The main function of the digestive system is to break down food into mole-
cules small enough for the body to absorb. The nutrients are absorbed in the
body and used for energy. Our digestive system goes through eight basic
How long is the average digestive system?
-Mark off 3 inches (7 cm) of string to represent your mouth.
-Add 10 inches (25 cm) for your esophagus.
-Add 6 inches (15 cm) for your stomach.
-Add 18 feet (5.5 m) for your small intestine.
-Add 5 feet (1.5 m) more for your large intestine.
! Ingestion The first function of the digestive system is ingestion, or the intake of food.
The mouth is responsible for this function, as it is the orifice through which
all food enters the body. The mouth and stomach are also responsible for
the storage of food as it is waiting to be digested. This storage capacity al-
lows the body to eat only a few times each day and to ingest more food than
it can process at one time.
! ! !
Once food has been reduced to its building blocks, it is ready for the body
to absorb. Absorption begins in the stomach with simple molecules like wa-
ter and alcohol being absorbed directly into the bloodstream. Most absorp-
tion takes place in the walls of the small intestine, which are densely folded
to maximize the surface area in contact with digested food. Small blood and
lymphatic vessels in the intestinal wall pick up the molecules and carry
them to the rest of the body. The large intestine is also involved in the ab-
sorption of water and vitamins B and K before feces leave the body. ! Excretion The final function of the digestive system is the excretion of waste in a
process known as defecation. Defecation removes indigestible substances
from the body so that they do not accumulate inside the gut. The timing of
defecation is controlled voluntarily by the conscious part of the brain, but
must be accomplished on a regular basis to prevent a backup of indigestible
! Digestion refers to the process that breaks foods down into their constituent
carbohydrates, proteins and fats, and then further deconstructs each nutrient
into its component molecules. Muscles lining the walls of the digestive sys-
tem contract to mix food with enzymes while pushing it through the diges-
tive system. Cells and organs produce enzymes that break down the carbo-
hydrates, proteins and fats. Finally, special structures in the intestine absorb
nutrients. While movement, chemical breakdown and absorption are diges-
tive functions, the steps of digestion are defined by their unique roles in the
mouth, stomach, small intestine and large intestine.
Digestion begins the minute you put food in your mouth. Saliva softens
food so it's easier for the teeth to crush and grind. Taking the time to prop-
erly chew food is important because smaller pieces of food allow the stom-
ach to work more efficiently. Saliva also contains salivary amylase, which
is an enzyme that starts breaking down...