Paramesonephric duct

Paramesonephric duct
Paramesonephric ducts (labelled as Müllerian ducts) shown in a human fetus of eight and a half to nine weeks old.
Details
Carnegie stage	17
Precursor	Intermediate mesoderm
Identifiers
Latin	ductus paramesonephricus
MeSH	D009095
TE	duct_by_E5.7.2.3.0.0.3 E5.7.2.3.0.0.3
Anatomical terminology [edit on Wikidata]

The paramesonephric ducts (or Müllerian ducts) are paired ducts in the embryonic development of the reproductive system of humans and other placental mammals. The ducts run down the lateral sides of the genital ridge, and terminate at the sinus tubercle in the primitive urogenital sinus.^[1] In humans they form in the embryo during the 6th week of gestational age, before sexual differentiation takes place. In the differentiated female, the paramesonephric ducts develop into the reproductive tract, that includes the fallopian tubes (oviducts), uterus, cervix, and the upper part of the vagina.^[2]

In the male-determined embryo, the testes produce two hormones responsible for masculinization – anti-Müllerian hormone (AMH), and testosterone. Sertoli cells secrete AMH, during weeks six and seven, which causes the paramesonephric ducts to regress. In week eight Leydig cells secrete testosterone which stimulates the formation of male genitals from the mesonephric ducts.^[3]

Each paramesonephric duct is situated just lateral to each mesonephric duct (Wolffian duct). The mesonephric ducts are not completely useless in the female case: they secrete protein Wnt-9b, which is necessary for the elongation of the paramesonephric ducts. Elongation also happens through the active migration of the paramesonephric epithelium, which happens through a phosphoinositide 3-kinase pathway.^[4]