Small Intestinal Crypt of Lieberkühn.

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Module Name: crypt
Module Title: Small Intestinal Crypt of Lieberkühn.
Image Info: Electron micrograph taken by Lisa Roberts, 10,000X (?) magnification.
Created by: Lynn Bry
Date: Dec 12th, 1996.


Key points: Paneth cell | granule | lumen | undifferentiated crypt stem cell | lamina propria | nucleus |

Introduction: Electron micrograph of a mouse small intestinal crypt. The small intestine contains large finger-like projections (villi). A one-cell thick epithelium overlies each villus. The epithelium regenerates itself thorughout life, and serves not only as the initial site for processing nutrients absorbed from the lumen, but also acts as a barrier to prevent microbes in the lumen from crossing into the body.

The base of intestinal villi extends into the crypts of Lieberkühn (one is shown here). Within the crypts multipotent crypt stem cells divide through life, giving rise to the epithelial lineages. Cells differentiate as they leave the crypt for the villus surface. Migration continues until cells are lost from the tip of a villus into the intestinal lumen. The exceptions are the intestinal Paneth cells which reside at the base of the crypts.


Paneth_cell: Differentiated crypt Paneth cell. Unlike other lineages, Paneth cells migrate to the crypt base. They have a long life-span of ~28 days. Paneth cells are noted for their prominent secretory appartus. Granules are readily visulaized using a variety of stains including the Phloxine-Tartrazine histochemical stain. The granules contain digestive enzymes (phospholipases, peptidases), mucins and anti-microbial factors such as lysozyme, the defensin-related cryptdins and IgA taken up from lamina propria plasma cells. As all products enter the crypt lumen, these cells provide a primary defense to microbial colonization in this sensitive regions of the small intestine. Only mammalian herbivores and omnivores have Paneth cells.

fibroblast: Lamina propria fibroblast. These cells form a 'basket network' arround the crypt base and are believed to play an important role in regulating the differentiation and proliferation of nearby epithelial stem cells.

granule: Paneth cell secretory granule. Paneth cell granules exhibit a typical electron dense core surrounded by an electron-lucent halo. Lysozyme, cryptdins andother secreted factors localize to the electron dense areas.

lamina_propria: The lamina propria contains many important cell types and structures. Lacteals/lymphatics and vessels within each villus transport nutrients to the portal circulation. Fribroblasts and other mesenchymal cells provide stucture and support for the overlying epithelium. Large numbers of lymphoid cells circulate within the lamina propria. These cells represent part of the gut mucosal defense to microbial translocation across the epithelial barrier.

lumen: Crypt lumen. Many modulatory factors are released into the crypt lumen, possibly to control the differentiation programs of the epithelial stem cells. Paneth cells release a phospholipase A2 (enhancing factor) that affects the binding of epidermal growth factor (EGF) to its receptor.

nucleus: Stem cell nucleus. Mitoses are frequent in the crypt epithelium due to the contiunous proliferation and differentiation of the epithelial stem cells.

undifferentiated_crypt_stem_cell: The epithelial crypt stem cells give rise to all epithelial cell lineages. These lineages include the villus-associated absorptive enterocytes, mucin-secreting goblet cells, enteroendocrine cells, and the crypt-associated Paneth cells. Committed precursor cells are believed to arise from a single multi-potent stem cell. Differentiation of the four primary cell types is completed at the crypt-villus junction. Villus associated cells continue their migration along the villus surface. These cells undergo apoptosis near the villus tip and are subsequently lost after 3-5 days in the mouse.

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