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The proliferation sites and cellular kinetics of villous epithelial cells and M cells in the intestine of the adult chicken have never been clarified. In this study, we determined the proliferation sites in the chicken caecum using colchicine treatment and detection of proliferative cell nuclear antigen (PCNA). The cellular kinetics of these cells were also studied using bromodeoxyuridine (BrdU) as a tracer. Enterocytes in their mitotic period were observed along the entire length of the intestinal crypt of the caecum, with a denser distribution in the middle portion of the crypt, except for the caecal tonsil. The centres of distributions were at 49% of the distance from the bottom of the crypt in the base and 41% in the apex of the caecum. In the caecal tonsil, the centres of distributions were at 64% in the long type of crypt from the bottom of the crypt and at 44% in the short type of crypt. On the other hand, the PCNA-positive enterocytes were distributed more densely at the bottom of the crypt, except for the caecal tonsil. The centres of distributions were at 36% in the base from the bottom of the crypt, 37% in the body, and 34% in the apex. In the caecal tonsil, they were at 54% in the long type of crypt and 44% in the short type. The BrdU-labelled enterocytes reached to the basement of the intestinal villi in all caecal portions at 1 d after the BrdU administration. The leading edge of the labelled enterocytes disappeared from the villous tips at 4 d in the base and the body and 3 d in the apex. In the caecal tonsil, the BrdU-labelled microvillous epithelial cells and the M cells appeared near the orifice of the crypt at 1 d, and BrdU-labelled M cells were not observed in the crypt. Thereafter, almost all of these cells disappeared at 5 d from the follicle associated epithelium (FAE). These results suggest that M cells are transformed from their precursors within 1 d, and the turnover time for M cells occurs within 4 d after the cell division of the precursors.

A peculiar structure, observed as a dome-like protrusion at the apex of the caecum, was investigated macroscopically and histologically in healthy White Leghorn chickens. It was hemispheric or spherical in shape and as it consisted of a lumen with a wall occupied by lymphoid tissue, this structure was designated the apical caecal diverticulum (ACD). ACD were detected in 25.2% of examined chickens and had a mean diameter and height of 1.9 mm and 1.2 mm respectively. Histologically, both the lamina propria mucosae and the submucosa of ACD consisted of well developed aggregated lymphoid nodules. Each nodule was covered by follicle-associated epithelium which contained cells resembling M cells. Some secondary nodules extended into the subserosa. The muscularis mucosae and the stratum circulae of the tunica muscularis disappeared near the entrance to ACD. The stratum longitudinale also gradually decreased in thickness around the entrance, becoming an extremely thin layer in the diverticulum wall. At the caecal apex, each stratum of the tunica muscularis was thinner than in the caecal body and separated into several muscle bundles. These bundles were occasionally displaced by developed lymphoid nodules, causing them to protrude into the subserosa. The high frequency of ACD suggests that caecal apex may be sites for immunological surveillance in the chicken caecum. In addition to the intense and frequent antiperistalsis at the apex suggested by Yasukawa (1959), possible causes for the formation of ACD included (1) the fragility of the tunica muscularis at the ACD, and (2) the local removal of the physical supporting structures by the development of lymphoid nodules.

This study was undertaken in order to compare cell proliferation at different sites along the length of the large bowel of the mouse. Simple morphometry has been used along with 3HTdR labelling studies and metaphase arrest with vincristine. Differences have been described in the shape and size of crypts, the distribution of proliferating cells, the duration of the cell cycle, as well as in the rate of cell production by the crypts. The findings explain some of the apparent inconsistencies in the literature.

The caecal mucosa of the rabbit has been studied using transmission electron microscopy and its fine structure is considered in the light of its known secretory and absorptive capacities. The luminal surface consists of columnar absorptive epithelium while the crypts are lined with glandular epithelium comprising undifferentiated cells, goblet cells containing dark and light mucigenous granules, and intra-epithelial cells. Endocrine cells occur more commonly in the cryptal epithelium and two cell types have been recognised which correspond to EC and L cells respectively. The lamina propria includes lymphocytes, plasma cells, mast cell and smooth muscle cells. There is little ultrastructural variation within mucosal cells along the length of the caecum.