This post contains many high yield images that help to identify some of the identifying features of the duodenum. If you haven't already, be sure to read A Histology Tour of the GI Tract- Small Intestines Overview before continuing...
After food has traveled through and been partially digested in the stomach, the next stop is the duodenum. The duodenum is the first (and shortest) segment of small intestine, about 25 cm long.
Functions of the Duodenum
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
Brunner’s glands secrete alkaline fluid rich in HCO3‾
HELPFUL IDENTIFYING FEATURES:
**Brunner’s glands present in submucosa
Numerous villi (leaf-shaped)
Crypts of Lieberkuhn present
Brunner's glands present in the submucosa are a key feature to telling you are in the duodenum!
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. Plica circularis is a mucosal fold with a core of submucosa
LAMINA PROPRIA contain tubular intestinal glands or crypts of lieberkuhn. 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 circular muscle layers.
SUBMUCOSA made up of loose areolar connective tissue. Presence of numerous mucus secreting Brunner’s glands
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 duodenum.
Now that you have familiarized yourself with the duodenum, 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 Jejunum!