Morphological study of the caecal epithelium of the chicken (Gallus gallus domesticus L.).

1. The structure of the chicken caecal epithelium has been investigated at macroscopic and microscopic levels (scanning and transmission electron microscopy). 2. Morphological data distinguish three regions in the caecum: proximal, with well developed villi, but smaller and less numerous than those present at mid-jejunum; medial, with longitudinal folds and small villi, and distal, with longitudinal and transverse folds and small villi similar to those of the medial region. 3. Microvilli of enterocytes from the tip of the villus of the proximal caecum are shorter and thinner than jejunal microvilli; microvilli of medial and distal regions are poorly developed. 4. There is a decrease in microvillus surface area along the villus axis as a result of the progressive decrease of microvillus length from the tip of the villus to the crypt, both in the proximal caecum and jejunum. In tip of the villus, the amplification of apical surface due to microvilli is 24, 12.7 and 14 times in proximal, medial and distal caecum, respectively, while in the jejunum the amplification factor is 33.1. 5. The higher development of proximal caecal apical surface supports the view that this region is better adapted for the absorption of nutrients that the other caecal regions.