Biological Boundaries and Biological Age

Abstract

The chronologic age classically used in demography is often unable to give useful information about which exact stage in development or aging processes has reached an organism. Hence, we propose here to explain in some applications for what reason the chronologic age fails in explaining totally the observed state of an organism, which leads to propose a new notion, the biological age. This biological age is essentially determined by the number of divisions before the Hayflick's limit the tissue or mitochondrion in a critical organ (in the sense where its loss causes the death of the whole organism) has already used for its development and adult phases. We give a precise definition of the biological age of an organ based on the Hayflick's limit of its cells and we introduce a desynchronization index (the cell entropy) for some critical tissues or membranes, which are mainly skin, intestinal endothelium, alveoli epithelium and mitochondrial inner membrane. In these actively metabolising interface tissues or membranes, there is a rapid turnover of cells, of their cytoplasmic constituents such as proteins, and of membrane lipids. The boundaries corresponding to these tissues, cells or membranes have vital functions of interface with the environment (protection, homeothermy, nutrition and respiration) and have a rapid turnover (the total cell renewal time is in mice equal to 3 weeks for the skin, 1.5 day for the intestine, 4 months for the alveolae and 11 days for mitochondrial inner membrane) conditioning their biological age. The biological age of a tissue is made of two major components: (1) first, its embryonic age based on the distance (in number of divisions) between the birth date of its first differentiated cell and the time until it reaches its final boundary at the end of its development and (2) second, its adult age whose complement until its death is just the lapse of time made of the sum of remaining cell cycle durations authorized by its Hayflick's limit. From this definition, we calculate the global biological lifespan of an organism and revisit notions like demographic survival curves, duration and synchrony of cell cycles, living boundaries from proto-cells to organs, and embryonic and adult phases duration.

Macro- and micro-level predictors of age categorization: results from the European Social Survey

“…Researchers have attempted to define biological age, using physical or biological indicators, such as maximum breathing capacity, visual acuity, reaction time, or the division of cells (Demongeot 2009;Mitnitski et al 2002). These indicators correlate well with visible signs of aging, suggesting for example, that individuals who appear old also have deteriorated physical abilities and worse health status (Barrett 2003;Borkan and Norris 1980).…”

Modelling and Image Processing of Constriction and Proliferation in the Gastrulation Process of Drosophila melanogaster

“…In both these cases, a couple of morphogens acting often simultaneously i n opposit e (e. g. a coupl e of acti vat or and inhibitor like BMP-7 and BMP-2 in feather morphogenesis in the chicken [24][25][26][27] can induce the chemotactic motion of fibroblats or the biosynthesis of the elements constituting the auto-assemblage (like proteins and phospholipids). The fact that for a certain value of their viscosity ratio, the morphogens can coexist for a relatively long time in a precise location can greatly favor the birth of anatomic organ boundaries.…”

Demography and Diffusion in Epidemics: Malaria and Black Death Spread

“…The introduction of the space in Ross-McKendrick models can be made through stochastic spatial Markovian or renewal models (Demongeot and Fricot 1986), or deterministic Partial Differential Equations (PDE) in which the diffusion of hosts or vectors is modelled by the Laplacian operator D or possibly the d'Alembertian h, when some sub-populations can present an accelerated ageing (Demongeot 2009). These models are called SIGR with Diffusion (SIGRD) (de Magny et al 2005).…”

“…dt. When the biological age is defined by physiology of cells and tissues (Demongeot 2009) with the possibility to remain in the same age between t and t ? dt (despite of the fact that the chronological age is increasing of dt), then b ?…”

“…To be more precise in introducing the age classes, in particular with the biological age, we have before to recall the classical models used for modelling the population growth (Doliger 2006;Demongeot 2009). …”