How often are the cells of our body renewed?

How old are you? Whatever your age, it is not of most of the structures that make up your body. Some do not even have hours of existence and only a few have been with him since he was born. Their tissues or organs, as well as the cells that form them, have very different ages from each other. The vast majority of cells are renewed and so do the tissues of which they are ashlars.

The most ephemeral cells are those that line the inside of the small intestine. The intestinal epithelium is a very active tissue, which is responsible for absorbing and digesting countless small molecules. Your cells are renewed every two to four days. In the digestive system there are others of very short life: those of the crypts of the colon are renewed every three or four days, those of the stomach between every two and nine, and Paneth cells of the small intestine -between whose functions is the defense against intestinal pathogens- every twenty.

The hepatocytes (liver cells) last much longer: between six months and a year. Although it is part of the digestive system, the liver is in fact a different organ and although hepatocytes are the cells that produce bile (essential in the intestinal digestion of fats), its main functions are metabolic: they have innumerable headquarters in them metabolic processes whose scope of influence is the whole organism.

Blood cells have very different renewal rates. The shortest-lived are those of the immune system: neutrophils, which are the most abundant leukocytes, are renewed between every one and five days, and other leukocytes, the eosinophils, between every two and five. The platelets, whose function is to facilitate the healing of wounds, live about ten days. And much more long-lived are the red blood cells, which are renewed every four months. The hematopoietic stem cells, from which the previous ones come, remain under this condition for two months before becoming leukocytes, platelets and red blood cells.

Other relatively short-lived cells are those of the cervix, which last six days; from the pulmonary alveoli, eight days; of the epidermis of the skin, between ten and thirty days. More prolonged is the existence of osteoclasts, the cells that reshape the bone: they are renewed every two weeks; and even more that of the osteoblasts, those that produce it: they are replaced every three months. The activity of these cells results in 10% of the bone tissue being renewed every year. The cells of the trachea do it every one or two months. And the sperm every two months, although, by contrast, women are born with all their eggs.

Those that are less renewed are the adipocytes - cells that store fat reserves - that do it every eight years; the muscles, every fifteen; and the cardiomyocytes (muscle cells of the heart) undergo a renovation of between 0.5% and 10% per year. The neurons of the central nervous system are hardly renewed; the exception is the daily replacement of some seven hundred cells of a very specific area called "hippocampus", which implies that this area replenishes 0.6% of its neurons per year. On average, the body is renewed whole every 15 years.

If we think about it a bit, we live in a certain frenzy of permanent replacement of some - almost all, in fact - of our collective structures. It could even be said that we are not the same organism that we were a couple of months ago.