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Chemical Digestion
Stomach
The pyloric sphincter at the bottom of the
stomach governs the passage of food out of the
stomach into the small intestine.About 10
inches down the esophagus, the swallowed food
or bolus is now fairly well minced and turned
into a pulpy mass as it passes into the stomach.
The function of the stomach is best described as
a food processing unit (similar to one you may
have in your kitchen) and a storage cistern. The
stomach is both chemical and mechanical.
Various chemicals in the stomach like the
digestive enzymes pepsin, rennin, and lipase
interact to break down the food. In addition,
hydrochloric acid creates suitable environment
for the enzymes and assists in the digestion.
Also, the watery mucus provides a protective
lining for the muscular walls of the stomach so
it will not be digested by the acid or enzymes.
The mechanical action of the muscles in the
stomach constrict and relax in a continuous motion blending, whipping, and stirring the stomach's contents into
chyme, a pulpy substance that can be handled by the small intestine.
Small intestine
The small intestine is the longest organ of the digestive tract. It is divided up indiscriminately into three
sections: the duodenum, the jejunum, and the ilium.
Duodenum
This is the place where the ultimate destruction of food
digestion reaches its completion and where the acidity
of chyme is nullified. Enzymes are secreted by the
walls of the duodenum and unite with the pancreatic
enzymes in the duodenum.
Jejunum
Peristalsis pushes the nutrient liquid out of the
duodenum into the first reaches of the jejunum. A
greater number of villi, microscopic, hair like
structures, begin to absorb substances from the digested
contents of the small intestine, turns them into thin
watery liquid and starts them on their way to other parts
of the body.
Ilium
This is the place which is about a third of the small intestine. The greatest number of the estimated five or six
million villi in the small intestine are found along the ilium making it the main absorption locale of the
gastrointestinal tract.
The Liver, Gallbladder, and Pancreas
Legitimately, these three organs lie outside of the
gastrointestinal tract. Nevertheless, digestive fluids from all three meet like intersections of a railway track at
the common bile duct, and their movement from there into the duodenum is controlled by a sphincter muscle.
The pancreas is a producer of digestive enzymes. The gallbladder is a small reservoir for bile. The liver
reproduces nutrients so that they can be used for cell-rebuilding and energy.
Large Intestine
There is a merger between the ilium and the
cecum, the first section of the large intestine.
What the cecum primarily inherits is water.
What the large intestine essentially does,
other than act as a passageway for removal
of body wastes, is to act as a provisional
reservoir for water. There are no villi in the
large intestine and peristalsis is much less
forceful than in the small intestine. As water
is absorbed, the contents of the large
intestine change from a watery liquid and
are compressed into semisolid feces. Nerve
endings in the large intestine signal the brain
that it is time for a bowel movement. The
fecal material moves through the colon
down to several remaining inches known as
the rectum and out through the anus an
opening controlled by the outlet valves of
the large intestine.
Enzymes and Other Secretions
Site of Enzyme Enzyme
Origin
Nutrient It Breaks
Down
Salivary Glands Salivary Amylase
Carbohydrates-sugars Simple Sugars
Mouth
Gastric glands
Pepsin
Proteins
Amino Acids
Stomach
Liver
Bile
Fats/Lipids
Emulsified Fats
Small Intestine
Small Intestine Maltase, Lactase,
Sucrase
Carbohydrates
Simple sugars
Small Intestine
Pancreas
Proteins, Fats/Lipids,
Carbohydrates
Amino acids, Glycerol/Fatty
Acids, Simple Sugars
Small Intestine
Trypsin, Lipase,
Amylase
Product Of Enzyme Action
Place of
Enzyme Action
Mechanical Digestion
Mechanical Digestion begins in the mouth, where the saliva, teeth, and tongue all play an important
role in this digestive process and it ends in the stomach.
Mouth
The MOUTH contains the tongue which is covered with tiny projecting papillae through which are
conveyed sensations of taste and touch; the teeth; and the salivary glands, which secrete saliva.
The process of digestion starts in the mouth. Food is masticated (chewed) by the teeth, moistened by
the saliva, which contains important chemical substances for changing it, and rolled by the tongue. It
is then pushed backward by the tongue into
Pharynx
The PHARYNX is a funnel-shaped opening which is a continuation of the mouth. The food then
passes down the smallest taste, smell, and anticipation of food sends signals to the brain. The brain
in turn sends messages to a system of salivary glands. Saliva is essentially made up of water and
begins to soften up the food so it can pass more smoothly down the throat. Besides water there is
also a very special substance, an enzyme called ptyalin, whose main task is to breakdown the food
into simpler forms.
Esophagus
This is a very elastic, muscular tube about eight to ten inches (18 to 25 cm) long. The food is forced
onward by the involuntary contractions of the muscles in the esophagus. It passes from the
esophagus into the stomach.
Movements
After ingestion and mastication, the food particles move from the mouth into the pharynx, then into
the esophagus. This movement is deglutition, or swallowing. Mixing movements occur in the stomach
as a result of smooth muscle contraction. These repetitive contractions usually occur in small
segments of the GI tract and mix the food particles with enzymes and other fluids. The movements
that propel the food particles through the GI tract are called peristalsis.
Peristalsis
This mechanical action has to do with sets of muscles that cooperate to move both liquid and solid
food along the digestive tract. In other word, it pushes food along your esophagus, stomach, and
intestine... Gravitational pull is lessened in a sense when food enters the esophagus because of
peristalsis. Peristalsis helps a person to swallow lying down or even standing on their head.
Peristalsis has another essential task besides assisting in the movement of food through the body. It
also helps to knead, agitate, and pound the solid residue that is left after the teeth or those without
teeth, the gums, have done their best. These are rhythmic waves of contractions that move the food
particles through the various regions in which mechanical and chemical digestion takes place.
Digestive
System
The organ system includes the
gastrointestinal tract (GI tract) and
its accessory organs. The digestive
system processes food into
molecules that can be absorbed
and utilized by the cells of the
body. Food is broken down, bit by
bit, until the molecules are small
enough to be absorbed and the
waste products are eliminated. The
gastrointestinal (GI) tract, also
called the digestive tract,
alimentary canal, or gut, consists of
a long continuous tube that
extends from the mouth to the
anus. It includes the following
regions:








mouth
pharynx
esophagus
stomach
small intestine
large intestine
rectum
anus
The tongue and teeth are
accessory structures located in the
mouth. The salivary glands, liver,
gallbladder, and pancreas are
major accessory organs that have
a role in digestion. These organs
secrete fluids into the GI tract.
Food undergoes three types of
processes in the body:
 digestion
 absorption
 elimination
Digestion and absorption occur in
the GI tract. After the nutrients are
absorbed, they are available to all
cells in the body and are utilized by
the body cells in metabolism.