A In Depth Look at
Digestion
By: Deneale K. Williams
From page 476 and forward of the text book we
learn that ingestion is just another
word for eating. Digestion is the
breakdown of the food small enough for the body to absorb, into what we know as
molecules. Absorption is when the
food is transferred into the blood stream. This is the uptake of small nutrient
molecules by cell lining in the digestive tract. Elimination is just like it sounds, the body getting rid of waste.
The disposal of unwanted, unneeded materials left over from food. These are the
four stages of food processing.
Now as you know, to begin the entire
process, you must begin by what? Chewing. This is considered the mechanical
beginning of digestion.
Once the food hits the stomach it begins
with chemical digestion, the breakdown of food by digestive enzymes.
Dismantling food molecules is necessary
for two reasons: they must be broken down for the cells to absorb, they are
currently too large. Some is dismantled and used to build proteins. Your body does not directly use the
protein that you eat but instead dismantles it and uses the pieces (amino
acids) to build its own new proteins.
Chemical digestion
happens by way of hydrolysis. These are chemical reactions by large biological
molecules by the addition of water molecules, which require enzymes. Food molecules that are polymers,
such as carbohydrates and proteins, are broken down via chemical digestion into
monomers.
Did you know that
there are different digestive compartments? It is true. “The simplest type of
digestion occurs within a cellular organelle. In this process, a cell engulfs
food by phagocytosis, forming a vacuole. This food vacuole then fuses with a
lysosome containing enzymes, forming a digestive compartment. As food is
digested, small food molecules pass through the vacuole membrane into the
cytoplasm and nourish the cell.”
We as humans, and
the earthworm have a digestive tube with two separate openings our mouth at one
end and an anus at the other end. Such a tube is called an alimentary canal, or
digestive tract. The food we eat moves in just one direction through
specialized regions that digest and absorb nutrients in a stepwise fashion.
This adaptation allows for much more efficient food processing. Just like an
assembly line. Undigested wastes are eliminated from the alimentary canal as
feces by way of the anus.
“The human digestive system consists of an alimentary canal and several
accessory organs (salivary glands,
pancreas, liver, and gallbladder). The accessory organs secrete digestive
chemicals into the alimentary canal via ducts (thin tubes). The human
alimentary canal totals about nine meters (thirty feet) in length. Such a long
tube fits within a human body because it folds back and forth over itself with
many switchbacks.”
“The alimentary canal is divided into specialized digestive organs along
its length: mouth (oral cavity) → pharynx
→ esophagus → stomach → small intestine → large intestine (colon and rectum) →
anus.”
But let us not forget where it all begins! With our mouth, our salivary glands, our tongue, our palette and
our lovely and favorite taste buds. And did you know, the more wear and tear
you put on those lovely teeth, you
can wear them out? Of course, you do! You go to the Dentist! But did you know
that chemical digestion begins in the mouth? It does with the salivary glands who help to begin the
process after you have started chewing.
From there your pharynx and esophagus work together.
Your pharynx is located in your throat
is an intersection of the pathways for swallowing
and breathing. The pharynx connects the mouth to the esophagus (part of the digestive system). But the pharynx also
opens to the trachea, or windpipe,
which leads to the lungs (part of the respiratory system). When you’re not
swallowing, the trachea entrance is open and you can breathe, which is also
located by your voice box. Air
enters the larynx (also called the voice box), flows past the vocal chords,
through the trachea, and to your lungs. Men generally have larger larynxes and
therefore more prominent Adam’s apples formed by cartilage on the outside of
the larynx.
This is how the
Heimlich maneuver was created, when the food has been allowed to go down the
wrong pipe, wind forces it out, when chocking occurs.
Your esophagus is a muscular tube that
connects the pharynx to the stomach. Your esophagus moves food by peristalsis,
alternating waves of muscular contraction and relaxation that squeeze the food
ball along the esophagus.
The stomach is a large organ that can
sustain you for several hours. The stomach can hold more than half a gallon of
food or drink.
“The cells lining the stomach’s interior secrete a digestive fluid
called gastric juice. Gastric juice
is made up of a strong acid, digestive enzymes, and mucus. The acid in gastric
juice is hydrochloric acid, and it is concentrated enough to dissolve iron
nails. (You read that
right! Your own body could actually dissolve iron nails!!) Gastric juice
also contains pepsin, an enzyme that
breaks proteins into smaller pieces.”
“When the stomach
mixes up all of the gastric juices it is called chyme. At the downstream end of the stomach, a sphincter (a ring of muscle) works like a drawstring to close the
stomach off, holding the chyme there for about two to six hours. The chyme leaves
the stomach for the small intestine one squirt at a time. Continued
contractions of stomach muscles after the stomach is empty causes the “stomach
growling” that lets everyone know you are hungry.”
Gastric juice can
be harmful, if you have ever heard of heartburn. This is a backflow up the
esophagus. It can be quite annoying and even painful, and it can even degrade
your esophagus over time, if not tended to. You may have heard it referred to
as acid reflux or even GERD.
The small intestine is not small in length,
it is small in diameter. It is usually about twenty feet long. It is two-point
cm across, the large intestine is five cm across. The small intestine is
necessary for digestion and absorption of nutrients into the bloodstream. Normally
it takes approximately six hours to pass into the small intestine. The small
intestine takes over with an arsenal of enzymes that dismantle the food
molecules into smaller molecules. These enzymes are mixed with chyme in the
first twenty-five cm or so of the small intestine, the region called the duodenum.
“The duodenum receives digestive juices from the pancreas, liver, gallbladder, and the intestinal lining. The
pancreas is a large gland that secretes pancreatic juice into the duodenum via
a duct. Pancreatic juice neutralizes the stomach acid that enters the duodenum,
and it contains enzymes that aid in digestion. As peristalsis propels the mix
along the small intestine, these enzymes contribute to the breakdown of food
molecules.”
“Bile is a juice produced by
the liver, stored in the gallbladder, and secreted through a duct into the
duodenum. Bile contains salts that break up fats into small droplets that are
more susceptible to dismantling by digestive
enzymes.”
If you have ever thrown up to the point that you have ever emptied your
stomach to the point that you have puked yellow and tasted the nastiest taste
ever, you have herby tasted bile. You had better be wrinkling your nose right
now!
Five feet in length, the large
intestine is shorter than the small intestine. But as I have explained
earlier, you now know, it is wider.
Nearby the large intestine, is the appendix.
If you know what is at the end of the book, what is it? The appendix. And what
do many people get removed? Their appendixes, and their gall bladders. I have
neither one. It is not a good thing to be without though, let me tell you. It
causes your digestive tract to work differently no matter what they try and
tell you.
“The appendix contains white blood cells that make minor contributions
to the immune system. If the junction between the appendix and the large
intestine becomes blocked, appendicitis—a bacterial infection of the
appendix—may result. Emergency surgery is usually required to remove the
appendix and prevent the spread of infection.”
The main portion
of the large intestine is the colon.
The primary function of the colon is to absorb water from the alimentary canal.
About ninety percent of the water it contains is absorbed back into your blood
and tissue fluids, with the small intestine reclaiming much of the water and
the colon finishing the job.
The rectum, the last six inches on the
large intestine stores feces until they can be eliminated. Contractions of the
colon and the rectum create the urge to defecate. Two rectal sphincters, one
voluntary and the other involuntary, regulate the opening of the anus. When the voluntary sphincter is
relaxed, contractions of the rectum expel feces.
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