This is an abridged write-up on the role of the appendix
written in part to answer Professor Dr. Andrew Charles Gomez, a very well-known ENT
surgeon, whose question to me was, whether I agree with him that the appendix
serves as a store house for beneficial bacteria, and has a role in nutrition.
I was asked for my opinion.
I fully concur with what Prof Gomez commented to questions
asked in a round of mail exchanges circulated among friends, scientific and medical colleagues in a
Whatsapp group.
EVOLUTIONARY BIOLOGY:
Here is my opinion as an extension on evolutionary biology I
recently studied, in that the appendix has evolved as part of a useful
component of the gastrointestinal gut shown in several mammalian lineages,
including probably in some of the earliest humanoids, the Neanderthals some 150
– 200 thousand years ago, and in the early homo sapiens according to anthropological
and fossil records.
According to some more recent studies, this evolutionary
linkage has persisted for thousands of years and has never disappears entirely.
This suggests that the appendix may have served an adaptive purpose in gut
physiology in all these mammalian species, including for modern humans for a very long evolutionary period in time.
Some previous studies on embryonic development, and into intrauterine
life till about 1 -2 years post neonatal life in humans, as well as in many
mammals, the appendix is statically-significantly larger by about 35 – 43 %
than in adults.
EARLY INFANT NUTRITION:
This suggests that the appendix may play a very important
role the early stages of early life support as part of the immunological
defenses, as well as its role in paediatric nutrition when beneficial gut microbiota
(gut bacteria) and pathogenic bacteria begin to establish themselves, often in
competition with each other for their colonic habitat.
One purpose I hypothesize is that, in infant nutrition for
the new born, milk sugar (lactose) in milk requires an enzyme (lactase) to
breakdown for it to be bio-available to babies.
In adult humans who stop drinking milk post-weaning period, this
enzyme may cease to produce, in that there would be no more epigenetic influence
of the lactose in milk on specific genes that express the lactase needed to
digest the milk sugars.
As a clinical sequel in
adult humans, especially among the Chinese and non-milk drinking Asians, they
develop milk intolerance due to lactase deficiency as one of the reasons. There are also other genetic factors being considered.
This role of lactase
is then taken over by the gut bacteria such as lactobacilli to break down the
milk sugar to make it available to infants (humans as well as babies of
mammals).
Notwithstanding, milk intolerance in adults may be offset by
the consumption of yogurt, fermented products and lactobacilli and the use of
probiotics immediately following an ingestion of large quantity of cow’s milk for
those who are lactose intolerant.
In infantile life, useful gut flora is supplied by the increased
appendix size to total colon surface area ratio. There it serves as larger pouch and
reservoir to shelter a larger populations of microbiota more effectively than what the rest of
the colon’s ability.
It is the constant abrasive actions of the peristaltic
contractions and motility of the intestines on colonic residues that constantly remove
large population of gut flora, compared to the safe harbor of an inactive “vestigial”
appendix.
It has been my personal opinion on evolutionary biology, that
it has been designed this way for the purpose of digestion of milk and the bio-availability other
highly complex sugars and starches that would not have been possible in a
highly motile colon.
GUT MICROBIOLOGY:
However, as the mammalian species (includes humans) grow,
the microbiota too multiple proportionally, and they migrate towards the much larger surface area
of the colon outside the appendix where space is not confined in a pouch, and where
nutrients are limited. There outside the appendix the colonies of bacteria
thrive best.
As a sequel, the appendix by natural design, atrophies into
a vestigial part of the colon, serving as if it has no more physiological function.
As the milk-breaking as well as the complex starch breaking
bacteria population shrinks and migrate from the now smaller appendix compared
to the larger surface area of the large intestines, pathogenic bacteria gets into
the appendix, and occupy the vacant
space where there is now lesser bacterial competition.
This is where and when opportunistic infections get hold,
and where lymphoid tissue and antibodies are in decline, causing the notorious
and common appendicitis.
It is unfortunate that bacteria multiply and spread into the
much larger areas of the colon where food is aplenty and vacating an enclosed
isolated appendix may not be the best evolutionary option for the individual.
One of the reasons for the migration is that, immune bodies
in higher amounts are found in the appendix, but in lesser amounts in the lymphoid
tissues of the colon and in the cecum.
Higher challenge by lymphoid tissues may not be adaptive for the beneficial gut flora. It is part of an adaptive response when environment becomes hostile.
Higher challenge by lymphoid tissues may not be adaptive for the beneficial gut flora. It is part of an adaptive response when environment becomes hostile.
This suggests that, that part of the vestigial colon has actually an
immunological function since high concentration of lymphoid tissues is also
found especially in the early stage of infantile development.
We know that the presence of lymphatic tissues and
antibodies in the colon, cecum and appendix may promote the growth of
beneficial microbiota and probiotic, such as Lactobacillus, Bifidobacterium which
is extremely useful for colon health as well as in the synthesis of certain
vitamins like folic acids.
In my opinion, combining what we already know in advances in gastrointestinal
physiology, infant nutrition, gut microbiology, immunology and in evolutionary
biology, I think the appendix has a well-deserved place in the biological evolution
for the well-being of colonic health,
and thus cannot be labeled as a vestigial part of the colon as most scientists and medical experts think.
After all we have our own independent thinking, and we need
to gather information from other areas of biomedical sciences as well and not just seen in one small corner of specialized medical or scientific discipline to
resolve this age-old theory that the appendix is a vestigial organ with no
physiological role. We need to think out of the box, and not be intellectually stagnant
The only problem is when it gets infected by impacted food
lodged there. That is when the classical appendicitis is presented, and needs
to be surgically addressed.
But then we will also lose part of our developmental immunological system in that part of the anatomy which may initiate the risk of colorectal cancer? This is another area of interest
But then we will also lose part of our developmental immunological system in that part of the anatomy which may initiate the risk of colorectal cancer? This is another area of interest
I hope I have been of some help to your questions Prof Dr.
Gomez. But I do concur with your
suggestion that the appendix has a role in gut nutrition.
Congratulations to you for your similar thinking!
Lim ju boo, Post-doctoral CE Cert. in Evol. Biol. (University of Cambridge)
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