accessory organs include both internal and external reproductive organs (fig. 1-61). OVARIES The ovaries, as stated earlier, are the primary female reproductive organs, producing the female sex cells and sex hormones (fig. 1-61). Structure The ovaries, or female gonads, are two almond-shaped glands suspended by ligaments in the upper pelvic cavity. There is one ovary on each side of the uterus. The ligaments that suspend the ovaries contain ovarian blood vessels and nerves. The tissues of an ovary are divided into two regions, an inner medulla and an outer cortex. The ovarian medulla is largely composed of loose connective tissue, numerous blood vessels, lymph vessels, and nerves. The ovarian cortex is composed of compact tissue containing tiny masses of cells called ovarian (primordial) follicles. The follicles contain the female sex cells or ova. The external surface of the ovary is covered by a layer of cuboidal epithelium cells. Beneath the epithelium is a layer of dense connective tissue. Primordial Follicle In the outer region of the ovarian cortex, microscopic groups of cells are referred to as primordial follicles. The primordial follicles consist of a single large cell, called an oocyte, which is surrounded by a layer of flattened epithelial cells called follicular cells. The oocyte is an immature egg cell. Follicular cells surround a developing egg cell and secrete female sex hormones. There are approximately 400,000 primordial follicles at puberty. Of these, probably fewer than 500 will be released from the ovary during the reproductive life of a female. At puberty, the anterior pituitary gland secretes increased amounts of FSH (follicle-stimulating hormone). In response, the ovaries enlarge and many of the primordial follicles begin to mature. During this maturation process, the oocyte enlarges and the follicle cells multiply until there are 6 to 12 layers. Fluid-filled spaces begin to appear among the follicle cells. These spaces join to form a single cavity called the antrum. Ten to fourteen days after this process begins, the primordial follicle reaches maturity. The mature primordial follicle (preovulatory or graafian follicle) and its fluid-filled cavity bulges outward on the surface of the ovary, like a blister. Ovulation Ovulation is the process by which the mature oocyte is released from the primordial follicle (fig. 1-62). Ovulation is stimulated by hormones from the anterior pituitary gland. These hormones cause the mature follicle to swell rapidly and its walls to weaken. Eventually the wall ruptures, permitting the oocyte and 1 or 2 layers of follicle cells to be released from the ovary's surface. After ovulation, the oocyte is usually propelled to the opening of a nearby fallopian tube. If the oocyte is not fertilized by a sperm cell within a relatively short time, it will degenerate. This process of ovulation occurs once a month. Each ovary normally releases an ovum every 56 days. The right and left ovary alternately discharge an ovum approximately every 28 days. The menstrual cycle in most women is therefore approximately 28 days. Female Sex Hormones Female sex hormones are produced by the ovaries and various other tissues, such as the adrenal glands, pituitary gland, and placenta (during pregnancy). These female sex hormones are estrogen and progesterone. The primary source for estrogen is the ovaries. At puberty, estrogen stimulates enlargement of various accessory organs, which include the vagina, uterus, fallopian tubes, and external structures. Estrogen is also responsible for the development and maintenance 1-60 HM3F0161 ANUS SYMPHYSIS PUBIS URETHRA CERVIX RECTUM VAGINA VAGINAL ORIFICE LABIA MINORA LABIA MAJORA CLITORIS URINARY BLADDER UTERUS OVARY UTERINE TUBE Figure 1-61.—The female reproductive system.