To put it more simply, even when the cells in all parts of the body are renewed, the DNA in the cells has aged from being copied so much that one feels the weight of all the years that have passed. pass.