Ask A Scientist Molecular Biology Archive

name         Pamela
status       other
age          50s
       
Question -   I notice in a previous answer your Biologist claims the 
appendix is a useless vestigial organ. I ask you to access 
Medline, for a 
report from last year, about the need for the appendix to 
drain toxins 
from the bowel by osomosis into the mesenteric lymph duct in 
the region 
of the ileocecal valve (which at times does not work properly). 
 
Has any of this information about "draining toxins" been verified?
------------------------------------------------
Dear Pamela:

Rather than being an industrial-scale "drain" for toxins, it would be
more correct to think of the specialized structures of the appendix as a
micro-scale sampling port for the immune system.  

Although we depend on the intestine to absorb nutrients from our food,
its surface is remarkably well sealed up to keep out harmful substances
and organisms.  The exception to this are the regions containing
lymphoid follicles, which are dense accumulations of lymphocytes.
Overlying these structures are specialized epithelial cells called "M
cells."  These cells actively take up particles and dissolved molecules
from the inside of the intestine and transport them across the
epithelial layer to its underside, where lymphocytes and other cells
wait nearby.  This provides a pathway through which the cells of the
immune system can "see" what substances are present in the intestine.
From here, tissue fluids are collected into thin-walled lymphatic
vessels that take it to the mesenteric lymph nodes, and through some
other lymphoid plumbing, eventually to the bloodstream.  This allows
some of the foreign material, and the lymphocytes that have reacted to
it, to reach distant parts of the body.  This movement is far from
random, though.  We often speak of the "mucosal immune system" because
lymphocytes that were stimulated near one kind of mucosal surface tend
to return there, or to another mucosal surface.  Especially in the case
of infectious organisms that typically enter the body through food,
drink, or air, researchers are working hard to develop vaccines that
take advantage of the "mucosal immune system."  These would typically be
given nasally or orally, instead of as a shot.  

You might think, "If this 'window' exists in the lining of the
intestine, why can't bacteria and viruses enter the body through it?"
The good news is that if they do, they come out at the base of the M
cell only to find themselves looking directly into the teeth of the
assembled powers of the immune system!  The bad news is that some
organisms, including poliovirus and pathogenic E. coli, do seem to be
able to take advantage of this chink in our armor. 
Tom Douglas 
=========================================================
Usually the appendix is described as having no KNOWN function.  This is a
way
scientists can cover themselves in the event that a function is discovered
sometime in the future.  It is entirely possible that a function will or has
been found.  I too had been taught that the appendix was possibly vestigial,
but I would be interested if your information can be verified.

vanhoeck
=========================================================
As a histologist I see no reason to consider the v. appendix as having no
function since it contains numerous lymphoid follicles that produce
functional lymphocytes and a rich blood supply to communicate them.  The
general idea of vestigial organs is to me a measure of ignorance, arrogance
and lack of imagination. Ignorance in that we label it as such because we do
not know its function; arrogance in that we declare it of no value since we
can see none; and lacking in imagination in so far as when we cannot see its
function cannot imagine one.  I call your attention to that other "vestigial
organ" the thymus without which, in early life, we would produce a severely
compromised cell-mediated immune system as the "nude" mouse and numerous
thymectomized mammalian studies have shown. Although some general reference
books still list the v. appendix as "vestigial" most immunologists (I
included) would strongly disagree!


Peter Faletra Ph.D.
Senior Science Advisor
Office of Science
Department of Energy
=========================================================