Digestion is the breakdown of food into simpler molecules that
can be absorbed by the body. The digestive system is actually
a long hollow tube called the gastrointestinal tract, or GI
tract. The digestive system includes the mouth, pharynx, esophagus,
stomach, small intestine, and large intestine. Several major
glands include the salivary glands, the pancreas, and the liver.
The first task of the digestive system is to break down food
into a fine pulp (mechanical digestion). When the food is physical
broken down, digestive chemicals break the food down into small
molecules (chemical digestion).
The mouth is the organ in which the process of digestion begins.
It starts the process of mechanical digestion by grinding the
food with teeth. Also in the mouth, an enzyme called salivary
amylase begins to break down long starch molecules into maltose.
Once the food is ready to be swallowed it is gathered into a
ball called a bolus and sends to the part of the bolus called
Once in the pharynx, the bolus next passes down the esophagus.
The bolus is moved down the esophagus by rhythmic muscles contracts
called peristalsis. At the end of the esophagus is a thick ring
of a muscle called a sphincter which allows food to enter the
stomach but not from the stomach back into the esophagus.
Once the food enters the stomach it is mixed with the digestive
juices. The stomach produces stomach acid; hydrochloric acid,
and pepsin. Stomach acid activates the pepsin that digests protein
into smaller proteins. Proteins are long chains of amino acids
that are essential for cell growth and repair.
Next, from the stomach the food moves into the small intestine
where it continues to be digested by enzymes produced in the
pancreas. In the small intestine, the pancreas empties digestive
juices that break down carbohydrates, fats, and protein. The
liver produces bile that is stored in the gallbladder between
meals and emptied into the small intestine. The small intestine
is where most of the nutrients are absorbed and thus is the
most important organ in the digestive system.
The undigested materials continue to the large intestine where
the remaining water is absorbed and eventually the waste material
is expelled through the rectum. Also, fats (lipids) are molecules
that are stored for future energy uses mainly because they are
difficult to digest.
Drawings of the human digestive system
Our models of the digestive system
Chemistry review and food
Food indicator tests
- Benedicts solution
- Burrets solution
- Sudan IV
Tests of own food
Fast food diets
Molecular models of food
|The main components of the digestive system
are the esophagus, stomach, small intestine, large intestine,
liver, gallbladder, pancreas, and bile duct
The three types of foods are proteins, carbohydrates,
Food is broken down into simpler forms which then can
be used by the body
A protein is a chain of amino acids which help with cell
growth and repair
Carbohydrates give the cells energy. They are composed
of long chains of sugars
Enzymes help to speed up reactions and are important
in the digestive system
Digestion takes place in the stomach, small intestine,
large intestine, liver, gallbladder, pancreas, ducts
Certain foods take longer to digest – fats are
the longest – often stored as energy.
Lipase, pepsin, maltase, carboxypeptidase, and amylase
are enzymes that break down food
Digestion is the process in which food and liquid are
broken down into their smallest parts so that the body
can use them
L2.p2A Describe how organisms
sustain life by obtaining, transporting, transforming, releasing,
matter and energy. (prerequisite)
B2.3d Identify the general functions of the major systems
of the human body (digestion, respiration,
reproduction, circulation, excretion, protection from disease,
and movement, control, and coordination)
and describe ways that these systems interact with each other
B2.2f Explain the role of enzymes and other
proteins in biochemical functions (e.g., the protein hemoglobin
carries oxygen in some organisms, digestive enzymes, and hormones).
B2.2g Propose how moving an organism to a new
environment may infl uence it ability to survive and predict
the possible impact of this type of transfer.