Structural and mechanical architecture of the intestinal villi and crypts in the rat intestine: integrative reevaluation from ultrastructural analysis

Abstract

The ultrastructure of the rat intestinal interstitium was analyzed from the viewpoint of mechanical dynamics to stabilize the intestinal villi, crypts and mucosal folds. In the rat, the small intestine lacks circular folds, but the large intestine possesses spiral folds. The intestinal villi, the largest in the duodenum, decreased in size in the jejunum and ileum successively, and were absent in the large intestine. The intestinal interstitium consisted of lamina propria mucosae (LPM) and tela submucosa (TSM) separated by muscularis mucosae (MM), the LPM was subdivided into an upper part within the villi and a lower part among the crypts in the small intestine. The light microscopic density of interstitium in the intestinal wall was lowest in the upper LPM, moderately dense in the lower LPM and highest in the TSM, and that among the intestinal region was highest in the duodenum and decreased successively in the jejunum and ileum. In the large intestine, the TSM bulged to form spiral folds with very low density. The intestinal epithelium in the villi possessed wide intercellular spaces and that in the crypts had closed intercellular spaces. At electron microscopic level, the upper and lower LPM contained subepithelial supportive meshwork that consisted of collagen fibrils and myofibroblast processes. The lower LPM and TSM contained conspicuous bundles of collagen fibrils and, in addition, TSM contained minor populations of scattered collagen fibrils near the smooth muscle layer (SML). The diameter of collagen fibrils was the largest in the bundles of TSM, and decreased from the duodenum through the jejunum and ileum to the large intestine. On the basis of these observations, we hypothesize that the intestinal villi are mechanically stabilized by the balance between the expansive interstitial pressure and inward pull by the subepithelial supportive meshwork. This hypothesis explains the hitherto neglected fact that the intestinal epithelium possesses wide intercellular spaces only in the villi, and accounts for the counterforce against the perpendicular smooth muscle cells, which are supposed to contract the intestinal villi.

Trichostatin A protects against intestinal injury in rats with acute liver failure

“…As the intestinal villi are gradually descending from duodenum to ileum in sized and absent in colon, 25 the laminal surface is decreased. The more the intestinal epithelial barrier damaged, the severer the endotoxemia.…”

The villi contribute to the mechanics in the guinea pig small intestine

“…Although the villi exhibit different dimensions and configurations in the duodenum, jejunum and ileum, in the rat small intestine they are roughly ridge-like in shape running in circumferential direction (Hosoyamada and Sakai, 2005). The stress-strain distribution mainly reflects the elastic properties of the intestinal wall.…”

“…The mucosa of the small intestine is arranged into two fundamental structures, villi as projections into the lumen and crypts. From a mechanical point of view, the homeostasis of intestinal villi and crypts are thought to be maintained by the balance of expanding forces derived from capillary and interstitial pressures on the one hand, and contracting forces produced by interstitial cells and extracellular matrices on the other (Hosoyamada and Sakai, 2005). However, there is yet no information available on the contribution of the villi on the passive biomechanical properties of the intestine.…”

Non-animal models of epithelial barriers (skin, intestine and lung) in research, industrial applications and regulatory toxicology

“…These vital functions are maintained by a diverse set of cell types and a unique tissue architecture. The intestinal mucosa is characterized by the presence of villi, which constitute the anatomical and functional unit for nutrient and drug absorption, and can be further subdivided into the epithelial layer (which constitutes the intestinal barrier), the lamina propria (collagen matrix containing blood and lymphatic vessels) and the muscularis mucosae (Carr et al, 1981;Hosoyamada and Sakai, 2005;Nelson, 2004). The intestinal epithelium is mostly made up of absorptive enterocytes that transport macromolecules, ions and water.…”