Stereological methods for estimating the functional surfaces of the chiropteran small intestine

A tissue sampling protocol has been devised for studying the functional surfaces of chiropteran small intestine and drawing comparisons within and between species. The goal was to obtain minimally biased stereological estimates of villous and microvillous surface areas and the numbers of microvilli. The approach is illustrated using the intestines of 3 bats (from frugivorous and entomophagous groups) and is based on the use of vertical sections and cycloid test arcs. A sampling scheme with 3 levels was employed. At level 1 (macroscopy), primary mucosal area was estimated from intestinal length and perimeter. Amplification factors due to villi were estimated at level 2 (light microscopy, LM) whilst microvillous amplifications were estimated at level 3 (transmission electron microscopy, TEM). The absolute surfaces, lengths and diameters of microvilli were used to calculate packing densities and absolute numbers. Estimated villous surface areas of the entire small intestine were 44.4 cm² (Miniopterus inflatus, entomophagous), 410 cm² (Epomophorus wahlbergi, frugivorous) and 237 cm² (Lisonycteris angolensis, frugivorous). Corresponding microvillous surface areas were 0.11, 1.69 and 1.01 m² whilst the numbers of microvilli per intestine were 4.5, 23.4 and 8.8 x 10¹¹. When normalised for body weights, microvillous surfaces were 122, 246 and 133 cm²/g respectively. The functional surfaces of the fruit bat appear to be more extensive than those of the entomophagous bat.