DUODENAL BULB AND MUCOSAL SURFACE OF DUODENUM
The mucosa of the widened first portion of the duodenum, known also as the duodenal ampulla (cap, bulb), is relatively flat and smooth except for a few small longitudinal folds. Except for the smooth duodenal ampulla, the mucosal surface of the duodenum, which in living subjects is reddish in color, is lined with villi, giving the small intestines their velvety appearance. The mucosa of the distal duodenum is nearly identical to the small intestine with circular folds (of Kerckring) projecting into the lumen. These folds, which considerably increase the surface area of the intestine, begin in the region of the superior duodenal flexure, increasing in number and elevation in the more distal parts of the duodenum. They do not always form complete circles along the entire intestinal wall, because some are semicircular or crescent shaped, whereas others branch out to connect with adjacent folds. Very often they deviate from their circular pattern and pursue a more spiral course. The circular folds are large macroscopic structures and include mucosa and submucosa in their core. The more superficial layers of the duodenum, the muscularis externa and adventitia, are not included in the circular folds.
Approximately halfway down the posteromedial aspect of
the descending part of the duodenum, a distance of approximately 8.5 to 10 cm
from the pylorus, is located the major duodenal papilla, also known as
the papilla (of Vater). This is where the common bile duct and
the major pancreatic duct (of Wirsung) open into the duodenum. The
common bile duct approaches the duodenum within the enfolding hepatoduodenal
ligament of the lesser omentum and continues inferiorly in the groove between
the descending portion of the duodenum and the pancreas. The terminal part of
the common bile duct produces a slight but perceptible longitudinal impression
in the posteromedial duodenal wall known as the longitudinal fold of the
duodenum. This fold usually ends at the papilla but may occasionally
continue for a short distance beyond the papilla in the form of the so-called
frenulum. Small hoodlike folds at the top of the papilla protect the mouth of
the combined bile duct and pancreatic duct. A small, wartlike, and generally
less distinct second papilla, the minor duodenal papilla, is situated
about 2.5 cm above and slightly medial to the major papilla. It serves as an opening for the minor
pancreatic duct (of Santorini).
The duodenal ampulla, varying in form, size, position,
and orientation, appears in an anteroposterior radiograph as a triangle, with
its base at the pylorus and its tip pointing toward the superior flexure of the
duodenum. The duodenum’s longitudinal folds, as well as the circular folds in
the lower parts of the duodenum, can be visualized radiographically if a barium
meal of appropriate quantity and consistency is given. In such a relief picture
of the mucosa, the region of the major duodenal papilla occasionally appears as
a small, roundish filling defect. When the papilla is enlarged in the form of a
small diverticulum, the contrast medium may sometimes enter the terminal
portions of the bile and pancreatic ducts, with the result that on the x-ray,
this area l oks like the shape of a molar tooth with two roots.
