>Are there other triggering mechanisms for apoptosis? Is the phenomenon true
>in all cells? Smooth muscle cells? Brain cells? Or is it limited to
>epithelial/epidermal tissues or single-celled organisms?
If I've got it right then apoptosis is unique to multi-cellular organisms.
Suicide in single-celled organisms have no biological function. All
multi-cellular cells are programmed to commit suicide right after cell division,
but this process may be delayed/stopped by certain control chemicals in the
environment. Some cells therefore never commit suicide and are never replaced
(e.g. neurons).
>Assuming apoptosis in multi-cellular entities is a universal biologic
>phenomenon, I'm not sure how such "planned obsolescence" of organism
>components adds to the organizational properties of an organism--- the
>process of repair and replacement of injured/damaged components is already
>part of the system. What is added by the "cancellation principle" you
>mentioned?
Apoptosis has two functions in two different phases of the organisms lifecycle.
The most obvious is the phase of self-maintenance, of developmental stasis.
Mitosis/Apoptosis here plays the role of continuous renewal of the multicellular
organism and large scale repair (healing wounds etc.) The other and most
important role of Mitosis/Apoptosis is the self-organized self-regulated
developmental process of multicellular organisms. By controlling the rate of
Mitosis/Apoptosis in different regions of the growing fetish, new forms may
emerge. For instance, the cell death rate is greater in some regions of the
embryotic hand than in others. These regions eventually becomes the space
between our fingers. A such, the Mitosis/Apoptosis cancellation is directly
involved in the development of multicellular form. As I said, it is crucial.
Without it we'd all be a bunch of undifferentiated lumps of meat.
This principle is so deep and general that there is reason to believe it is
fundamental to all of life. Death follows in the wake of birth, leaves fall of
in the fall and new ones grow out in the spring, species go extinct and new ones
pop into existence. All this suggests that the conditions for larger scale
organizational closure are satisfied. In this sense life on earth is not
"untamed", there is a natural self-taming in the cancellation of all kinds of
growth. Therefore, while death may be an evolutionary accumulated imprecision it
is also a very common biological "plan" and has important biological functions
on all scales of life.
Onar.