A simple polynomial model of the growth of the gastro-intestinal tract in the mouse embryo.

The growth in volume of the epithelium and mesenchyme of the intestine and stomach was estimated in mouse embryos aged between 11.6 days after fertilization and birth, by means of a morphometric technique. The findings on the growth in volume of the stomach confirm the results obtained for the intestine: the epithelium grows faster than the mesenchyme and the retardation rate of the former exceeds that of the latter. In roughly the same period, the relative increase in volume is much greater for the epithelium of the intestine than for that of the stomach. However, the relative increase in volume of the mesenchyme of the intestine is similar to that of the gastric mesenchyme. A set of data can often be described by several regression equations, the choice of the function depending on the investigator's purpose and knowledge of the process under study. The growth data were first fitted by exponential and then by polynomial functions. Both fits permit an accurate linear representation of the results, but only the polynomial description permits the expression of properties like summation and the introduction of the beginning of the growth process into the growth equation as an additional parameter. Furthermore, while the specific growth rates given by the exponential model slow down with a constant rate of decrease, those given by the polynomial model seem to reach an exponential retardation. This is in accordance with other growth concepts formulated in the past.