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Greetings majestic and august CSers,
SMALL INTESTINE, action of organisms
Under normal conditions and on a mixed diet, carbohydrate fermentation
is the characteristic action of the organisms in the small intestine,
while protein putrefaction occurs in the large intestine. The reason for
this seems to be that carbohydrates serve to protect proteins because
some of the organisms of the small intestine, i.e.,bacillus coli, will
not attact proteins as long as carbohydrate material is present. In
addition , the organic acids produced by the fermentation of
carbohydrates tend to neutralize the alkalinity of the intestinal
secretion and may even give an acid reaction. An acid reaction is
unfavorable to the action of the organisms that hydrolyze proteins, and
in this way putrefaction in the small intestine is prevented. It seems
that the nature of organismal activity in the small intestine depends
partly upon the character of the diet,which,therefore, may be chosen so
as to favor one or the other kind.
The *bacillus acidophilus* is the species best adapted to maintaining
good intestinal conditions. The ingestion of cultures of this organism
and the liberal consumption of lactose, which is favorable to their
development, often assist in establishing good intestinal hygiene.
Bacteria are present in large numbers on the walls of the stomach and
intestine, and many are also found in the intestinal contents. Vitually
all the bacteria of the intestine are either *obligate* or
*falcultative* anaerobes. The obligate anaerobic bacteria include many
long thin ,Gram-negative rods which are as yet unnamed, as well as
species of *Clostridium* and *Bacteroids*. Faculative anaerobes include
*Escherichia coli* and *Streptococcus faecalis*.
In the lower small intestine and colon, water is gradually removed
from the digesting mass, and the material converted into feces, the
excretory product. Bateria, chiefly dead ones, make up about one-third
the weight of feces.
The bacteria that grow in the large intestine are responsible for the
gases and odors produced in and expelled from the large intestine. The
gases are primarily nitrogen, cardon dioxide, methane, and hydrogen, the
odors are primarily due to hydrogen sulfide, indole, and skatole. A
normal human expells about 450 to 650 ml of gas per day, composed of
about 40% carbon dioxide, 50% N2 and small amounts of methane and
hydrogen. The N2 comes from the air and the CO2, methane, and hydrogen
come from bacterial fermentation.
When some antibiotics are given orally, they may enter the intestine
and prevent the growth of intestinal bacteria. As the intestinal
contents move downward, the inhibited intestinal bacteria are expelled,
leading to the near-sterilization of the intestinal tract. Antibiotics
given orally are thus often used to sterilize the intestinal tract
before bowl or intestinal surgery. In the absence of this normal flora,
exotic bacteria such as antibiotic-resistant *Staphylococcus aureus* or
the yeast *Candida albicans* may become established. Normally, these
organisms do not grow in the intestine because they cannot compete with
the normal flora, but with the normal flora eliminated, they can take
over. Occasionally, establishment of these exotic organisms can lead to
harmful alteration in digestive function, but in the absence of
continued antibiotic therapy, the normal flora will eventually become
reestablished.
The composition of the intestinal flora is influenced by diet. Thus
breast-fed infants have a flora consisting largely of the organism
*Bifidobacterium bifidus*, which requires a growth factor found in
mothers milk but not cows milk. Infants fed cows milk usually have a
more complex flora. A major constituent of milk is the sugar lactose,
and many of the bacteria in the large intestine can utilize lactose for
growth. In adults, whose milk consumption is lower, lactose-utilizing
bacteria represent only a small part of the normal flora.
The stomach is normally free of microbial growth because of its acid
content. Microorganisms are much more plentiful in the large than in the
small intestine.
A baby is born with a sterile intestinal tract, with the first
feeding, bacteria are introduced. If the child is breast fed, the
predominating organism is Lactobacillus bifidus. Bacteria of the genus
Lactobacillus convert carbohydrates to lactic acid. If the child is
bottle fed, Lactobacillus acidophilus predominates. In addition other
bacteria are present.
Here is a listing of the major *resident microbes* of the
gastrointestinal tract,remember the stomach is mostly free of microbes.
Coliforms, enterococci, clostridium species, proteus species, yeasts,
penicillium species, enteroviruses, pseudomonas aeruginosa, aerobic and
anaerobic streptococci, staphylococci, enterococci, alcaligenes
faecalis, bacteroides species, lactobacillus species.
VILLI
As the mixture of food , bile, and pancreatic enzymes passes through
the small intestine, maltose, peptides, fatty acids,glycerol,and fat
droplets are produced. The final digestion and absorption of these
materials is the function of the *villi*, which line the inner surface
of the small intestine. The villi increase the surface area many times
what it would be if it was a simple smooth tube. In addition, the
exposed surface of the epithelial cells of each villus is covered with
projections, The *microvilli* or "brush border". Thanks largely to these
the total surface area in the intestine is about 100 sq. ft., five times
the surface area of the exterior of the body. Incorporated on the
surface of the microvilli are a number of enzymes that complete the
digestion process. A number of *aminopeptidases* complete the hydrolysis
of peptides into amino acids. These enzymes act in a manner similar to
carboxypeptidase but attack the amino (NH2) end of the peptide molecules
instead of the acid end.
Three dissacharidases localized on or in the microvilli hydrolyze the
dissacharides maltose,sucrose, and lactose into their component
monosaccharides. Each maltose molecule is split into two glucose
molecules and thus glucose is the end-product of the digestion of
starch. Sucrose (table sugar) gives a molecule of glucose and one of its
isomers, fructose, while lactose (milk sugar) gives glucose and
galactose. With the actions of these enzymes, protein and carbohydrate
digestion comes to an end. What were originally macromolecules have now
been coverted into small molecules, amino acids and monosaccharides,
ready for passage into the bloodstream via the interstitial fluid and
lymph.
Bless you Bob Lee
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oozing on the muggy shore of the gulf coast
[email protected]
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