The Digestive Process
The main purpose of the Digestive system is to break down food and absorb
nutrients. There are two basic divisions to the digestive system, these are the
gastrointestinal (GI) tract, also known as the alimentary canal, and the
accesory digestive organs. Your mouth, pharynx, esophagus, stomach, small
intestine and large intestine compose the GI tract, and your teeth, tongue,
salivary glands, liver, gall bladder and pancreas are accessory organs.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 GI tract 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 GI tract 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.
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).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.
Digestive System Glossary:
anus - the opening at the end of the digestive system from
which feces (waste) exits the body.
appendix - a small sac located on
ascending colon - the part of the
large intestine that run upwards; it is located after the cecum.
bile - a digestive chemical that is
produced in the liver, stored in the gall bladder, and secreted into the small
cecum - the first part of the large
intestine; the appendix is connected to the cecum.
chyme - food in the stomach that is
partly digested and mixed with stomach acids. Chyme goes on to the small
intestine for further digestion.
descending colon - the part of the
large intestine that run downwards after the transverse colon and before the
duodenum - the first part of the
small intestine; it is C-shaped and runs from the stomach to the jejunum.
epiglottis is the flap of cartilage lying behind the
tongue and in front of the entrance to the larynx (voice box). At rest, the
epiglottis is upright and allows air to pass through the larynx and into the
rest of the respiratory system. During swallowing, it folds back to cover the
entrance to the larynx, preventing food and drink from entering the
esophagus - the long tube between the mouth and the stomach. It
uses rhythmic muscle movements (called peristalsis) to force food from the
throat into the stomach.
gall bladder - a small, sac-like
organ located by the duodenum. It stores and releases bile (a digestive
chemical which is produced in the liver) into the small intestine.
ileum - the last part of the small intestine before the large intestine begins.
jejunum - the long, coiled
mid-section of the small intestine; it is between the duodenum and the ileum.
liver - a large organ located above
and in front of the stomach. It filters toxins from the blood, and makes bile
(which breaks down fats) and some blood proteins.
omentum is an apronlike double fold
of fatty membrane that hangs down in front of the intestines. It contains blood
vessels, nerves, lymph vessels and lymph nodes. It acts as a storage for fat
and also may limit the spread of infection in the abdominal cavity.
pancreas - an enzyme-producing gland located below the stomach and above
the intestines. Enzymes from the pancreas help in the digestion of
carbohydrates, fats and proteins in the small intestine.
peristalsis - rhythmic muscle movements that force food in the esophagus
from the throat into the stomach. Peristalsis is involuntary - you cannot
control it. It is also what allows you to eat and drink while upside-down.
rectum - the lower part of the large intestine, where feces are stored
before they are excreted.
salivary glands - glands located in the mouth that produce saliva.
Saliva contains enzymes that break down carbohydrates (starch) into smaller
sigmoid colon - the part of the large intestine between the descending
colon and the rectum.
stomach - a sack-like, muscular organ that is attached to the esophagus.
Both chemical and mechanical digestion takes place in the stomach. When food
enters the stomach, it is churned in a bath of acids and enzymes.
transverse colon - the part of the large intestine that runs
horizontally across the abdomen.