Anatomical And Morphological Relationships Of The Female Reproductive System

A. Introduction

The human female reproductive system comprises the gonads (two ovaries) and uterine tubes, a single uterus, a vagina, external genitalia, and the mammary glands. These are diagrammed in Figure 13-1 with the exception of the mammary glands, which are diagrammed in Figure 14-5.

The key steps of organogenesis of the sexually indifferent, yet chromosomally determined female gonad are discussed in Chapter 14. The presentation in this chapter will begin with the generation of a morphologically identifiable ovary.

B. Ovaries

The adult human ovary is 4-5 cm in length and is almond-shaped. Structurally each ovary consists of the cortex (outer) and medulla (inner) zones (see Figure 13-2). Just below the surface layer of connective tissue is the germinal epithelium, which is the site of generation of the follicles. Each primary follicle contains one central germ cell or oogonium, which is surrounded by a layer of epithelial cells. Surrounding the follicular cells, but separated by a basement membrane, are the theca externa and theca interna cells (see insert box of Figure 13-3). The medulla comprises the central region of the ovary, which is devoid of follicles. The normally functioning ovary undergoes, over a 4-5 decade interval, a series of profound changes that are essential for female development, puberty, reproduction, and menopause.

The ovarian follicle consists of a large round oocyte surrounded by follicular cells. After ovulation, the walls of the follicle collapse and cells from the thecal layer invade the granulosa layer to form the corpus luteum. If pregnancy does not occur, the corpus luteum lasts for only 14 days when it becomes replaced with fibrous tissue to form the corpus albicans. Prior to ovulation, the theca interna cells and follicular cells collaborate to biosynthesize estrogens.

The process of gametogenesis in the female is termed oogenesis. In contrast to the comparable process in the male (spermatogenesis), which is initiated in puberty and continues throughout the bulk of adult life, the process of germ cell production in the female occurs exclusively in embryonic life (see also Table 125 for other female-male comparisons).

During embryogenesis, the oogonia or primordial germ cells available for a lifetime of ovulation are produced. The process of oogenesis is initiated in weeks 8-20 of intrauterine life and continues in defined stages through puberty until the final stage of generation of a mature ovum occurs in a menstrual cycle (see Figure 13-3). By the 20th week of gestation there are ~7 million mitotic germ cells in each ovary. These germ cells then cease to divide by mitosis; some become atretic while others mature to the oogonium stage and proceed by meiotic division to the leptotene or arrested prophase stage. These individual oogonia become surrounded by mesenchymal cells to form the primary follicles (see Figure 13-2). By birth the number of follicles in an ovary number only 1-2 million; this number then decreases

Sacrum

Broad ligament of uterus

Coccyx

Fornix

Cervix

Ligaments Female Reproductive System

5uspensory ligament Fallopian i üb« Ovary Uterus

Round ligament of uterus

Urinary bladder Urethra Symphysis pubis

Rectum

Anus

Vagina

Clitoris

Labium minus Labium majus figure 13-1 Female reproductive organs (midsagittal view).

5uspensory ligament Fallopian i üb« Ovary Uterus

Round ligament of uterus

Sacrum

Broad ligament of uterus

Coccyx

Fornix

Rectum

Anus

Vagina

Urinary bladder Urethra Symphysis pubis

Clitoris

Labium minus Labium majus

Cervix figure 13-1 Female reproductive organs (midsagittal view).

by further atresia and cell death, so that by puberty there are only « 400,000 oogonia in follicles to support the monthly ovulatory cycles over the next 35-40 years. These oogonia continue in the leptotene (ar rested prophase) state until a limited number are selected by an as yet poorly understood endocrine process for further maturation, which leads to ovulation and the release of one mature ovum per month.

Germinal follicle epithelium

Corpus Hemorrhagicum

Corpus hemorrhagicum

Blood vessels

Corpus albicans

Mature follicle Antrum

Atretic follicle

Interstitial Young cell mass corpus luteum figure 13-2 Schematic diagram of a mammalian ovary. The sequence of events necessary for the origin, growth, and rupture of a typical ovarian-Graafian follicle and the concomitant formation and subsequent regression of the corpus luteum is presented. The sequence should be followed clockwise around the ovary beginning with the germinal epithelium at 10 o'clock. The inset box illustrates a section of the wall of a mature follicle. Both the thecal and granulosa cells acquire the capability for the biosynthesis of estradiol, while the corpus luteum is the principal site of production of progesterone (see also Figure 13-12). Modified with permission from Katzund, B. G. (ed) (1984). "Basic and Clinical Endocrinology," 2nd ed. Lange Medical Publications, Los Altos, CA.

Primary Secondary Primordial follicle follicle Vesicular

Germinal follicle epithelium

Theca externa

Theca interna Granulosa

Follicular fluid

Regressing corpus luteum

Mature corpus luteum

Corpus hemorrhagicum

Ovulated oocyte

+1 0

Post a comment