Biological complexity: total cells in a human (Introduction)

by David Turell , Thursday, September 21, 2023, 17:28 (219 days ago) @ David Turell

How fast do they reproduce:

"'Most of the skin and gut are replaced very fast, most likely within months," Olaf Bergmann, a principal researcher in the Department of Cell and Molecular Biology at the Karolinska Institute in Stockholm, Sweden, told Live Science in an email. Cells in the liver regenerate at a somewhat slower pace, Bergmann and his colleagues reported June 15 in the journal Cell Systems. For the study, the authors analyzed liver tissue using radiocarbon dating and found that most liver cells are replaced within three years.

"However, cells in other organs and systems are even slower to replicate and lag behind the seven-year cut-off.

"For example, "the human heart renews at a rather low rate, with only 40% of all cardiomyocytes [the cells responsible for the contracting force in the heart] exchanged throughout life," Bergmann said. Skeletal cells, meanwhile, need around 10 years to replicate a skeleton in its entirety, according to the New York Times.

"In the brain, cell renewal can be even more leisurely. Scientists have uncovered evidence showing that some neurons in the hippocampus are renewed, but only at a rate of 1.75% annually, according to a 2013 study in Cell. And some types of neurons within the striatum also regenerate, according to a 2014 study in Cell. But other types of neurons stay with a person for their entire lifetime, Bergmann said. And even the distinct cell populations that can rejuvenate are not replaced entirely, but only partly over a lifetime, he said."

How many cells:

https://www.livescience.com/health/anatomy/how-many-cells-are-in-the-human-body-new-stu...

"According to a new analysis of more than 1,500 papers, the average adult male human has around 36 trillion cells — that's 36 followed by 12 zeros — while adult females have 28 trillion and 10-year-old children have about 17 trillion. To arrive at these estimates, the authors of the new study, which was published Monday (Sept. 18) in the journal PNAS, considered the size and number of 400 types of cells in the body across 60 tissues, including muscle, nerve and immune cells.

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"'Possibly most critical is our estimate of the total number of human lymphocytes, which are vital for our immune function," he said. "We estimate 2 trillion lymphocytes in the human body which is four times higher than prior estimates and could prove important in lymphocyte-related health and disease, such as HIV or leukemia.'"

Comment: Several trillion cells reproduce every day or so. New mutations, mainly as mistakes occur infrequently. Much rarer mistakes result in cancer. The editing systems keep these mistakes at a very low ratio compared to the rate of cell splitting on a daily basis. This is the answer theodicy articles give to complaints about God's works: it is the only system that works. To enjoy this life we must accept it .