Morphogenesis of intestinal villi. I. Scanning electron microscopy of the duodenal epithelium of the developing chick embryo

Abstract

Development of villi in the duodenum of the chick was studied in stages ranging from 11 days of incubation to one week after hatching. Formation of definitive villi is preceded by development of a set of previllous ridges that run lengthwise along the duodenum. The first set of 16 previllous ridges (Set I) is complete by about 13 days of incubation; all ridges in the set are fairly uniform and proceed through their subsequent development in synchrony. Previllous ridges in Set I fold into a highly regular zigzag pattern between 14 and 16 days of incubation. Definitive villi develop from Set I ridges beginning at about 17 days when populations of distinct cells appear on the crests of the ridges between angles in the zigzag folds. Cells in these populations lack the rounded appearance of cells seen in earlier stages; their apical surfaces are densely covered with microvilli. A second set of villi (Set 11) develops at about 16 days of incubation when about 16 rows of tongue-like flaps erupt between the previllous ridges of Set I. At hatching, Set I1 villi are still smaller than villi of Set I; this distinction disappears by about the fourth day after hatching. The significance of the morphological changes in epithelial cells is discussed in terms of several hypotheses bearing on the mechanisms of villus formation.

Regulation of adult intestinal epithelial stem cell development by thyroid hormone during Xenopus laevis metamorphosis

“…Several rows of straight folds running longitudinally are first formed, then increase in number and height, and are finally modified into a zigzag pattern Dixon, 1977, 1978;Ishizuya-Oka and Shimozawa, 1987a). These morphogenetic processes are essentially the same as those reported in the avian small intestine (Grey, 1972), although the avian zigzag folds are further differentiated into definitive villi. With the progress of fold formation, the amphibian adult epithelium also acquires the cell-renewal system similar to that in higher vertebrates.…”

Anisotropic growth shapes intestinal tissues during embryogenesis

“…The different steps described for chick (14,15) and turkey embryos (18) show that not a unique mechanism will explain Fig. 1.…”

“…Here, we aim to describe the early stages of villi formation during chick duodenum growth (14)(15)(16). Initially, the small cylinder interior covered by a bilayer made by the mesenchyme and the mucosal epithelium is smooth, and then folds appear, bulging into the lumen approximately during the midperiod between incubation and hatching (Figs.…”

“…The appearance of the zigzag instability in intestine growth is common to many embryos such as humans (19,20), avians (14)(15)(16)18), pisces (21,22), and different parts of the small intestine (duodenum and jejenum). The large intestine does not present villi, which is explained by its different functions in physiology.…”

“…From his figures 6-8 in ref. 15, an estimation of 100 μm can be given for the distance between two rows of previlli, which reach an amplitude of 10 μm when the zigzag occurs. A few years later, Burgess (16), also with electron microscopy, reexamined the previlli formation in chick duodenum, exhibiting more clearly the relative size of the mesenchyme versus the mucosal epithelium, and favored the role of the epithelium growth, although he did not discard completely the mesenchyme-epithelium interaction.…”