Text of OVERVIEW The Digestive System. Digestive System The digestive system is also called the...
OVERVIEW The Digestive System
Digestive System The digestive system is also called the
gastrointestinal (GI) system. 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 tissues.
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 mouth.
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 pancreas.
In the digestive system, food is changed into usable nutrients
by mechanical action and chemicals called enzymes.
Proteins are changed to amino acids; Carbohydrates are changed
into simple SUGARS like glucose. Fats are changed into FATTY acids
The nondigestable parts of the food consumed are moved along
into the intestines, and are finally excreted from the body as
Several organs contribute to the function of the digestive
system and many disease conditions affect them.
The Mouth The digestive process begins in the mouth where food
is chewed so it can be easily swallowed. The tongue is a skeletal
muscle covered with taste buds.
The tongue and the teeth work together to chew the food
mastication, the tongue then propels the food backward to the
pharynx. The tongue also helps in SPEECH.
The mouth also houses the SALIVARY glands which secrets a
digestive enyzme. The pharynx connects the mouth to the esophagus,
the pharynx serves as a PASSAGEWAY for both 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 ESOPHAGUS.
Stomach The stomach is a strong hollow elastic MUSCULAR organ
with circular muscles at each end. These CIRCULAR 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 stomach. 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 DESTORY the 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.
INTESTINES 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:
Parts of the intestine The first 10 12 inches is the duodenum.
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
This absorption is possible because the small intestine is
covered with many projections called villi. Each tiny villi
contains blood and lymph capillaries. 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 intestine.
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
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 upward.
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 colon.
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 movement) The
process of defecation is under conscious control despite the reflex
action. If the urge to defecate is ignored, may result in
Diseases Gastritis 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.
Diseases Constipation The inability to expell the contents of
the rectum. Colitis an inflammatory disease of the colon.
Hemorrhoids enlarged veins in the rectum. Appendicitis inflammation
of the appendix.
Diseases Cholecystitis 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.