Development of the urinary system: Serial section study of 4 and 6 mm rat and 10 mm pig embryos.

ABSTRACT

The urogenital system develops from the intermediate mesoderm, the coelomic epithelium and the endoderm of the urogenital sinus. The urinary system of mammals is characterized by three sets of kidney the nonfunctional pronephroi, the mesonephroi and the functional metanephroi. The metanephroi or the permanent kidneys develop from the metanephric diverticulum and metanephrogenic tissue. At first the kidneys are located in the pelvis but later gradually ascend to the abdomen. The urinary bladder develops from the urogenital sinus and surrounding splanchnic mesoderm. In studying the development of the human urinary system at the Department of Anatomy, Siriraj Hospital, we have employed serial sections of 10-15 mm pig embryos as laboratory models. This method of study is helpful in understanding and recognizing how the kidney forms. However, pig embryos are not commercially available anymore, it is necessary to study the normal development of the kidney in other mammals. This study demonstrates that 6 mm rat embryos can be used instead of pig embryos as the development of the metanephros is very similar, although, in the rat embryo, the mesonephros is much smaller than that of a pig embryo and the subcardinal vein cannot be identified. However, it should be borne in mind that the human mesonephros is also smaller than that of pigs. For this reason, the rat embryo is still suitable for use as a laboratory model.