By the tenth week, the loss of wolf an ducts allows the müllerian ducts to join and become the uterus, fallopian tubes, cervix, and upper two thirds of the vagina. The fallopian tubes carry ova from the ovaries to the uterus during a woman’s reproductive years. Like the internal reproductive structures, the external structures develop from homologous embryonic tissues. During the first 7 to 8 weeks of gestation, both male and female embryos develop an elevated structure called the genital tubercle (Figure 23-2). Testosterone is necessary for the genital tubercle to differentiate into male genitalia; otherwise, female genitalia develop, which may occur even in the absence of ovaries possibly because of the presence of placental estrogens. Anterior pituitary gland development starts between the 4th and 6th weeks of fetal life, and the vascular connection between the hypothalamus and the pituitary is established by the 12th week. Gonadotropin-releasing hormone (GnRH) is produced in the hypothalamus by 10 weeks’ gestation and controls the production of two gonadotropins by the anterior pituitary gland, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In the female fetus, high levels of FSH and LH are excreted. FSH and LH stimulate the production of estrogen and progesterone by the ovary. The production of FSH and LH rises until about 28 weeks’ gestation, until the production of estrogen and progesterone by the ovaries and placenta is high enough to result in the decline of gonadotropin production. Production of primitive female gametes (ova) occurs solely during fetal life. From puberty to menopause, one female gamete matures per menstrual cycle. Production of the male gametes (sperm) begins at puberty; after that millions are produced daily, usually for life (p. 769). CONCEPT 5; QUESTION 34; PAGE 112 Two factors help maintain the self-cleansing action of the vagina and defend it from infection, particularly during the reproductive years: (1) an acid-base balance that discourages the proliferation of most pathogenic bacteria and (2) the thickness of the vaginal epithelium. Before puberty, vaginal pH is about 7 (neutral) and the vaginal epithelium is thin. At puberty the pH becomes more acidic (4 to 5) and the squamous epithelial lining thickens. These changes are
maintained until menopause (cessation of menstruation), at which time the pH rises again to more alkaline levels and the epithelium thins out. Therefore, protection from infection is greatest during the years when a woman is most likely to be sexually active. Between puberty and menopause, vulnerability to infection varies somewhat with cyclic changes in pH and epithelial thick- ness. Both defenses are greatest when estrogen levels are high and the vagina contains a normal population of Lactobacillus acidophilus, a harmless resident bacterium that helps maintain pH at acidic levels. Any condition that causes vaginal pH to rise, such as douching or use of vaginal sprays or deodorants, low estrogen levels, or destruction of L. acidophilus by antibiotics, lowers vaginal defenses against infection (p 773).
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- Spring '17
- delayed puberty, Precocious puberty, central precocious puberty