The esophagus is a muscular tube about 25 cm
(10 inches) long. It is the passageway between the
pharynx and the stomach. By means of waves of
muscular contractions (peristalsis), food is pushed
along this tube to the stomach. When peristalsis
is reversed, vomiting occurs.
The stomach is a saccular enlargement of the
gastrointestinal tube, connecting the lower end of
the esophagus and the first portion of the small
intestine (duodenum). It lies in the left upper
quadrant of the abdomen. Muscular rings, or
sphincters, at each end of the stomach form valves
to close off the stomach and to prevent its con-
tents from escaping in either direction while they
are being mixed by peristaltic muscular contrac-
tions of the stomach wall. The sphincter at the
esophageal end is the cardiac sphincter; at the
duodenal end it is the pyloric sphincter.
The stomach acts as an initial storehouse for
swallowed material and helps in the chemical
breakdown of food substances. Small glands in
the wall of the stomach secrete gastric juice, the
principal components of which are hydrochloric
acid and pepsinogen. Hydrochloric acid activates
pepsin from pepsinogen, kills bacteria that enter
the stomach, inhibits the digestive action of
ptyalin, and helps regulate the opening and clos-
ing of the pyloric sphincter. The action of pepsin
is confined to protein, which it splits. The stomach
is half-empty within 1 hour of a normal meal and
completely empty in 6 hours.
Most food absorption takes place in the small
intestine. There is little food absorption in the
stomach. One exception is alcohol, which is ab-
sorbed directly through the stomach wall. For this
reason intoxication happens quickly when alcohol
is taken on an empty stomach.
The stomach and intestines are enclosed in the
the space between the
diaphragm and the pelvis. This cavity is lined with
serous membrane, the PERITONEUM. The
peritoneum covers the intestines and the organs
and, by secreting a serous fluid, prevents friction
between adjacent organs. The MESENTERY
(double folds of peritoneum) extends from the
cavity walls to the organs of the abdominal cavity,
suspending them in position and carrying blood
vessels to the organs.
The small intestine is a muscular, convoluted
(coiled) tube, about 7 meters (23 feet) long and
attached to the posterior abdominal wall by its
mesentery. The mesentery is gathered together like
a folding fan, permitting coiling of the intestine,
allowing this long organ to be contained in a
relatively small space.
The small intestine is divided into three contin-
uous parts: the duodenum, jejunum, and ileum.
It receives digestive juices from three accessory
organs of digestion: the pancreas, liver, and
The DUODENUM is about 25 cm (10 inches)
long and forms a C-shaped curve around the head
of the pancreas, posterior to the liver. It is lined
with a mucous membrane that contains small
glands. These glands secrete intestinal juices con-
taining the enzymes carbohydrate, peptidase, and
The JEJUNUM is the middle part of the small
intestine and is about 2.5 meters (7.5 feet) long.
Its enzymes continue the digestive process.
The ILEUM is the last and longest part of the
small intestine. Most of the absorption of food
occurs in the ileum where fingerlike projections
(villi) provide a large absorption surface. After
ingestion it takes 20 minutes to 2 hours for the
first portion of the food to pass through the small
intestine to the beginning of the large intestine.
The large intestine is so called because it is
larger in diameter than the small intestine. It is
considerably shorter, however, being about 1.5
meters (5 feet) long. It is divided into three distinct
parts: the cecum, colon, and rectum.
The unabsorbed food or waste material passes
through the CECUM into the COLON. The
cecum is a pouch at the beginning of the large in-
testine, located in the lower right portion of the
abdominal cavity. Twelve hours after the meal,
most of the waste material passes through the
colon slowly, building in mass and reaching the
rectum 24 hours after the food is ingested.
The APPENDIX, a long narrow tube with a
blind end, is an outpouching of the cecum located
near the junction of the ileum and the cecum. It
has no known function but frequently becomes
infected and an inflammation known as appen-
The RECTUM is 12.5 cm (5 inches) long and
follows the contour of the sacrum and coccyx until