This post contains many high yield images that help to identify some of the identifying features of the ileum, the third portion of the small intestines. If you haven't already, be sure to read A Histology Tour of the GI Tract- Small Intestines Overview before continuing...
Functions of the Ileum
Villi have absorptive function
Microvilli increase the surface area of absorption
Muscularis externa helps in churning food particles i.e peristalsis
Serosa is supportive and protective in function
Peyer's patches have an immunologic function
Histology
HELPFUL IDENTIFYING FEATURES:
Finger-like villi lined by simple columnar epithelium.
Villi rich in goblet cells.
Crypts of lieberkuhn present.
Mucosa containing Peyer’s patches
HISTOLOGY LAYERS(From the inner mucosal (luminal) surface to external surface)
MUCOSA lined by simple columnar epithelium with fine microvilli, mucous secreting goblet cells. Formed into large folds or finger like projections called villi.
LAMINA PROPRIA contain tubular intestinal glands or crypts of lieberkuhn and numerous aggregations of lymphatic nodules called ‘Peyer’s patches’.
Crypts of lieberkuhn consists of following cells:
Stem cells: active, undifferentiated cells found at the base of lamina propria.
Goblet cells: secrete mucus.
Enteroendocrine cells: present above the stem cells. Also called as ‘argentaffin cells’ since they are stained by silver salts. Belong to APUD (amine precursor uptake decarboxylase) system.
Paneth cells: zymogenic cells, producing digestive enzymes and lysozymes.
MUSCULARIS MUCOSA/INTERNA this layer consists of disrupted circular muscle layers.
SUBMUCOSA made up of loose areolar connective tissue. Contains some lymphoid tissue which is migrated from lamina propria.
MUSCULARIS EXTERNA consists of outer longitudinal and inner circular muscle fibers with parasympathetic ganglion cells of myenteric plexus sandwiched between the two layers.
SEROSA outer most layer made up of few connective tissue cells and fibers, covered by mesothelium of visceral peritoneum
Continue browsing through the high yield (or simply very pretty) images below to acquaint yourself with "normal" histology findings in the ileum.
Now that you have familiarized yourself with the ileum, you can continue learning about the identifying features for each organ by clicking on the respective post in the GI- Small & Large intestines chapter. Next up, the colon!