The objective of this study was to investigate the size of the small and large intestine in postnatal development of Mus musculus mice. The gut was obtained from 2-, 4-, 6-, and 12-week-old animals. The morphometric analysis was performed at microscopic level. Measurements and calculations included dimensions of villi (height, diameter) and their number per 1 mm² surface area in the proximal, middle, and distal section of the small intestine, as well as the length and surface area (external and internal) of the small and large intestines.
To find the allometric relationship between the size of the small and large intestines and body mass, reduced major axis regression was applied. The length and surface area of both intestinal segments gradually increased with age. The increase in the internal surface area of the small intestine was the result of lengthening of the intestine and increasing diameter of the villi in its proximal and middle sections. No increase in villus height during the studied period was detected. A marked increase in the size of the intestinal segments was observed between the 2^nd and 4^th weeks of life, when the length doubled and the surface area tripled in size. Allometric analysis revealed that the increase in length and internal surface area of the small and large intestines was more rapid than the body mass increase during the weaning period, while it was not different from isometry after the weaning. In conclusion, the greatest changes in the structure and size of the small and large intestines of mice occurred in the weaning period. During this period these two segments of intestine grew faster than the rest of the body and reached adult proportions. (Folia Morphol 2011; 70, 4: 252–259)