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The Digestive System
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Organs of the Digestive System
 Two main groups
 Alimentary canal
or GI tract
 Accessory
digestive organs
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Organs of the Alimentary Canal
 Mouth
 Pharynx
 Esophagus
 Stomach
 Small intestine
 Large intestine
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Accessory Digestive Organs
 Salivary glands
 Teeth
 Pancreas
 Liver
 Gall bladder
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Mouth (Oral Cavity)
 Lips – sense temp.
and texture; protect
mouth
 Hard palate and
Soft palate – form
the roof
 Uvula – fleshy
projection at the
back of the soft
palate
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Mouth (Oral Cavity)
 Tonsils
palatine tonsils - on
either side of the
back of the mouth
lingual tonsils– at
the back of the
tongue
both play a role in
the immune system
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Digestive Processes in the Mouth
 mastication (chewing) of food
 mixing of masticated food with saliva
(secreted by salivary glands)
 saliva contains enzymes that begin the
digestion of carbohydrates
 initiation of “deglutition” (swallowing) by
the tongue
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Pharynx (throat)
 food and air share this
passageway
 muscular tube that
moves food into the
esophagus
 when we swallow food,
a flap of tissue known
as the “epiglottis”
covers the trachea
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Esophagus
 muscular tube that runs
from pharynx to stomach
through the diaphragm
 moves food by
peristalsis (slow
rhythmic contractions)
 cardiac sphincter (lower
esophageal sphincter)
 group of muscles, at the
bottom of the esophagus,
that contracts and closes
the entrance to the
stomach when food is
present – this prevents
The Stomach
 pouch-like organ in the left hypochondriac region
of the abdominal cavity
 regions of the stomach:
 cardiac region – portion closest to the heart
 fundus – upper rounded portion
 body – middle portion
 pylorus – narrow bottom portion
 pyloric sphincter – circular muscle at the base of
the stomach which controls the emptying of the
stomach’s contents into the small intestine
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Stomach Anatomy
• the lining of the
stomach is thick
and has many
folds called “rugae”
• as the stomach fills
up, the wall distends
and the folds
disappear
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Digestive Processes in the Stomach
 food is mixed with gastric juice (contains
hydrochloric acid and enzymes)
pepsin begins to break down protein
 muscle movements of the stomach form a
semifluid mass called “chyme” (processed
food)
 muscles move chyme, in small batches,
into the small intestine
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Small Intestine
 it is about 20 feet long
from stomach to large
intestine
 lined with villi (tiny, onecell-thick fingerlike
projections with
capillaries) through
which digested nutrients
are absorbed into the
bloodstream
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Subdivisions of the Small Intestine
“Dogs Just Itch!”
 Duodenum
 10 inches long
 chyme mixes with bile (digests fat), pancreatic
juice (digests starch, proteins, and fat) and
intestinal juice (digests sugars)
 Jejunum
 8 feet long
 Ileum
 connects small intestine to large intestine
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Subdivisions of the Small Intestine
“Dogs Just Itch!”
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Large Intestine
 about 5 feet long
 forms a rectangle around the tightly
packed small intestine
 waste products usually remain in the
large intestine from 12 – 24 hours
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Large Intestine
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Subdivisions of the Large Intestine
 Cecum
 saclike first part of the large intestine
 has 3 openings: one from the ileum into cecum,
one from the cecum into the colon, and one from
the cecum into the appendix
 Appendix is filled with lymphatic tissue and can
become inflamed (appendicitis)
 Water and necessary substances are absorbed
into the bloodstream and feces is formed
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Subdivisions of the Large Intestine
 Colon
 ascending colon:
extends upward
 transverse colon:
extends across
 descending
colon: extends
downward,
where it
connects to the
sigmoid colon
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Subdivisions of the Large Intestine
 Sigmoid Colon
 S-shaped body that goes across the pelvis
to the middle of the sacrum, where it
connects to the rectum
 Rectum
 attaches to the anal canal
 sphincter muscles of the anus open during
the release of feces from the body
(defecation)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings