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The Digestive System
Digestive System
The digestive system is
also called the
gastrointestinal (GI)
This system is
responsible for the
physical and chemical
breakdown of food so it
can be taken into the
blood stream and used
by all body cells and
Many organs work
together to form the
digestive system.
 The alimentary/GI
tract canal or tract is a
long muscular tube
that begins at the
Included in the
alimentary tract is the
oral cavity, pharynx,
esophagus, stomach
and intestines.
The accessory organs
in this system are the
salivary glands,
tongue, teeth, liver,
gallbladder and
In the digestive
system, food is
changed into usable
nutrients by
mechanical action
and chemicals called
Proteins are changed
to amino acids;
Carbohydrates are
changed into simple
 Fats are changed into
FATTY acids and
The nondigestable
parts of the food
consumed are moved
along into the
intestines, and are
finally excreted from
the body as feces.
Several organs
contribute to the
function of the
digestive system and
many disease
conditions affect
The Mouth
The digestive process
begins in the mouth
where food is chewed
so it can be easily
 The tongue is a
skeletal muscle
covered with taste
 The
tongue and the teeth work together to
chew the food mastication, the tongue
then propels the food backward to the
 The tongue also helps in SPEECH.
The mouth also houses
the SALIVARY glands
which secrets a digestive
The pharynx connects
the mouth to the
esophagus, the pharynx
serves as a
food and air.
Food goes into the
esophagus, air goes
into the trachea on its
way to the lungs.
The Esophagus
The esophagus is a tube
10 to 12 inches in length
that carries the food to
the stomach.
Muscular contractions
call peristalic waves
which move the food
through the entire
digestive tract begin in
The stomach is a strong
hollow elastic
MUSCULAR organ with
circular muscles at each
muscles called sphincters
hold the food in the
STOMACH until it is
throughly mixed with
digestive enzymes.
When there is no food
in the stomach, folds
called RUGAE form in
the mucous
membrane of the
 These many folds
allow for the stomach
to enlarge as it fills
with food.
Millions of GASTRIC
GLANDS in the stomach
secrete a gastric juice.
This gastric juice
contains; pepsin,
necessary for the
breakdown of PROTEIN;
hydrochloric acid,
necessary to dissolve
minerals found in the
foods and provides the
stomach a strong
ACID environment
which is needed to
bacteria and
microorganisms that
enter the stomach in
the food we eat.
 The
stomach cells also produce the
intrinsic factor which helps the body
absorb vitamin B12.
 The action of the gastric juice on the food,
assisted by the churning of the stomach
produces a semi liquid called Chyme.
 When
the chyme is ready to leave the
stomach, the pyloric sphincter opens and
allows the food to enter the duodenum.
 The contraction and relaxation of the
smooth muscles called peristalsis move
the food along the alimentary tract.
The small intestine is
a coiled tube 20 to 25
feet in length and one
inch in diameter. The
small intestine is
divided into three
Parts of the intestine
The first 10 – 12
inches is the
 The next 8 to 10 feet
is called the jejunum.
 The final 12 feet or so
is called the ileum.
The small intestine
contains many
intestinal glands
which produce
intestinal juice.
 In addition bile from
the liver and
pancreatic juices from
the pancreas empty
into the duodenum.
 Bile,
manufactured by the liver is needed
for the digestion of fat. The pancreatic
juice contains strong enzymes that
continue the digestion of protein, act on
starch and digest fat. The combined
action of bile, pancreatic juice, and
intestinal juice complete the breakdown of
food which can then be absorbed by the
blood stream.
This absorption is
possible because the
small intestine is
covered with many
projections called villi.
 Each tiny villi contains
blood and lymph
 The usable nutrients
pass through the villi
into the blood stream.
The lymph capillaries
absorb some of the
fat ingested in the
food eaten. The
portion of food that is
undigestible passes
into the large
Accessory organs
 During
the process of digestion, the liver, a
large organ in the upper right of the
abdomen, produces bile which is stored in
the gallbladder. The gallbladder, a small
muscular sac, releases bile when the
chyme passes into the duodenum.
The bile contains
mineral salts which
may crystallize and
form gall stones,
causing obstruction of
the bile flow.
The liver
The liver does several
other vital functions
besides producing
bile: Removal of
poisons absorbed in
the intestines, storage
of excess sugar in a
form called glycogen,
storage of certain
Formation of
antibodies, production
of certain proteins
necessary for blood
clotting, removal of
waste products from
protein called urea.
The pancreas
The pancreas in
addition to producing
digestive juices, also
produces insulin, a
hormone secreted
directly into the blood.
 Insulin is necessary
for metabolism or
burning of
The Large Intestine
The large intestine or
colon is about 5 feet
long and 2 inches in
diameter. The large
intestine begins at the
lower right corner of
the abdomen and is
called the ascending
colon as it continues
Large intestine
Then it lies across the
upper abdomen which
is called the
transverse colon, and
continues down the
left side where it is
called the descending
At the junction of the
large and small
intestine is a valve
called the ileocecal
valve. Just below this
valve is the appendix
which has no
digestive function.
The appendix
The appendix is a
fingerlike projection
containing a blind sac
which may become
irritated and inflamed.
 As the descending
colon reaches the
pelvis, it makes a “S”
shaped bend, known
as the sigmoid colon.
The final portion of
the sigmoid extends
to form the 7-8inch
Rectum, which opens
exteriorly to the anus.
 The function of the
large intestine is
concerned with water
absorption, bacterial
action and formation
of feces.
 As
the digested food enters the colon it
contains a great deal of liquid. In the
colon the water absorption and bacterial
action turn this liquid into a semisolid form
and gas.
 Feces
is the term given to this mass,
sometimes called stool.
 The peristalsis which is moving the
undigested food along continues until it
enters the rectum.
 When
the rectum becomes distended, a
defecation reflex is trigger alloing the
emptying of the bowels. (Bowel
 The process of defecation is under
conscious control despite the reflex action.
 If the urge to defecate is ignored, may
result in constipation.
– irritation and inflammation of
the stomach lining. (gastric Flu)
 Ulcers – a lesions or erosion of the lining
of the stomach or small intestines
 Hepatitis – an inflammation of the liver.
 Cirrhosis – a chronic disease of the liver
causing liver cells to be replaced with scar
tissue which is non functioning.
 Gastritis
– The inability to expell the
contents of the rectum.
 Colitis – an inflammatory disease of the
 Hemorrhoids – enlarged veins in the
 Appendicitis – inflammation of the
 Constipation
or cholelithiasis – inflamation
of the gall bladder often caused by the
formation of crystallized mineral salts.
 Tumors which may either be malignant
(cancers) or benign (Non cancerous) may
also affect the digestive system.
 Cholecystitis