Histology of the gastrointestinal tract Flashcards
Stomach histology: Mucosa
Surface mucous cells
Located in pits. Secrete an alkaline substance called VISIBLE (more viscous, thick) mucus that protects the stomach from damage by abrasion and stomach acid.
Covers surface of stomach to prevent stomach from digesting itself.
Stomach histology: mucosa
Mucous neck cells:
Located in the isthmus/neck region of the glands (below surface mucous cells). Secrete “normal mucus under vagal stimulation.
Stomach histology: mucosa
Parietal cells
Located in the glands. Below mucous neck cells. Secrete intrinsic factor (required for utilization of B12) / HCl (stomach acid).**
Contain Intracellular canaliculi. This increases surface area tremendously. Stimulated by parasympathetic innervation and paracrine release of histamine and gastrin to secrete their product.
Large, round in shape with spherical nucleus, very eosinophilic cytoplasmic (pink).
Tubulovesicular system (membrane storage system) made of series of membranes made of proton pumps that can be inserted into the walls of intracellular canaliculus to increase surface area.
Stomach histology: mucosa
Chief cells
Located deep in glands. Below parietal cells. These are what secrete the digestive enzymes: Pepsinogen and Gastric Lipase ***
Basophilic (blue), very abundant.
Stomach histology: mucosa
Enteroendocrine cells
Located in glands. Hormone producing cells. Made of cells that stimulate gastric function, for example: G cells. G cells secrete gastrin.
Stomach histology: mucosa
Stem cells
Found in both pits in glands. Undergo mitosis to produce all other epithelial cell types. They are undifferentiated.
Stomach histology: Muscularis externa
Made of 3 layers, what makes the pyloric sphincter?
Outer longitudinal layer
Middle circular layer (thickens at pylorus to form pyloric sphincter)
Inner oblique layer
Small intestine histology: mucosa
Interesting features
Plicae (fold) circulares (circular) - circular folds in the walls of the intestine, covered by mucosa, with submucosa core. Increases surface area.
Villi: Large finger-like projections. (macro-villi not microvilli)
Between villi, you have intestinal crypts. These are pits extending below surface. (we call them crypts in small intestine, and pits in stomach).
Small intestine histology: mucosa
Goblet Cells
Interspersed between the enterocytes (simple columnar absorptive cells)
Small intestine histology: mucosa
Paneth Cells
Only found in base of crypts, only in small intestine.** Key identifying characteristic
Vivid red stain from large eosinophilic granules, contain lysozymes, phospholipase A2, and defensins. Play a role in innate immunity.
Small intestine histology: mucosa
M (microfold) cells
Located in mucosa of ileum overlying the Peyer’s patches
Have a pocket formed of invaginated basolateral membrane that contains lymphocytes, macrophages, dendritic cells
Capture intestinal microorganisms and antigens and transfer them to the immune cells that they shelter
Small intestine histology: mucosa
Lacteals
Special lymph capillaries in middle of a villus that absorb fats and carry them to the venous system via thoracic duct.
Small intestine histology: submucosa
Brunner’s glands
in DUODENUM only. These are large mucous glands that secrete alkaline mucus that neutralizes acidic chyme coming from stomach.
If you see villi and mucus glands, you are in duodenum.
Small intestine histology: submucosa
Peyer’s patches
Mucosa-associated lymphoid tissue (MALT). AGgregations of lymph nodules, present in terminal part of ILEUM. They are huge purple dots of B-lymphocytes.
Extra: if you see villi and crypts but no brunner’s glands or peyer’s patches, then you are just in small intestine and not duodenum/ileum.
Large intestine histology
contain crypts but no villi. The appendix, an extension of the cecum, has abundant lymph nodules but it is not the ileum bc no villi.
