Good morning! Welcome to Duodenum Ad Agency. I am
Sunny Wang, your tourist guide during this 5 days tour
of human digestive system. Enjoy your time!
The human digestive system is a
complex series of organs and glands that
processes food. In order to use the food
we eat, our body has to break the food
down into smaller molecules that it can
process; it also has to excrete waste.
Most of the digestive organs (like the
stomach and intestines) are tube-like and
contain the food as it makes its way
through the body. The digestive system is
essentially a long, twisting tube that runs
from the mouth to the anus, plus a few
other organs (like the liver and pancreas)
that produce or store digestive chemicals.
The Digestive Process:
The start of the process - the 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).
On the way to the stomach: the esophagus - After being chewed and swallowed, the food
enters the esophagus. The esophagus is a long tube that runs from the mouth to the stomach.
It uses rhythmic, wave-like muscle movements (called peristalsis) to force food from the
throat into the stomach. This muscle movement gives us the ability to eat or drink even
when we're upside-down.
In the stomach - The stomach is a large, sack-like organ that churns the food and bathes it
in a very strong acid (gastric acid). Food in the stomach that is partly digested and mixed
with stomach acids is called chyme.
In the small intestine - After being in the stomach, food enters the duodenum, the first
part of the small intestine. It then enters the jejunum and then the ileum (the final part of
the small intestine). In the small intestine, bile (produced in the liver and stored in the gall
bladder), pancreatic enzymes, and other digestive enzymes produced by the inner wall of
the small intestine help in the breakdown of food.
In the large intestine - After passing through the small intestine, food passes into the large
intestine. In the large intestine, some of the water and electrolytes (chemicals like sodium)
are removed from the food. Many microbes (bacteria like Bacteroides, Lactobacillus
acidophilus, Escherichia coli, and Klebsiella) in the large intestine help in the digestion
process. The first part of the large intestine is called the cecum (the appendix is connected
to the cecum). Food then travels upward in the ascending colon. The food travels across
the abdomen in the transverse colon, goes back down the other side of the body in the
descending colon, and then through the sigmoid colon.
The end of the process - Solid waste is then stored in the rectum until it is excreted via the
anus.
The alimentary canal,
strictly speaking, is the
whole digestive tract from
the mouth to the anus.
In the human body, the mouth (oral cavity) is a specialized organ for receiving
food and breaking up large organic masses. In the mouth, food is changed
mechanically by biting and chewing. Humans have four kinds of teeth: incisors are
chisel-shaped teeth in the front of the mouth for biting; canines are pointed teeth for
tearing; and premolars and molars are flattened, ridged teeth for grinding, pounding,
and crushing food.
In the mouth, food is moistened by saliva, a sticky fluid that binds food particles
together into a soft mass. Three pairs of salivary glands—the parotid glands, the sub
maxillary glands, and the sublingual glands—secrete saliva into the mouth. The
saliva contains an enzyme called amylase, which digests starch molecules into
smaller molecules of the disaccharide maltose.
During chewing, the tongue moves food about and manipulates it into a mass
called a bolus. The bolus is pushed back into the pharynx (throat) and is forced
through the opening to the esophagus.
Tongue moves food about and
manipulates it into a mass called
a bolus. The bolus is pushed
back into the pharynx (throat)
and is forced through the
opening to the esophagus.
Teeth start the process of
physical digestion and pushes
chewed food to the pharynx.
Humans have four kinds of
teeth: incisors are chisel-shaped
teeth in the front of the mouth
for biting; canines are pointed
teeth for tearing; and premolars
and molars are flattened, ridged
teeth for grinding, pounding,
and crushing food.
Three pairs of salivary
glands—the parotid glands, the
sub maxillary glands, and the
sublingual glands—secrete
saliva into the mouth. The saliva
contains an enzyme called
amylase, which digests starch
molecules into smaller
molecules of the disaccharide
maltose.
The pharynx, or throat, is a funnelshaped tube connected to the posterior
end of the mouth. The pharynx is
responsible for the passing of masses
of chewed food from the mouth to the
esophagus. The pharynx also plays an
important role in the respiratory
system, as air from the nasal cavity
passes through the pharynx on its way
to the larynx and eventually the lungs.
Because the pharynx serves two
different functions, it contains a flap of
tissue known as the epiglottis that acts
as a switch to route food to the
esophagus and air to the larynx.
It is located at the
back of the throat
where oral and nasal
cavities join. Also it is
where swallowing
occurs.
The esophagus is a thickwalled muscular tube located
behind the windpipe that
extends through the neck and
chest to the stomach. The
bolus of food moves through
the esophagus by peristalsis: a
rhythmic series of muscular
contractions that propels the
bolus along. The contractions
are assisted by the pull of
gravity.
Cardiac sphincter is to
prevent a back flow of
materials back into the
esophagus. The cardiac
sphincter closes to allow the
food to stay within the
stomach so it can be digested.
Cardiac sphincter, working
with the pyloric sphincter
keeps the stomach content
from moving elsewhere.
The stomach is an expandable
pouch located high in the abdominal
cavity. Layers of stomach muscle
contract and churn the bolus of food
with gastric juices to form a soupy
liquid called chyme.
The stomach stores food and
prepares it for further digestion. In
addition, the stomach plays a role in
protein digestion. To protect the
stomach lining from the acid, a third
type of cell secretes mucus that lines
the stomach cavity. An
overabundance of acid due to mucus
failure may lead to an ulcer.
Pyloric sphincter is located at the
base of the stomach and is the
contracting ring of muscle which
guards the entrance of the to small
intestine.
It keeps the stomach shut at the far
end so that it has a chance to digest
proteins, then it opens and allows
the contents of the stomach, now
called chyme, to pass through the
pyloric sphincter and enter the small
intestine; the first section is called
the duodenum and it does the
majority of digestion and some
absorption.
It controls the emptying of chyme
into duodenum.
The duodenum is a short
portion of the small intestine
connecting it to the stomach. It
is about 10 inches (25 cm)
long, while the entire small
intestine measures about 20
feet (6.5 meters). The
duodenum also serves to
neutralize the acidity of the
chyme that exits the stomach,
an intermediate product in the
digestive process
The pancreas is a gland that
is located deep in the abdomen
between the stomach and the
spine (backbone) and is
surrounded by the liver, the
intestine, and other organs.
The role of the pancreas is to
make insulin, other hormones,
and pancreatic juices.
The gallbladder acts as a storage vessel
for bile produced by the liver. Bile is
produced by hepatocytes cells in the liver
and passes through the bile ducts to the
cystic duct .The walls of the duodenum
contain sensory receptors that monitor
the chemical makeup of chyme (partially
digested food) that passes through the
pyloric sphincter into the duodenum.
When these cells detect proteins or fats,
they respond by producing the hormone
cholecystokinin (CCK). CCK enters the
bloodstream and travels to the
gallbladder where it stimulates the
smooth muscle tissue in the walls of the
gallbladder.
The liver has an important function in
processing the products of human
digestion. For example, cells of the liver
remove excess glucose from the
bloodstream and convert the glucose to a
polymer called glycogen for storage.
The liver also functions in amino acid
metabolism. In a process called
deamination, it converts some amino
acids to compounds that can be used in
energy metabolism. In doing so, the liver
removes the amino groups from amino
acids and uses the amino groups to
produce urea. Mucus helps by lining the
digestive tract. This creates a barrier that
prevents infection, protects against acid
in the stomach, and moistens food,
making it easier to swallow.
Most absorption in the small intestine
occurs in the jejunum. The products of
digestion enter cells of the villi, move
across the cells, and enter blood vessels
called capillaries. Diffusion accounts for
the movement of many nutrients, but
active transport is responsible for the
movement of glucose and amino acids.
The products of fat digestion pass as
small droplets of fat into lacteals, which
are branches of the lymphatic system.
Absorption is completed in the final part
of the small intestine, the ileum.
Substances that have not been digested
or absorbed then pass into the large
intestine.
Villi, the singular of which is villus,
are finger-like projections in the
small intestine that help absorb food
more efficiently in the body. The
small intestine is an organ in the
body in which most digestion occurs.
Food entering into the body is
liquefied and partially digested in the
stomach. It then passes into the small
intestine. The villi are the parts that
absorb nutrients from food and pass
them into the bloodstream.
Villi are also covered with microvilli.
The appendix, also called
the vermiform appendix. The
appendix has no function in
modern humans; however, it
is believed to have been part
of the digestive system in our
primitive ancestors.
The large intestine is also known
as the colon. It is divided into
ascending, transverse, and
descending portions, each about
one foot in length. The colon's
chief functions are to absorb water
and to store, process, and eliminate
the residue following digestion and
absorption. The intestinal matter
remaining after water has been
reclaimed is known as feces.
The rectum is a chamber that
begins at the end of the large
intestine, immediately following
the sigmoid colon, and ends at the
anus. Ordinarily, the rectum is
empty because stool is stored
higher in the descending colon.
Eventually, the descending colon
becomes full, and stool passes into
the rectum, causing an urge to
move the bowels (defecate).
The anus is the opening at the far
end of the digestive tract through
which stool leaves the body. The
anus is formed partly from the
surface layers of the body,
including the skin, and partly from
the intestine. The anus is lined with
a continuation of the external skin.
A muscular ring (anal sphincter)
keeps the anus closed until the
person has a bowel movement.
Mechanical digestion is simply
the aspects of digestion achieved
through a mechanism or
movement. There are two basic
types of mechanical digestion.
Mastication: The first step when
it comes to digestion actually
begins as soon as food enters the
mouth. Mastication (chewing)
begins the process of breaking
down food into nutrients.
Peristalsis: Peristalsis is simply
the involuntary contractions
responsible for the movement of
food through the esophagus and
intestinal tracts.
Chemical digestion is much like it sounds –
those aspects of digestion achieved with the
application of chemicals to our food.
Digestive enzymes and water are responsible
for the breakdown of complex molecules
such as fats, proteins, and carbohydrates into
smaller molecules. These smaller molecules
can then be absorbed for use by cells.
The presence of these digestive enzymes
accelerates the digestion process, where
absence of these enzymes slows overall
reaction speed. Currently, there exist eight
digestive enzymes mainly responsible for
chemical digestion.
Amylase: Any of a group of enzymes that
catalyze the hydrolysis of starch to sugar to
produce carbohydrate derivatives.
Protease: Any of various enzymes,
including the proteinases and peptidases, that
catalyze the hydrolytic breakdown of
proteins.
Lipase: Any of a group of lipolytic enzymes
that cleave a fatty acid residue from the
glycerol residue in a neutral fat or a
phospholipid.
Nuclease: Any of a group of enzymes that
split nucleic acids into nucleotides and other
products.
You start chemically digesting large
carbohydrates, called starches, while you're
still chewing them. Enzymes in your saliva
called amylases break the bonds between
adjacent building block units that make up
starches. These building blocks, called
monosaccharides, are small, and your
intestine can absorb them. Your stomach
doesn't engage in much carbohydrate
digestion, but enzymes in the small intestine
finish the job, and after a short time in the
small intestine, carbohydrates break down
into nothing but monosaccharides.
Proteins, like carbohydrates, consist of
smaller building-block molecules. The
building blocks of proteins are called amino
acids. These are small enough that your
intestine can absorb them. You can't start
chemically digesting proteins in the mouth,
but significant protein digestion takes place
in the stomach. You complete protein
digestion in the small intestine, and from
there, you absorb the resultant amino acids.
Unlike carbohydrates and proteins, fats
aren't chains of smaller building blocks.
Instead, they consist of a "backbone" made
up of a molecule of glycerol, which is similar
to alcohol. Attached to the glycerol backbone
are three long molecules consisting of mostly
carbon and hydrogen; these are fatty acids.
Enzymes in your small intestine break two of
the fatty acids away from the glycerol,
leaving a single fatty acid and glycerol
attached to one another. This is called a
monoglyceride, and you absorb it and the two
free fatty acids into the body.
Making Bile
Bile is a thick, green-yellow fluid that the liver produces to help digest food,
especially fat, as it passes from the stomach to the intestines. This fluid is made in the
liver, but is stored in a nearby sac called the gallbladder
Removing Toxins from the Blood
All of the blood in the body will eventually pass through the liver. This is important
because the liver needs to pull out any bad things in the blood, such as toxins, and
remove them from the body.
Building Proteins
Proteins are everywhere in the body, and need to be constantly produced. The liver is
in charge of building many kinds of proteins that the body uses every day. For
instance, there are many proteins produced by the liver that are responsible for blood
clotting. When the liver is damaged, sometimes the body isn't able to clot blood
effectively.
The pancreas serves two roles in the human body. One function is to produce
enzymes that break our food down small enough to be absorbed into our body. The
second function is to produce the hormones insulin and glucagon. The pancreas can
develop disorders and diseases that effect both functions. It manufactures and
secretes digestive enzymes such as amylase, which digests starch. It also produces
lipase, which breaks down fats, and trypsin, a protein processor. The pancreas creates
and secretes insulin, glucagon and other hormones. Insulin and glucagon are
especially important for the maintenance of blood sugar, as insulin lowers the blood
sugar and glucagon increases the blood sugar according to the body's needs.
Portions of your digestive tract are
suspended within the peritoneal cavity
by sheets of serous membrane that
connect the parietal peritoneum with
the visceral peritoneum. These
mesenteries are double sheets of
peritoneal membrane. Mesenteries also
stabilize the positions of the attached
organs and prevent your intestines
from becoming entangled during
digestive movements or sudden
changes in body position.
Mucus helps by lining the
digestive tract. This creates a
barrier that prevents infection,
protects against acid in the
stomach, and moistens food,
making it easier to swallow.
Components in saliva help keep the
pH in your mouth between 6.5 and 7
so that the enzyme salivary amylase
can start to break down carbohydrates.
The enzymes that help digest food in
the stomach, such as pepsin, work best
at a pH around 2, while those that
function in the intestines, including
peptidases and maltase, work best at a
pH around 7.5.
The E. Coli, to simply put it, is a
bacterium that resides within the tracts
of the digestive system. Every humans
and animals actually have this bacteria
and it even aids the body to stand
against harmful microorganisms and
also assist in the production of vitamin
K. Those are the so-called “good
bacteria” in the body. But then again,
the bad bacteria also exist to oppose
the good ones. These are the types of
E. Coli that causes disease. There are
too many types of E. Coli bacteria but
the most important and common ones
will be discussed that usually cause
harm inside the human body.
Ulcer — an open sore on the lining
of the stomach (gastric ulcer) or
duodenum (duodenal ulcer). Peptic
ulcers occur in areas that come in
contact with digestive juices from
the stomach. They may be caused or
worsened by prolonged use of overthe-counter, non steroidal antiinflammatory medications
(NSAIDs) such as aspirin or
ibuprofen, or by a bacterial infection
(H. pylori). (H. pylori infection is
usually acquired from contaminated
food and water and through person
to person spread.)
Heartburn — an
uncomfortable feeling of
burning and warmth occurring
in waves rising up behind the
breastbone toward the neck. It is
usually due to gas troesophageal
reflux disease (GERD), the rise
of stomach acid back up into the
esophagus.
Good bye! Wish you learn something useful and take
photos during this trip!