This image shows a cross
section of the ileum that has been straightened out. The ileum has the same general
organization as the other regions of the small intestine. The innermost layer
is the mucosa
(Mu), consisting of a simple columnar epithelium supported
by a layer of loose connective tissue called the lamina propria. Finger-like extensions
of the mucosa, called villi
(Vi), extend into the lumen and increase the surface area
for absorption. The bases of the villi are surrounded by the openings of intestinal
glands, also called crypts
of Lieberkuhn (CL), which are branched tubular glands that
extend all the way to the muscularis
mucosae (MM), the thin layer of smooth
muscle that marks the boundary between the mucosa and the underlying submucosa
(SMu). The latter is a layer of loose connective tissue
containing ganglia of the parasympathetic branch of the autonomic nervous system,
called Meissner's plexi.
The most characteristic feature of the ileum is the presence of large lymphoid
nodules, called Peyers
patches (PP), located in the submucosa, but often breaching
the muscularis mucosae to penetrate into the lamina propria of the mucosa.
Peyers patches have
light-staining germinal centers surrounded by darker staining layers of lymphoid
cells. The next layer is the muscularis
externa (ME), which consists of two layers of smooth muscle
- an inner circumferential layer and an outer longitudinal layer - separated by
a thin layer of loose connective
tissue (CT). The outermost layer is the serosa
(Se),
which consists of little more than a simple squamous epithelium of mesothelial
cells.
