tract, or
a lim e n ta ry ca n a l.
The GI tract contains food
from the time it is eaten until it is digested and ab-
sorbed or eliminated from the body. Extending from the
mouth to the anus, the GI tract is about 5-7 meters long
(16.5-23 ft). It is divided into specialized sections re-
ferred to as digestive organs, which include the mouth,
pharynx, esophagus, stomach, small intestine, and large
intestine (Figure 14.1).
In addition to the digestive organs of the GI tract,
there are several accessory digestive organs, including
the salivary glands, liver, pancreas, and gall bladder. These
accessory organs secrete substances into the GI tract or
perform other functions.
In sum, the digestive system performs several vital
functions:
In g e stio n .
Taking food into the mouth
Secretion.
Releasing water, acid, buffers, and enzymes
into the lumen of the GI tract
M ix in g a n d p ro p u lsio n .
Churning and pushing food
through the GI tract
D ig estio n .
Physically and chemically breaking down food
A b so rp tio n .
Passing digested products from the GI tract
into the blood and lymph
D efeca tio n .
Eliminating feces from the GI tract
THIE
pLANNER^
Left lobe
of liver/*
Right lobe
of liver
Pancreas
Gallbladder
Liver
receives, metabolizes, and stores nutrients absorbed
from the small intestine. It secretes bile that breaks down
large lipid globules.
Gallbladder
stores bile secreted by the
liver.
Pancreas
(behind stomach) secretes sodium
bicarbonate and enzymes that break down food into amino
acids, lipids, and simple carbohydrates.
Small intestine
absorbs sugars, lipids, peptides,
water, ions, and vitamins from food. It also secretes
hormones that acts on other digestive organs.
Large intestine
absorbs water, ions,
and vitamins. Resident bacteria break
down remaining carbohydrates and
proteins (bilirubin). Chyme becomes
semi-solid
feces
, which get expelled
through the
anus
.
Let's Journey Through the Digestive System 401
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