Liver development in rats during the embryonic period (Carnegie stages 11-14)

The hepatic structures appearing during Carnegie stages 11-14 were analyzed in a series of 61 OFA rat embryos. The group of embryos (crown-rump length 2-7 mm, 10th-12th days after coitus) was composed of 52 specimens of the somite period (stages 11 and 12) and of 9 specimens of the postsomite period (stages 13 and 14). The embryos were submitted to serial histological sectioning with graphic reconstruction. Stage 11 was characterized by the development of the hepatic diverticulum induced by differential growth of the endodermal plate and fixed contact between the entoderm and endothelium lining the heart. Stage 12 presented obvious signs of cellular differentiation, the septum transversum giving the liver stroma and the hepatic diverticulum the epithelial trabecula. At stage 13 the epithelial cords enmeshed the stromal capillaries, while hepatocardiac veins drained the hepatic flow into the sinus venosus. Stage 14 was recognized by the presence and development of the hepatic lobes and the enlargement of vascular channels. The cystic bud was never observed. The identification of these features permits to precise the hepatic developmental staging in rats and to obtain accurate criteria for the characterization of the end of the somite period and the beginning of the postsomite period.