Tissue regeneration falters with age throughout the body, and there are numerous contributing factors to this decline. It is uncertain as to exactly how these factors layer in terms of cause and effect, however. One can point to the loss of stem cell activity, for example, and then ponder the degree to which that is secondary to rising levels of chronic inflammation. That chronic inflammation is in part inherent disarray and misconfiguration in the immune system stemming from exposure to persistent pathogens, but also arises from the accumulation of senescent cells that secrete strongly inflammatory signals. Now consider that immune cells are generated by stem cells and that one of the jobs of the immune system is to remove senescent cells, and you can see why it becomes challenging to definitively assign causes and consequences when examining the messy later stages of aging. Everything influences everything else, and many dysfunctions interact with one another to form feedback loops.
When it comes to regeneration in mammals, the liver is something of a special case. It is highly regenerative, the only organ that in adults
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