THE RAT URETER. FINE STRUCTURAL CHANGES DURING ITS DEVELOPMENT

Abstract

Pre- and post-natal development of the rat ureter was studied. The epithelium at first is simple cuboidal and becomes stratified transitional in type at birth. The complexity of the basement membrane, the stellate ("collapsed") outline to the lumen, the presence of elastin in the lamina propria and of a fully developed muscularis are associated with function and are present only by the 5th post-natal day. The acquisition of the above features occurs rapidly in the last 2-3 days of gestation and in the 1st 5 days of post-natal life. It is concluded that while the metanephros may be capable of urinary function before birth, it does not secrete copious quantities of urine until the placenta, as the principal excretory organ, is lost.