The Digestive System
By: Aubrey
Bibliography
http://celiacdisease.about.com
http://www.biology-online.org
http://www.nlm.nih.gov
http://www.britannica.com
http://en.wikipedia.org
http://www.buzzle.com
http://mechanicaldigestion.org
http://www.livestrong.com
http://www.enchantedlearning.com
http://www.webmd.com/
Mucus

Mucus is something everyone has, and
some people wish they had a lot less of
the stringy, gooey stuff. Sure, it can be
gross to blow globs of snot into tissue
after tissue when you have a cold or sinus
infection, but mucus actually serves a very
important purpose.
Chemical Digestion

Chemical digestion doesn't begin in your stomach, but in
your mouth. The moment you see, smell or even think
about food, your mouth begins to produce extra saliva.
Saliva contains an amylase enzyme called ptyalin, which
breaks starches down into dextrose and maltose by
adding a water molecule into the starch compound.
Once food is swallowed, powerful muscles in the
esophagus push it downward into the stomach in a
continuous wave motion.
Mouth

The digestive process begins in the
mouth. Food is partly broken down by the
process of chewing and by the chemical
action of salivary enzymes (these enzymes
are produced by the salivary glands and
break down starches into smaller
molecules).
Enzymes


Enzymes have extremely interesting properties that make them
little chemical-reaction machines. The purpose of an enzyme in a
cell is to allow the cell to carry out chemical reactions very quickly.
These reactions allow the cell to build things or take things apart as
needed. This is how a cell grows and reproduces. At the most basic
level, a cell is really a little bag full of chemical reactions that are
made possible by enzymes!
Enzymes are made from amino acids, and they are proteins. When
an enzyme is formed, it is made by stringing together between 100
and 1,000 amino acids in a very specific and unique order. The chain
of amino acids then folds into a unique shape. That shape allows
the enzyme to carry out specific chemical reactions -- an enzyme
acts as a very efficient catalyst for a specific chemical reaction. The
enzyme speeds that reaction up tremendously.
Mechanical Digestion

Mechanical digestion happens in the mouth with
the help of the saliva, teeth and tongue. It is the
actual break down of food into smaller bits. This
makes food easier to digest. The chemical
content of the food is extracted during the
process. This is largely carried out by by
digestive enzymes which are enzymes that break
down polymeric macromolecules into their
smaller parts, so that they can be absorbed by
the body.
Salivary Amylase

Amylase is an enzyme found in human saliva which is responsible
for the breaking down of starch into sugar. The process of digestion
begins with the chewing of food, in the presence of salivary amylase
in the mouth, to convert the starch in food to sugar. Foods that are
high in starch, like potatoes or bread, will taste slightly sweet when
chewed - this is because of the action of amylase. The enzyme
amylase is also secreted by the pancreas, where it is called
pancreatic amylase; its presence in the gastrointestinal tract aids in
the breakdown of food molecules into energy for the body to store
and use. The diagram of the digestive system will clarify the
sequence of digestion and also help in the identification of the
organs of the digestive system.
The Esophagus

The esophagus is a muscular tube connecting
the throat (pharynx) with the stomach. The
esophagus is about 8 inches long, and is lined
by moist pink tissue called mucosa. The
esophagus runs behind the windpipe (trachea)
and heart, and in front of the spine. Just before
entering the stomach, the esophagus passes
through the diaphragm.
The Stomach


The stomach is a muscular organ located on the left side
of the upper abdomen. The stomach receives food from
the esophagus. As food reaches the end of the
esophagus, it enters the stomach through a muscular
valve called the lower esophageal sphincter.
The stomach secretes acid and enzymes that digest
food. Ridges of muscle tissue called rugae line the
stomach. The stomach muscles contract periodically,
churning food to enhance digestion. The pyloric
sphincter is a muscular valve that opens to allow food to
pass from the stomach to the small intestine.
Gastric Juices

The gastric juice is made up of hydrochloric acid,
pepsinogen and other digestive enzymes,
intrinsic factor, gastrin, mucus, and
bicarbonates. It has a pH ranging from 1 to 2.
Its low pH is essential in activating many
digestive enzymes and in destroying various
pathogens. The gastric juice also contains
bicarbonates to neutralize the acid and thereby
regulate the pH level in the stomach.
Chyme

chyme, a thick semifluid mass of partially digested food and
digestive secretions that is formed in the stomach and
intestine during digestion. In the stomach, digestive juices
are formed by the gastric glands; these secretions include
the enzyme pepsin, which breaks down proteins, and
hydrochloric acid. Once food is in the small intestine, it
stimulates the pancreas to release fluid containing a high
concentration of bicarbonate. This fluid neutralizes the
highly acidic gastric juice, which would otherwise damage
the membrane lining of the intestine, resulting in a
duodenal ulcer. Other secretions from the pancreas,
gallbladder, liver, and glands in the intestinal wall add to
the total volume of chyme.
Villi

Microscopic finger-like projections that line
the inner wall of the small intestine.
(Singular: villus.) After food passes from
the stomach into the small intestine,
nutrients in the food are absorbed into the
body through the villi. Every person has
millions of villi in his intestines.
Small Intestine

The small intestine consists of three
sections. The first portion, called the
duodenum, connects to the stomach. The
middle portion is the jejunum. The final
section, called the ileum, attaches to the
first portion of the large intestine
Appendix


The appendix sits at the junction of the small intestine
and large intestine. It’s a thin tube about four inches
long. Normally, the appendix sits in the lower right
abdomen.
The function of the appendix is unknown. One theory is
that the appendix acts as a storehouse for good
bacteria, “rebooting” the digestive system after diarrheal
illnesses. Other experts believe the appendix is just a
useless remnant from our evolutionary past. Surgical
removal of the appendix causes no observable health
problems.
Duodenum



The duodenum is the first part of the small
intestine. It is located between the stomach and
the middle part of the small intestine, or
jejunum.
After foods mix with stomach acid, they move
into the duodenum, where they mix with bile
from the gallbladder and digestive juices from
the pancreas.
Absorption of vitamins, minerals, and other
nutrients begins in the duodenum.
Pancreas

The pancreas is about 6 inches long and sits
across the back of the abdomen, behind the
stomach. The head of the pancreas is on the
right side of the abdomen and is connected to
the duodenum (the first section of the small
intestine) through a small tube called the
pancreatic duct. The narrow end of the
pancreas, called the tail, extends to the left side
of the body
Liver



The liver is a large, meaty organ that sits on the right side of the
belly. Weighing about 3 pounds, the liver is reddish-brown in color
and feels rubbery to the touch. Normally you can't feel the liver,
because it's protected by the rib cage.
The liver has two large sections, called the right and the left lobes.
The gallbladder sits under the liver, along with parts of the pancreas
and intestines. The liver and these organs work together to digest,
absorb, and process food.
The liver's main job is to filter the blood coming from the digestive
tract, before passing it to the rest of the body. The liver also
detoxifies chemicals and metabolizes drugs. As it does so, the liver
secretes bile that ends up back in the intestines. The liver also
makes proteins important for blood clotting and other functions.
Bile/Bile Duct



A bile duct is any of a number of long tube-like
structures that carry bile.
Bile, required for the digestion of food, is
secreted by the liver into passages that carry
bile toward the hepatic duct, which joins with
the cystic duct (carrying bile to and from the
gallbladder) to form the common bile duct,
which opens into the intestine.
The biliary tree is the whole network of various
sized ducts branching through the liver.
Gall Bladder


The gallbladder is a small pouch that sits just under the
liver. The gallbladder stores bile produced by the liver.
After meals, the gallbladder is empty and flat, like a
deflated balloon. Before a meal, the gallbladder may be
full of bile and about the size of a small pear.
In response to signals, the gallbladder squeezes stored
bile into the small intestine through a series of tubes
called ducts. Bile helps digest fats, but the gallbladder
itself is not essential. Removing the gallbladder in an
otherwise healthy individual typically causes no
observable problems with health or digestion yet there
may be a small risk of diarrhea and fat malabsorption
Absorption

Absorption is the movement of molecules
across the gastrointestinal (GI) tract into the
circulatory system. Most of the end-products of
digestion, along with vitamins, minerals, and
water, are absorbed in the small intestinal lumen
by four mechanisms for absorption: (1) active
transport, (2) passive diffusion, (3) endocytosis,
and (4) facilitative diffusion. Active transport
requires energy.
Large Intestine

The large intestine (colon) extends from
the cecum to the anus and includes the
ascending colon, the transverse colon, the
descending colon, the sigmoid colon, and
the rectum.