680
UNIT FIVE
Parts of the Small Intestine
The small intestine, shown in
f
gures 17.31
and
17.32
and
in reference plates 12 and 18, consists of three portions: the
duodenum, the jejunum, and the ileum.
The
duodenum
(du
o-de
num), about 25 centimeters
long and 5 centimeters in diameter, lies posterior to the pari-
etal peritoneum (retroperitoneal). It is the shortest and most
F xed portion of the small intestine. The duodenum follows a
C-shaped path as it passes anterior to the right kidney and the
upper three lumbar vertebrae.
The remainder of the small intestine is mobile and lies
free in the peritoneal cavity. The proximal two-F fths of this
portion is the
jejunum
(je
˘-joo
num), and the remainder is the
ileum
(il
e-um). There is no distinct separation between the
jejunum and ileum, but the diameter of the jejunum is usually
greater, and its wall is thicker, more vascular, and more active
than that of the ileum. The ileum has more lymph nodules
(Peyer’s patches) and a higher bacterial population.
The jejunum and ileum are suspended from the poste-
rior abdominal wall by a double-layered fold of peritoneum
called
mesentery
(mes
en-ter
e)
(f g. 17.33)
. The mesentery
supports the blood vessels, nerves, and lymphatic vessels
that supply the intestinal wall.
Stomach
Small intestine
FIGURE 17.32
Radiograph showing abnormal small intestine containing a radiopaque substance that the patient ingested.
Stomach
Jejunum
Duodenum
Ascending colon
Mesentery
Appendix
Cecum
Ileum
FIGURE 17.31
The three parts of the small intestine are the
duodenum, the jejunum, and the ileum.
previous page 710 David Shier Hole's Human Anatomy and Physiology 2010 read online next page 712 David Shier Hole's Human Anatomy and Physiology 2010 read online Home Toggle text on/off