Surface Enlargement in the Large-Intestine of the Koala (Phascolarctos-Cinereus) - Morphometric Parameters

Abstract

Morphometric data are presented for various parameters of the large intestine of the koala (Phascolarctos cinereus). For the first time, empirical values are provided that substantiate the morphologically obvious enormous development of the caecum and proximal colon in this herbivorous marsupial. By use of a computer-aided planimeter the basal or ground surface areas of the caecum and colon were determined. On paraffin-embedded material the surface enlargement of the mucosa due to microscopically visible folds or plicae was measured. This is expressed in the form of a surface-enlargement factor which was multiplied by the basal surface areas to give total surface areas. The basal surface areas (with percentage of entire intestine in parentheses) are: caecum, 890.6 cm2 (32.0%); colon, 1434.8 cm2 (51.5%); and entire (large and small) intestine, 2785.0 cm2. In the caecum and proximal colon of the koala, 8-14 longitudinal folds augment the surface area enormously. Basal areas plus that additional area afforded by the folds amount to: caecum, 3659.8 (45.9%); colon, 3854.0 (48.3%); and entire intestine, 7973.4 cm2. Respective total areas (surface enlargement factor x basal area) are: caecum, 10 979.5 cm2 (44.9%); colon, 9808.5 cm2 (40.1%); and entire intestine, 24 464.7 cm2 (= 2.4 m2).