Crypts of lieberkiihn

More detailed knowledge of the mechanisms of iron absorption from the gastrointestinal tract of mammals has advanced by leaps and bounds in the last few years, with the cloning of key participants at both the apical and basolateral faces of the mucosal endothelial cells. The extraordinarily far-sighted contribution of William Crosby and Marcel Conrad, nearly 40 years ago (Conrad and Crosby, 1963 Crosby, 1963), reminded us of the key role of body iron status in determining the level at which iron absorption will be set within the cells of the crypts of Lieberkiihn when they differentiate and move up to the villus tips to play their key role in... 

Ulcerative colitis is confined to the colon and rectum and affects primarily the mucosa and the submucosa. The primary lesion occurs in the crypts of the mucosa (crypts of Lieberkiihn) in the form of a crypt abscess. 

The concept that the scolex of adult cestodes is generally non-penetrative has been shown not to hold for species such as Echinococcus granulosus and E. multilocularis, where the scolex penetrates the crypts of Lieberkiihn and, occasionally, even the lamina propria (Fig. 9.5) often resulting in a complete breakdown of the mucosal epithelium. These species can be regarded as both tissue and lumenal parasites. That the scolex contact is close is reflected in the fact that anti-Echinococcus antibodies appear in dog sera 14 days post-infection (p.i.) (368). It is likely, however, that in many cestodes the scolex contact is more superficial and breakdown of the mucosa may not occur, especially in those species which undergo diurnal migration - see Chapter 9. 

Between the villi are pits, the crypts of Lieberkiihn, containing undifferentiated cells which move up to the tip of the villus, maturing in shape and function as they progress. They function for a few days and are then shed the entire epithelial population is replaced every four to seven days. 

The origin and fate of the intestinal epithelial cells have been traced using radioautography. The absorptive cell proliferates in the crypts of Lieberkiihn. The new cells migrate toward the apex of the villi where they are extruded. Cellular proliferation and cellular extrusion are not rigidly linked for example, irradiation blocks cellular proliferation but doesn t affect cellular extrusion, and the villi atrophy. In sprue the reverse occurs cellular proliferation persists, but cellular extrusion seems to be accelerated. 

The small intestine in nicotinic acid deficiency becomes red, its walls become thickened, and it is covered by grey cyst-like structures which are produced by distension of the crypts of Lieberkiihn. The fluid content of these cysts is the normal secretion of the crypts (Hertzenberg ). The mucosa of the colon may also be infiltrated with various leucocytes, particularly lymphocytes, plasma cells, and eosinophiles (Denton ). 

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