Sự hình thành và phát triển của tuyến sinh dục (gonad)

[lethehien]

Development of the Gonads
On each side of the embryo, a primitive gonad arises from the genital ridge, a condensation of tissue near the adrenal gland. The gonad develops a cortex and a medulla

Until the sixth week of development, these structures are identical in both sexes.

In genetic males, the medulla develops during the seventh and eighth weeks into a testis, and the cortex regresses. Leydig and Sertoli cells appear, and testosterone and MIS are secreted.

In genetic females, the cortex develops into an ovary and the medulla regresses. The embryonic ovary does not secrete hormones. Hormonal treatment of the mother has no effect on gonadal (as opposed to ductal and genital) differentiation in humans, although it does in some experimental animals.
Embryology of the Genitalia

In the seventh week of gestation, the embryo has both male and female primordial genital duct. In a normal female fetus, the müllerian duct system then develops into uterine tubes (oviducts) and a uterus.

In the normal male fetus, the wolffian duct system on each side develops into the epididymis and vas deferens. The external genitalia are similarly bipotential until the eighth week .

Thereafter, the urogenital slit disappears and male genitalia form, or, alternatively, it remains open and female genitalia form.





When the embryo has functional testes, male internal and external genitalia develop. The Leydig cells of the fetal testis secrete testosterone, and the Sertoli cells secrete müllerian inhibiting substance (MIS; also called müllerian regression factor, or MRF).

In their effects on the internal as opposed to the external genitalia, MIS and testosterone act unilaterally. MIS causes regression of the müllerian ducts by apoptosis on the side on which it is secreted, and testosterone fosters the development of the vas deferens and related structures from the wolffian ducts. The testosterone metabolite dihydrotestosterone induces the formation of male external genitalia and male secondary sex characteristics.

[tknguyen]

Development of the Gonads
On each side of the embryo, a primitive gonad arises from the genital ridge, a condensation of tissue near the adrenal gland. The gonad develops a cortex and a medulla

Until the sixth week of development, these structures are identical in both sexes.

In genetic males, the medulla develops during the seventh and eighth weeks into a testis, and the cortex regresses. Leydig and Sertoli cells appear, and testosterone and MIS are secreted.

In genetic females, the cortex develops into an ovary and the medulla regresses. The embryonic ovary does not secrete hormones. Hormonal treatment of the mother has no effect on gonadal (as opposed to ductal and genital) differentiation in humans, although it does in some experimental animals.
Embryology of the Genitalia

In the seventh week of gestation, the embryo has both male and female primordial genital duct. In a normal female fetus, the müllerian duct system then develops into uterine tubes (oviducts) and a uterus.

In the normal male fetus, the wolffian duct system on each side develops into the epididymis and vas deferens. The external genitalia are similarly bipotential until the eighth week .

Thereafter, the urogenital slit disappears and male genitalia form, or, alternatively, it remains open and female genitalia form.





When the embryo has functional testes, male internal and external genitalia develop. The Leydig cells of the fetal testis secrete testosterone, and the Sertoli cells secrete müllerian inhibiting substance (MIS; also called müllerian regression factor, or MRF).

In their effects on the internal as opposed to the external genitalia, MIS and testosterone act unilaterally. MIS causes regression of the müllerian ducts by apoptosis on the side on which it is secreted, and testosterone fosters the development of the vas deferens and related structures from the wolffian ducts. The testosterone metabolite dihydrotestosterone induces the formation of male external genitalia and male secondary sex characteristics.

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1. http://www.ycantho.com/qa/showthread.php?1190-Gonad
2. Download Reproductive System