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The cellularity of the bone marrow does decrease with age and can be usually calculated by the formula 100-age, and this seems consistent with a stem cell theory of aging. [18] A dog study published by Zaucha J.M, Yu C. and Mathioudakis G., et al. also shows evidence against the stem cell theory. Experimental comparison of the engraftment ...
The theory is based on the idea that ageing occurs over time due to the damage of the DNA. As an example, studies of mammalian brain and muscle have shown that DNA repair capability is relatively high during early development when cells are dividing mitotically, but declines substantially as cells enter the post-mitotic state. [28] [29] [30]
During differentiation, stem cells change their gene expression profiles. Recent studies have implicated a role for nucleosome positioning and histone modifications during this process. [38] There are two components of this process: turning off the expression of embryonic stem cell (ESC) genes, and the activation of cell fate genes.
A stem cell possesses two properties: . Self-renewal is the ability to go through numerous cycles of cell division while still maintaining its undifferentiated state. Stem cells can replicate several times and can result in the formation of two stem cells, one stem cell more differentiated than the other, or two differentiated cells.
The DNA damage theory of aging proposes that aging is a consequence of unrepaired accumulation of naturally occurring DNA damage. Damage in this context is a DNA alteration that has an abnormal structure. Although both mitochondrial and nuclear DNA damage can contribute to aging, nuclear DNA is the main subject of this analysis.
Senescence (/ s ɪ ˈ n ɛ s ə n s /) or biological aging is the gradual deterioration of functional characteristics in living organisms. Whole organism senescence involves an increase in death rates or a decrease in fecundity with increasing age, at least in the later part of an organism's life cycle.
Reproductive exhaustion theory of aging; Reproductive-cell cycle theory; S. ... Stem cell theory of aging; Stereotype embodiment theory; T. Telomere theory of aging; V.
(a) The survival rate within a population decreases with age, while the reproduction rate remains constant.(b) The reproduction probability peaks early in life, at sexual maturity, and then steadily decreases as an individual ages, with the remaining share of the population decreasing with age as they enter the selection shadow.
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