泌尿生殖系统的发生.pdf

第23 章 泌尿系统和生殖系统的发生 CHAPTER 23 DEVELOPMENT OF UROGENITAL SYSTEM KEY POINTS ·Development of pronephros ·Development of mesonephros ·Development of metanephros ·Malformation of the urinary system ·Development and sexual differentiation of gonads ·Development and sexual differentiation of genital ducts ·Development and sexual differentiation of external genitalia ·Malformation of the genital system OUTLINE Functionally the urogenital system can be divided into two entirely different components: the urinary system and the genital system. Embryologically and anatomically, however, they are intimately interwoven. Both develop from intermediate mesoderm along the posterior wall of the abdomenal cavity, and initially the excretory ducts of both systems enter a common cavity, the cloaca. Three slightly overlapping kidney systems are formed in a cranial to caudal sequence during intrauterine life in humans:the pronephros, mesonephros, and metanephros. The pronephros is represented by a few cell clusters and tortuous tubular structrures in the neck.The pronephric ducts run caudally and open into the cloaca. The rudimentary pronephroi soon degenerate; however, most of the pronephric ducts persist and utilized by the next set of kidneys. The mesonephros which forms in the thoracic and lumbar regions,is large and characrerized by excretory units(nephrons) and its owen collecting duct, the mesonephric or wolffian duct. In human it may only function briefly, most of the system disappears. In male, the ducts and a part of 308 tubules of the mesonephros form the conduct for sperm from the testes to the urethra. In