Editing Endocrine system (section)

===Gonads===
{{Main|Development of the gonads}}

The reproductive system begins development at four to five weeks of gestation with germ cell migration. The bipotential gonad results from the collection of the medioventral region of the [[urogenital ridge]]. At the five-week point, the developing [[Gonad|gonads]] break away from the adrenal primordium. Gonadal differentiation begins 42 days following conception.

====Male gonadal development====
For males, the [[Testicles|testes]] form at six fetal weeks and the sertoli cells begin developing by the eight week of gestation. [[SRY]], the sex-determining locus, serves to differentiate the [[Sertoli cell]]s. The Sertoli cells are the point of origin for [[anti-Müllerian hormone]]. Once synthesized, the anti-Müllerian hormone initiates the ipsilateral regression of the Müllerian tract and inhibits the development of female internal features. At 10 weeks of gestation, the Leydig cells begin to produce androgen hormones. The androgen hormone dihydrotestosterone is responsible for the development of the male external genitalia.

The testicles descend during prenatal development in a two-stage process that begins at eight weeks of gestation and continues through the middle of the third trimester. During the transabdominal stage (8 to 15 weeks of gestation), the [[Gubernaculum|gubernacular ligament]] contracts and begins to thicken. The craniosuspensory ligament begins to break down. This stage is regulated by the secretion of [[INSL3|insulin-like 3]] (INSL3), a relaxin-like factor produced by the testicles, and the INSL3 G-coupled receptor, LGR8. During the transinguinal phase (25 to 35 weeks of gestation), the testicles descend into the scrotum. This stage is regulated by androgens, the genitofemoral nerve, and calcitonin gene-related peptide. During the second and third trimester, testicular development concludes with the diminution of the fetal Leydig cells and the lengthening and coiling of the [[Seminiferous tubule|seminiferous cords]].

====Female gonadal development====
For females, the [[Ovary|ovaries]] become morphologically visible by the 8th week of gestation. The absence of testosterone results in the diminution of the Wolffian structures. The Müllerian structures remain and develop into the fallopian tubes, uterus, and the upper region of the vagina. The [[urogenital sinus]] develops into the urethra and lower region of the vagina, the genital tubercle develops into the clitoris, the urogenital folds develop into the labia minora, and the urogenital swellings develop into the labia majora. At 16 weeks of gestation, the ovaries produce [[Follicle-stimulating hormone receptor|FSH]] and [[Luteinizing hormone/choriogonadotropin receptor|LH/hCG receptors]]. At 20 weeks of gestation, the theca cell precursors are present and oogonia [[mitosis]] is occurring. At 25 weeks of gestation, the ovary is morphologically defined and [[folliculogenesis]] can begin.

Studies of [[gene expression]] show that a specific complement of genes, such as follistatin and multiple cyclin kinase inhibitors are involved in ovarian development. An assortment of genes and proteins - such as WNT4, RSPO1, FOXL2, and various estrogen receptors - have been shown to prevent the development of testicles or the lineage of male-type cells.