The small intestine does all the absorbing,
right ? Much of the absorbing does occur in the small intestine, but not
all. The colon, or large intestine is where some very important absorption
Digestive enzymes, water, and minerals are reclaimed in the large intestine.
Microorganism that are healthy GI inhabitants complete the digestion of
many foods within the colon.
As a result, the human absorbs both free form amino acids and short chain
fatty acids from the colon.
Methylmercury has a carbon chain that is the same as found in a fatty
acid. This similarity is no doubt what makes methylmercury so fat soluble.
The reason all of this is important is that the colon is the most compelling
site for inorganic mercury to be formed into methylmercury by E. coli and
Candida yeast. Methylmercury formed in the colon will be rapidly absorbed
just like a short chain fatty acid.
"Appearance of 15N-labeled intestinal microbial amino acids
in the venous blood of the pig colon."; Am J Vet Res; 40:5; 1979
May; 716-8; Niiyama M; Deguchi E; Kagota K; Namioka S.
"Two experiments were done to determine whether pigs possess the ability
to absorb amino acids synthesized from urea nitrogen by indigenous microbes
in the large intestine. Incorporation of [15N] urea into amino acid fractions
of bacterial cells from the rectum and of deproteinized incubated medium
were examined in an experiment in vitro. The isotope was incorporated into
17 amino acids and the ammonia fraction of these samples. The absorption
of the microbial amino acids from the colon was investigated by the determination
of the 15N concentration of the free amino acids in the venous blood of
the colon after infusion of the 15N labeled microorganisms into the cecum.
The increase of 15N concentration was also observed in the plasma free amino
acids (threonine, isoleucine, phenylalanine, lysine, histidine, arginine,
aspartic acid, serine, alanine, cystine) of the blood from the colic branch
of the ileocolic vein. The results of these experiments indicated that pigs
have the ability to utilize the microbial amino acids synthesized from the
urea nitrogen in the large intestine."
"Functions of the Large Bowel"; Sidney F. Phillips; Gastroenterology
Unit, Mayo Clinic, Rochester, Minnesota 55905, USA
"The large intestine has been studied rather less than the other portions
of the alimentary canal for several reasons: a) considerable variations
occur among species in the anatomy of the large bowel ad in the absorptive
contributions of the hindgut to homeostasis; b) in most species, the transit
of colonic contents and the interactions between mucosa and contents are
more complex than those occurring in the small bowel; and c) the existence
of a rih microbial flora, which is of considerable importance ecologically,
complicates the experimental approaches to colonic function and the interpretation
of results. The colon possesses efficient mechanisms for sodium and chloride
absorption, and an exchange of bicarbonate for luminal chloride is important.
Absorptive function in the large bowel must also encompass the activities
of faecal enzymes. By modifying faecal substrates, of both endogenous and
exogenous origin, the flora facilitates and modifies absorption by the colon:
in some species these events are important nutritionally. On the other hand,
under pathophysiological conditions, the colon can secrete electrolytes
and water. Storage and transit in the colon are also complex, relative to
these phenomena in other areas of the gut. A major portion of the total
mouth to anus transit time occurs in the colon, where to and fro movement
of the contents is noticeable. Perhaps these complex movements facilitate
absorption by allowing optimum contact between contents and mucosa. The
colon also delivers material to the rectum in a manner whereby the distal
bowel can prepare stools for convenient evacuation. Despite these difficulties,
research is advancing our comprehension of the colon, its multiple and diverse
functions and the possibilities for alterations of function leading to disease."
1. Volatile fatty acids. Over 90% of these acids are comprised of acetate,
propionate, and butyrate; they are generated by the action of bacterial
enzymes on polysaccharides.
2. Volatile fatty acids (VFA) are well absorbed from the human large bowel.
3. Bacterial enzymes also deconjugate bile acids, hydrolizing the peptide
bonds between the bile acid nucleus and the amino acid conjugate moeity
(taurine or glycine). Deconjugation increases the lipophilic properties
of bile acids, facilitates their re-absorption by the gut, and could thus
modify enterohepatic of the bile acid pool.