Mechanical components of rat intestinal villi as revealed by ultrastructural analysis with special reference to the axial smooth muscle cells in the villi

Abstract

The ultrastructure of the rat intestinal interstitium with regard to the mechanical components was analyzed from a functional viewpoint utilizing serial horizontal as well as longitudinal sections through the lamina propria mucosae, including both villi and crypts. The axial smooth muscle cells in the villi (villus-axial SMs) exhibited different configurations at various levels of the wall. They were separated from the voluminous fluid-filled spaces by sheet-like processes of fibroblasts in the upper part of the intravillous interstitium, formed a sheet around the central lymphatics, and were covered by the sheet-like processes of fibroblasts in the lower part of the intravillous interstitium. These villus-axial SMs were poorly developed and associated with the lymphatic walls in the upper part of the pericryptal interstitium; they were tapered and connected to microtendons composed of fascicles of longitudinal collagen fibrils in the lower part of pericryptal interstitium. At the apical termination, the villus-axial SMs were connected to myofibloblasts, which sent off many processes into the subepithelial meshwork layer of fine cell processes and extracellular matrices. The villus-axial SMs possibly develop longitudinal tension against the intravillous hydraulic pressure developing from the transepithelial absorption through the intestinal epithelium.

Determination of Villous Rigidity in the Distal Ileum of the Possum (Trichosurus vulpecula)

“…Conversely, a degree of laxity at the point of union of the base of the villus with the adjacent mucosa would allow villous shafts to pivot with respect to the plane of the underlying mucosa and thus to accentuate crowding within the concavity between adjacent mucosal folds. Given the turgor of the interstitial tissue within the shafts of villi [11] that results from a combination of hydrostatic distension by absorbed fluids and opposing circumferential tension of the collagen fibres of the villous lamina propria [12], it seems unlikely that villous shafts would possess a high degree of flexibility. However, given the differences in the dispositions and densities of collagen fibres in the subepithelial network of the villous lamina propria from that in the pericryptal lamina propria [12], the junction between the two sites would likely allow a degree of pivoting.…”

“…Given the turgor of the interstitial tissue within the shafts of villi [11] that results from a combination of hydrostatic distension by absorbed fluids and opposing circumferential tension of the collagen fibres of the villous lamina propria [12], it seems unlikely that villous shafts would possess a high degree of flexibility. However, given the differences in the dispositions and densities of collagen fibres in the subepithelial network of the villous lamina propria from that in the pericryptal lamina propria [12], the junction between the two sites would likely allow a degree of pivoting. However to date, no work has been carried out to determine the flexibility of the villous shafts or the laxity of their bases during lumen flow.…”

Are the precapillary sphincters and metarterioles universal components of the microcirculation? An historical review

“…In the other 13 kinds of tissues, the precapillary sphincters were not observed at all with TEM, SEM-vc or SEM-rem. Our own observations of the microvasculature in the lung [71], kidney [72–74] and intestine [75, 76] did not show any indication of precapillary sphincters.…”

Structural organization of pulmonary veins in the rat lung, with special emphasis on the musculature consisting of cardiac and smooth muscles

“…We have improved tissue processing to better visualize the vasculature and interstitium of various viscera, including the renal glomerulus (Sakai and Kriz 1987;Inkyo-Hayasaka et al 1996;Ichimura et al 2007) renal peritubular basement membrane (Hijikata and Sakai 1991), renal arteries Sakai 1993, 1994;Sakai and Kobayashi 1992), hepatic interstitium (Hosoyamada et al 2000), periductal interstitium of exocrine glands (Hosoyamada and Sakai 2003), and intestinal interstitium (Hosoyamada and Sakai 2005;Hosoyamada and Sakai 2007). We have also investigated the ultrastructure of the pulmonary arteries (Sasaki et al 1995), and the developmental processes of the pulmonary alveolar interstitium (Yamada et al 2005).…”