Introduction

Prenatal Development

The first factor determining sexual differentiation during embryologie development is chromosomal sex. This is determined by which sex chromosome is present in the fertilizing sperm. The reproductive system develops from a common undifferentiated primordium. The primitive gonad has the potential to form either testis from its medullary portion or ovary from its cortical portion. The influence of a gene(s) on the Y chromosome (SRY), interacting with a gene(s) on the autosomes (SOX9, SF1, WT1, and others), determines that the medullary portion of the undifferentiated primordial gonad will develop into seminiferous tubules, which become recognizable between seven and eigth weeks of gestation. Absence of the testicular differentiating genes or a disturbance in the timing of various interactions will result in differentiation of the primordial gonad into an ovary. Recognition of ovarian tissue occurs by the 10th week of gestation. Even though early ovarian differentiation can take place when only one X chromosome is present, a second X chromosome is necessary for the complete development and maintenance of ovarian tissue. In Turner syndrome, where all or part of one X chromosome is missing, degeneration of some of the ovarian structures usually occurs before birth.

The second factor in sex differentiation is the gonadal sex. At about seven weeks of gestation, the testes in the male begin to secrete androgens which induce the development of the male internal ductal and genital structures, the epididymis, ductus deferens, and seminal vesicles from the Wolffian ducts. In the male, the structures of the Mullerian ducts degenerate under the influence of the nonsteroidal Mullerian inhibitory factor, which is secreted by the embryonic testes starting at about eight weeks of gestation. Inadequate production of androgens in a male fetus results in degeneration of the Wolffian ducts and Wolffian duct structures. Absence of Mullerian inhibitory factor results in Mullerian structures being present in the male. In the female fetus, the Mullerian duct differentiates autonomously into the fallopian tube, uterus, and proximal vagina. In the female, the Wolffian duct structures degenerate because of the lower level of androgen present.

In the male, under the influence of circulating androgens, the urogenital folds fuse to form a urethra, and the penis is formed by the growth of the genital tubercle (Fig. 10.1). The labioscrotal swellings develop into the scrotum, and the testes descend into the inguinal canal at about six months of gestation. Shortly before birth the testes enter the scrotum under the influence of gonadotropin stimulation. Failure of the testes to descend into the scrotum is called cryptorchidism and may be unilateral or bilateral. The internal ductal structures develop from the same primor-dia as the urinary tract. In the presence of androgens, the prostate gland develops from the vesicourethral canal.

In the female fetus, the clitoris (Fig. 10.1) develops from the genital tubercle; the urogenital groove remains open; the urogenital folds develop

Figure 10.1 Differentiation of external genitalia in the human fetus.

Figure 10.1 Differentiation of external genitalia in the human fetus.

Genital

Sexual development of baby at 2nd to 3rd month of pregnancy

Genital

Sexual development of baby at 2nd to 3rd month of pregnancy

Male and female identical

Genita tuberc (clitori

Male and female identical

Genita tuberc (clitori

Female

Genital tubercle (penis)

Sexual development

Vulval groove of baby at 3rd to 4th month of pregnancy

Outer labial swelling

Pregnancy And Childbirth

Pregnancy And Childbirth

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