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Many people spend a third of their time consciously trying to control
how to get food into their digestive tracts and another third thinking about
how that food is doing when it gets into their digestive tracts and another
third of their time consciously trying to control how to get their food
intake out of their digestive tracts. However, once food is swallowed, the
conscious ability to control the passage of food is almost completely lost.
When the food reaches the point of elimination some conscious control is
again reestablished in the digestive system.
The gastrointestinal track or as people call it, the digestive system, has
the main purpose of break down food, both solid and fluid into sustenance
for the various tissues and systems in the body. A normal digestive tract
squeezes the utmost benefit from what it eats. Feces are the products left
over when the body has selected everything that is of use from the food
that has been eaten.
The digestive system distance ranges from the mouth to the bottom of the
trunk, which when we look at it, seems like no more than two or three feet,
but is really about 30 feet and like a railway station consisting of signals,
checkpoints, and control devices in a turning, zigzagging, coiling track
system.
From the moment the three main types of food-carbohydrates, fats and proteins-enter
the mouth, they are exposed to chemical and mechanical actions that begin
to break them apart so that they can be absorbed through the intestinal
walls into the circulatory system.
What's Below
Chemical Digestion
Stomach
About 10 inches down the esophagus,
the swallowed food or bolus is now fairly well minced and turned into a
pulpy mass as it passes into the stomach. The function of the stomach is
best described as a food processing unit (similar to one you may have in
your kitchen) and a storage cistern. It looks like a deflated balloon when
empty, but when full, it becomes about a foot long and six inches wide able
to hold about two quarts of food and drink. Persons have been known, however,
to live a full life with part or even all of it removed. The stomach is
both chemical and mechanical. Various chemicals in the stomach like the
digestive enzymes pepsin, rennin, and lipase interact to break down the
food. In addition, hydrochloric acid creates suitable environment for the
enzymes and assists in the digestion. Also, watery mucus provide a protective
lining for the muscular walls of the stomach so it will not be digested
by the acid or enzymes. The mechanical action of the muscles in the stomach
constrict and relax in a continuous motion blending, whipping, and stirring
the stomach's contents into chyme, a pulpy substance that can be handled
by the small intestine.
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Small intestine
The small intestine is the longest organ of the digestive tract.
It is divided up indiscriminately into three sections: the duodenum,
the jejunum, and the ilium.
Duodenum 
This is the place where the ultimate destruction of food digestion
reaches its completion and where the acidity of chyme is nullified. The
nutrients in the food eaten many hours ago have almost been diminished to
molecules small enough to be absorbed through the intestinal walls into
the bloodstream. Carbohydrates are diminished into simpler sugars; proteins
to amino acids; and fats to fatty acids and glycerol. Enzymes are secreted
by the walls of the duodenum and unite with the bile (essential for the
digestion and absorption of tenacious fatty materials) and pancreatic enzymes
in the duodenum.
Jejunum
Peristalsis pushes the nutrient liquid out of the duodenum into
the first reaches of the jejunum. A greater number of villi , microscopic,
hair like structures, begin to absorb amino acids , sugars, fatty acids
and glycerol from the digested contents of the small intestine, and starts
them on their way to other parts of the body. This part of the small intestine
executes a digestive operation so that what is passed on to the large intestine
is a thin watery substance almost completely devoid of nutrients.
Ilium
This is the place which is about a third of the small intestine.
The greatest number of the estimated five or six million villi in the small
intestine are found along the ilium making it the main absorption locale
of the gastrointestinal tract. The villi here are always in a fretful movement:
oscillating, pulsating, lengthening, shortening, growing narrower then wider,
extorting every particle of nutrient.
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The Liver, Gallbladder, and Pancreas
Legitimately, these three organs lie outside of the gastrointestinal
tract. Nevertheless, digestive fluids from all three meet like intersections
of a railway track at the common bile duct, and their movement from there
into the duodenum is controlled by a sphincter muscle. The pancreas
is a producer of digestive enzymes. The gallbladder is a small reservoir
for bile. The liver reproduces nutrients so that they can be used
for cell-rebuilding and energy.
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Large Intestine
There is a merger between the illium
and the cecum, the first section of the large intestine. Any solid substances
that flow into the large intestine through the ileocecal valve (which prevents
back flow into the small intestine) are as a rule indigestible, or are bile
constituents. What the cecum primarily inherits is water.
What the large intestine essentially does, other than act as a passageway
for removal of body wastes, is to act as a provisional reservoir for water.
There are no villi in the large intestine and peristalsis is much less forceful
than in the small intestine. As water is absorbed, the contents of the large
intestine change from a watery liquid and are compressed into semisolid
feces. Nerve endings in the large intestine signal the brain that it is
time for a bowel movement. The fecal material moves through the colon
down to several remaining inches known as the rectum and out through
the anus an opening controlled by the outlet valves of the large
intestine. 
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Enzymes
| Site
of Enzyme Origin | Enzyme | Nutrient It
Breacks Down | Product Of Enzyme Action | Place
of Enzyme Action |
| Salivary Glands |
Salivary Almalase | Carbohydrates-sugars | Simple
Sugars | Mouth |
| Gastric glands
| Pepsin | Proteins | Amino Acids |
Stomach |
| Liver | Bile |
Fats/Lipids | Emulsifide Fats | Small Intestine |
| Samll Intestine | Maltase, Lactase, Sucrase
| Carbohydrates | Simple sugars | Small Intestine
|
| Pancrease | Trypsin, Lipase,
Amylase | Proteins, Fats/Lipids, Carbohydrates | Amino
acids, Glycerol/Fatty Acids, Simple Sugars | Small Intestine |
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Mechanical Digestion
Mechanical Digestion takes place in the mouth, where the the
saliva, teeth, and tongue all play an important role in this digestive process.
Saliva
The smallest taste, smell, and anticipation of food sends signals
to the brain. The brain in turn sends messages to a system of salivary glands.
Saliva is essentially made up of water and begins to soften up the food
so it can pass more smoothly down the throat. Besides water there is also
a very special substance, an enzyme called pytalin , whose main task
is to breakdown the food into simpler forms.
Teeth
The aftermath of the action of the teeth in digestion results
in two outcomes: havoc and devastation. The teeth are gears to demolish
chunks of food by a series of actions such as clamping, slashing, piercing,
grinding and crushing.The teeth do the first drastic destruction to food
in the digestive system.
Tongue
The tongue consists of four types of taste buds--salty, sweet,
sour, and bitter--and is a very maneuverable and pliable arrangement of
muscle. It helps to remove, and dislocate food particles in the teeth and
shifts food around in the mouth in order to assist with the all important
act of swallowing. The act of swallowing food, which at this place in the
system is called a bolus, brings many organs into action. As the top of
your tongue presses up against the hard palate , the roof of your
mouth, food is shoved to the back of the mouth. This action in turn brings
the soft palate and ursula (the place at the very back of the mouth
where there is a teardrop shape located) into action. They keep the food
from being misguided toward the nose. Once past the soft palate, the food
is in the pharynx, a train station with two tracks, one leading to
the trachea (windpipe), the other to the esophagus (food tube).
The epiglottis projects out from the trachea side and helps to admit
free movement of air as it is swallowed and at the same time restricts entrance
to the esophagus. The larynx, provides the epiglottis with most of
its muscle for movement. It applies an upward force that helps to relax
some tension on the esophagus, so that food enters where it is meant to
go, down the esophagus and not down the windpipe. Many people have experienced
at some time or another when the swallowing action did not go as it was
supposed to.
Cough. Cough. Choke.
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Peristalsis
This mechanical action has to do with sets of muscles that cooperate
to move both liquid and solid food along the digestive tract. In other word,
it pushes food along your esophagus, stomach, and intestine.. 
Gravitational pull is lessened in a sense when food
enters the esophagus because of peristalsis. Peristalsis helps a
person to swallow lying down or even standing on their head. Peristalsis
has another essential task besides assisting in the movement of food through
the body. It also helps to knead, agitate, and pound the solid residue that
is left after the teeth or those without teeth, the gums, have done their
best.
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Digestive Sphincters
The gastrointestinal tract is supplied with a number of muscular
valves. These control and direct the quantity of food that goes through
the digestive tract and inhibits the back movement of partially digested
food.
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©Copyright 1996