Medical brain notes 44

  Physiologic Anatomy of the Female Sexual Organs Figures 81–1 and 81–2 show the principal organs of the human female reproductive tract, the most important of which are the  ovaries, fallopian tubes, uterus,  and  vagina.  Reproduction begins with the development of ova in the ovaries. In the middle of each monthly sexual cycle, a single ovum is expelled from an ovarian follicle into the abdominal cavity near the open fimbriated ends of the two fallopian tubes. This ovum then passes through one of the fallopian tubes into the uterus; if it has been fertilized by a sperm, it implants in the uterus, where it develops into a fetus, a placenta, and fetal membranes—and eventually into a baby.         During fetal life, the outer surface of the ovary is covered by a  germinal epithe-lium,  which embryologically is derived from the epithelium of the germinal ridges.As the female fetus develops,  primordial ova  di...

  Female Hormonal System The female hormonal system, like that of the male, consists of three hierarchies of hormones, as follows: 1.                A hypothalamic releasing hormone,  gonadotropin-releasing hormone(GnRH) 2.                The anterior pituitary sex hormones,  follicle-stimulating hormone (FSH)  and  luteinizing hormone (LH),  both of which are secreted in response to the release of GnRH from the hypothalamus 3.                The ovarian hormones,  estrogen  and  progesterone,  which are secreted by the ovaries in response to the two female sex hormones from the anterior pituitary gland         These various hormones are not secreted in constant amounts throughout the female month...

  Monthly Ovarian Cycle; Function of the Gonadotropic Hormones The normal reproductive years of the female are characterized by monthly rhythmical changes in the rates of secretion of the female hormones and correspon-ding physical changes in the ovaries and other sexual organs. This rhythmical pattern is called the  femalemonthly sexual cycle  (or, less accurately, the  menstrual cycle ). The duration of the cycle averages 28 days. Itmay be as short as 20 days or as long as 45 days in some women, although abnormal cycle length is frequently associated with decreased fertility. There are two significant results of the female sexual cycle. First, only a  single  ovum is normally released from the ovaries each month, so that normally only a single fetus will begin to grow at a time. Second, the uterine endometrium is prepared in advance for implantation of the fertilized ovum at the required time of the month. Gonadotropic Hormones and Their Effects on the Ov...

  Gonadotropic Hormones and Their Effects on the Ovaries The ovarian changes that occur during the sexual cycle depend completely on the gonadotropic hormones  FSH  and  LH,  secreted by the anterior pituitary gland. In the absence of these hormones, the ovaries remain inactive, which is the case throughout childhood, when almost no pituitary gonadotropic hormones are secreted. At age 9 to 12 years, the pituitary begins to secrete progressively more FSH and LH, which leads to onset of normal monthly sexual cycles beginning between the ages of 11 and 15 years. This period of change is called  puberty,  and the time of the first men-strual cycle is called  menarche.  Both FSH and LH are small glycoproteins having molecular weights of about 30,000. During each month of the female sexual cycle, there is a cyclical increase and decrease of both FSH and LH, as shown in the bottom of Figure 81–3. These cyclical variations cause cyclical ovarian chan...

  Ovarian Follicle Growth- “Follicular” Phase of the Ovarian Cycle Figure 81–4 shows the progressive stages of follicular growth in the ovaries. When a female child is born, each ovum is surrounded by a single layer of granu-losa cells; the ovum, with this granulosa cell sheath, is called a  primordial follicle,  as shown in the figure. Throughout childhood, the granulosa cells are believed to provide nourishment for the ovum and to secrete an  oocyte maturation-inhibiting factor  that keeps the ovum suspended in its primordial state in the prophase stage of meiotic division. Then, after puberty, when FSH and LH from the anterior pituitary gland begin to be secreted in significant quantities, the  ovaries, together with some of the follicles within them, begin to grow. The first stage of follicular growth is moderate enlargement of the ovum itself, which increases in diameter twofold to threefold. Then follows growth of additional layers of granulosa cells ...

  Corpus Luteum-“Luteal” Phase of the Ovarian Cycle During the first few hours after expulsion of the ovum from the follicle, the remaining granulosa and theca interna cells change rapidly into  lutein cells.  They enlarge in diameter two or more times and become filled with lipid inclusions that give them a yellowish appearance.This process is called  luteinization,  and the  total mass of cells together is called the   corpus luteum,   which is shown in Figure 81–4. A well-developed vascular supply also grows into the corpus luteum. The granulosa cells in the corpus luteum develop extensive intracellular smooth endoplasmic reticula that form large amounts of the female sex hormones  progesterone  and  estrogen  (more progesterone thanestrogen). The theca cells form mainly the androgens androstenedione  and  testosterone  rather than femalesex hormones. However, most of these hormones are also converted by the g...

  Functions of the Ovarian Hormones-Estradiol and Progesterone The two types of ovarian sex hormones are the  estro-gens  and the  progestins.  By far the most important ofthe estrogens is the hormone  estradiol,  and by far the most important progestin is  progesterone.  The estro-gens mainly promote proliferation and growth of spe-cific cells in the body that are responsible for the development of most secondary sexual characteristics of the female. The progestins function mainly to prepare the uterus for pregnancy and the breasts for lactation. Chemistry of the Sex Hormones Estrogens.  In the normal nonpregnant female, estro-gens are secreted in significant quantities only by the ovaries, although minute amounts are also secreted by the adrenal cortices. During  pregnancy,  tremendous quantities of estrogens are also secreted by the placenta. Only three estrogens are present in significant quan-tities in the plasma of the hu...