Page 406 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

362 seCtion iii Gastrointestinal ` gastrointestinal—anatomy Gastrointestinal ` gastrointestinal—anatomy

Digestive tract Layers of gut wall A (inside to outside—MSMS):
anatomy ƒ Mucosa—epithelium, lamina propria, muscularis mucosa
ƒ Submucosa—includes Submucosal nerve plexus (Meissner), Secretes fluid
ƒ Muscularis externa—includes Myenteric nerve plexus (Auerbach), Motility
ƒ Serosa (when intraperitoneal), adventitia (when retroperitoneal)
Ulcers can extend into submucosa, inner or outer muscular layer. Erosions are in mucosa only.
Frequency of basal electric rhythm (slow waves), which originate in the interstitial cells of Cajal:
ƒ Stomach—3 waves/min
ƒ Duodenum—12 waves/min
ƒ Ileum—8–9 waves/min

A
Mucosa
Epithelium
Lamina propria Tunica mucosa
Muscularis mucosa
Mesentery
Tunica submucosa
Submucosa
Vein Submucosal gland
Artery
Lymph vessel
Lumen
Submucosal nerve
plexus (Meissner)
Muscularis
Inner circular layer
Myenteric nerve plexus Tunica muscularis
(Auerbach)
Outer longitudinal layer Tunica serosa
Serosa (peritoneum)

Digestive tract histology
Esophagus Nonkeratinized stratified squamous epithelium. Upper 1/3, striated muscle; middle and lower 2/3
smooth muscle, with some overlap at the transition.

Stomach Gastric glands A .
Duodenum Villi B and microvilli  absorptive surface. Brunner glands (HCO -secreting cells of submucosa)
−
3
and crypts of Lieberkühn (contain stem cells that replace enterocytes/goblet cells and Paneth cells
that secrete defensins, lysozyme, and TNF).
Jejunum Villi, crypts of Lieberkühn, and plicae circulares (also present in distal duodenum) C .
Ileum Peyer patches (arrow in D; lymphoid aggregates in lamina propria, submucosa), plicae circulares
(proximal ileum), and crypts of Lieberkühn. Largest number of goblet cells in the small intestine.
Colon Crypts of Lieberkühn with abundant goblet cells, but no villi E .
A B C D E

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