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The
Human Digestive System |
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Organs
of the Alimentary Canal
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Organ
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Enzymes
Present
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What
Happens Here
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mouth
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amylase
(in saliva)
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mechanical
digestion of all food (teeth chewing
& grinding)
chemical digestion of carbohydrates
begins
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esophagus
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none
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food
passes from mouth through the esophagus
to the stomach
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stomach
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pepsin
gastric juice
hydrochloric acid (HCl )*
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mechanical
digestion of food (churning of stomach
walls)
chemical digestion of proteins begins
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small
intestine
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pancreatic
juice
intestinal juice
bile*
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chemical
digestion of carbohydrates, proteins,
& lipids continues & is completed
the small, soluble nutrients (sugars,
amino acids, fatty acids) are absorbed
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large
intestine
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none
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water
is absorbed from unusable, indigestible
wastes (feces)
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rectum
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none
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feces
are temporarily stored
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anus
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none
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feces
are eliminated (egested) from the
body
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The
human digestive system is made up of a long tube,
along which there are several organs that specialize
in breaking up they myriad components of food. Among
these organs are the salivary glands, esophagus, stomach,
pancreas, liver, small intestine, large intestine,
the rectum and anus. The primary reason for having
such a complex and varied system is that it allows
the human body to maximize its digestive efficiency.
Different components are handled along each segment
of the tract. As food passes through each digestive
site, specific nutrients are extracted and then transported
to either storage pathways or metabolic pathways.
The
digestive system carries out six basic processes;
ingestion, secretion, propulsion, digestion, absorption
and defecation.
Ingestion
is taking food into the mouth. Secretion is
the act of expelling a liquid. The cells lining the
alimentary canal secrete about 9 liters (9.5 quarts)
of water, acid, buffers, and enzymes each day to lubricate
the canal and aid in the process of digestion. Propulsion
consists of alternating contraction and relaxation
of smooth muscle in the walls of the alimentary canal
to squeeze food downwards.
Digestion
has two parts, mechanical and chemical. Mechanical
digestion is chewing up the food and your stomach
and smooth intestine churning the food, while chemical
digestion is the work the enzymes do when breaking
large carbohydrate, lipid, protein and nucleic acid
molecules down into their subcomponents -these and
others are the nutrients-. Absorption occurs
in the digestive system when the nutrients move from
the gastrointestinal tract to the blood or lymph.
Defecation is the process of expelling what
the body couldn't use..
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Inside
the villi are two types of vessels, capillaries
& lacteals. (The capillaries look like a
"web" around the lacteal.) The end products
of protein & carbohydrate digestion (namely
amino acids & simple sugars) are absorbed
into the capillaries. The end products of lipid
digestion (fatty acids & glycerol) are absorbed
into the lacteals, which are part of the lymph
system. The nutrients are then circulated to
body cells where they are used for growth, energy,
etc.
Why
do I have Gas?
Everyone
has gas. Burping or passing gas through the
rectum is normal. Because it is embarrassing
to burp or pass gas, many people believe they
pass gas too often or have too much gas. They
do not realize that passing gas 14 to 23 times
a day is normal. An occasional burp during or
after meals is normal, too. It is rare for a
person to have too much gas.
Most
of the time gas is odorless. The odor comes
from sulfur made by bacteria in the large intestine.
Sometimes gas causes bloating and pain. Not
everyone has these symptoms. It probably depends
on how much gas the body makes and how sensitive
a person is to gas in the large intestine.
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