Fundamentals of Anatomy and Physiology

390

The Small Intestine

The major portion of absorption and digestion occurs in the
small intestine. It is approximately 21 feet in length and
averages 1 inch in diameter (Figure 16-12). The small
intestine is divided into three portions. First is the
duodenum, which is the shortest part and is about 10 inches
long. The duodenum originates at the pyloric sphincter
and joins the second portion, the jejunum (jee-JOO-num).
The jejunum is about 8 feet long and extends to the third
part, the ileum (ILL-ee-um), which measures 12 feet and
joins the large intestine at the ileocecal (ill-ee-oh-SEE-
kal) valve (sphincter).
The mucosa of the small intestine contains many pits
lined with glandular epithelium. These pits are known as the
intestinal glands or crypts of Lieberkuhn (KRIPTZ of
LEE-ber-koon). They secrete the intestinal digestive en-
zymes that supplement the bulk of the digestive enzymes

Chapter 16

secreted by the liver and the pancreas. The submucosa of

the duodenum contains numerous Brunner’s glands,

now called duodenal glands, which secrete an alkaline

mucus. Additional mucus is secreted by goblet cells. This

mucus protects the walls of the small intestine from being

di-gested by enzymes and neutralizes the acid found in the

chyme (KIGHM). Chyme is the term used to describe the

digested, viscous, semifluid contents of the intestine.

Approximately 80% of all absorption of nutrients

(simple sugars, amino acids, fatty acids, water, vita-mins,

and minerals) occurs in the small intestine. The anatomic

structure of the small intestine is highly spe-cialized for this

function (Figure 16-13). First of all, the tract is 21 feet

long. Second, an even larger surface for absorption of

nutrients is provided by the structure of the walls of the

tract, which are thrown into a series of folds called plicae

(PLYE-kee). Third, the mucosal coat is transformed into

projections called villi, which

Liver

Gallbladder

Pylorus

Duodenum

Mesentery

Ascending

colon

Cecum

Appendix

Ileum

Figure 16- 12 Structures of the small intestine.

Esophagus

Cardiac

Fundus

Body

Pyloric^

sphincter

Pancreas

Jejunum

(^) ®
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