Paramesonephros

TT Paramesonephric duct
Urogenital sinus of female human embryo of eight and a half to nine weeks old.
Tail end of human embryo, from eight and a half to nine weeks old.
Details
Carnegie stage	17
Precursor	Intermediate mesoderm
Identifiers
Latin	ductus paramesonephricus
MeSH	A16.254.570
Code	TE E5.7.2.3.0.0.3
Anatomical terminology []

Paramesonephric ducts (or Müllerian ducts) are paired ducts of the embryo that run down the lateral sides of the urogenital ridge and terminate at the sinus tubercle in the primitive urogenital sinus. In the female, they will develop to form the uterine tubes, uterus, cervix, and the upper one-third of the vagina; in the male, they are lost. These ducts are made of tissue of mesodermal origin.

The female reproductive system is composed of two embryological segments: the urogenital sinus and the paramesonephric ducts. The two are conjoined at the sinus tubercle. Paramesonephric ducts are present on the embryo of both sexes. Only in females do they develop into reproductive organs. They degenerate in males of certain species, but the adjoining mesonephric ducts develop into male reproductive organs. The sex based differences in the contributions of the paramesonephric ducts to reproductive organs is based on the presence, and degree of presence, of Müllerian inhibiting factor.

During the formation of the reproductive system, the paramesonephric ducts are formed just lateral to the mesonephric ducts in both female and male embryos 6 weeks after fertilization. During this time primordial germ cells migrate from the yolk sac to the gonadal ridge; a region of mesenchyme arising from, and running parallel with, the mesonephros. The paramesonephric ducts are formed by the craniocaudal invagination of a ribbon of thickened coelomic epithelium that extends from the third thoracic segment caudally to the posterior wall of the urogenital sinus. The caudal parts of the paramesonephric ducts fuse into a single tube, known as the uterovaginal primordium, before flowing into the dorsal aspect of the urogenital sinus at the sinus tubercle directly medial to the mesonephric ducts.