What Are They?
The ovaries are multipurpose organs. They harbour, nurture, and guide the development of the egg so that when it is extruded from the ovary (ovulation) it has been prepared for its migration down the fallopian tube, its penetration by sperm, and its eventual implantation in the wall of the uterus. Additionally, the ovary is a sophisticated endocrine structure. It secretes hormones essential for the onset of menstruation (menarche) and its cyclical perpetuation. At the same time, the ovary produces profound alterations in body physique that transform a prepubertal girl into a mature woman.
The mature ovary is a roughly bean-shaped structure weighing about 14 grams. It, like the adrenal gland, consists of an outer cortex and a central medulla with the addition of an inner hilus (depression or pit) that serves as the point of entry and exit of blood vessels and nerves. The ovaries are located in the pelvis, attached to a structure called the broad ligament (see the reproductive system.)
Immature follicles (primordial follicles) embedded in fibrous tissue (stroma) enlarge as the follicle matures and moves through the cortex toward the outer surface of the ovary. The cells lining the follicle multiply and become layered into a zona granulosa. Along with this change the stromal cells immediately surrounding the follicle arrange themselves concentrically to form a theca (an enclosing sheath). This egg-containing mature structure is known as a Graafian follicle. Both granuloma cells and thecal cells secrete steroid hormones known as estrogens. The follicular fluid bathing the ovum is an extraordinarily complex liquid containing not only high concentrations of estrogens but also other steroids (progestogens and androgens), pituitary hormones (FSH, LH, prolactin, oxytocin, and vasopressins), and numerous enzymes and bioactive proteins.
 During the maturation (follicular) phase of the menstrual cycle, follicles continue to enlarge until one (or, rarely, two) follicles rupture at the ovarian surface. The egg is extruded and promptly enters the fallopian tube to begin its journey to the uterus. The supportive role of the follicle does not end with the discharge of the egg. Thecal cells penetrate the emptied follicle and, together with persisting but modified granulosa cells, fill the follicle, now called a corpus luteum, which is the source of serum progesterone during the postovulatory (progestational or luteal) phase of the menstrual cycle. With menstruation, the corpus luteum becomes scarred and contracted (atretic), remaining as a corpus albicans. In the event that the extruded egg is fertilized and pregnancy ensues, the corpus luteum persists and continues to secrete increasing amounts of progesterone during the first trimester. As might be expected, these changes are controlled by secretions from the hypothalamus and the anterior pituitary gland.
Before the onset of puberty the ovaries are quiescent, and the stroma of the cortex and medulla are studded with multiple primordial follicles. Puberty is heralded by subtle but far-reaching changes. Some undefined event stimulates the secretion of luteinizing hormone-releasing hormone (GnRH) from the hypothalamus, and GnRH secretion becomes pulsatile. Animal studies support the notion that puberty is precipitated by a reduction in the secretion of melatonin, a hormone of the pineal gland. There is, however, no evidence that melatonin has a role in the onset of puberty in humans.
Secretion of GnRH activates gonadotrophs from the anterior pituitary, resulting in enhanced secretion of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The secretion of these hormones, particularly LH, is much enhanced shortly after the onset of sleep; increased nocturnal secretion of LH is the earliest change detectable in the pubertal child. It appears that GnRH secretion is inhibited by neurons that secrete dopamine and is stimulated by noradrenergic neurons (involved with norepinephrine). Endogenous opiates, especially beta-endorphin and dynorphin, also play important roles in regulating the frequency and strength of GnRH secretion.
The increased secretion of estrogens from the ovaries, stimulated by LH secretion coupled with maturing Graafian follicles (resulting from the increased FSH secretion) leads to menarche. Before long, the cyclic activity characteristic of the normal female hypothalamus appears. Immediately following the cessation of menstruation, the sequence begins with a gradual rise in the blood level of estradiol (the most potent of the estrogens), paralleled by a slow rise in serum LH. An inconspicuous rise in androgens also occurs while progesterone and its precursor, 17-hydroxyprogesterone, remain suppressed. Finally, the rising estradiol level trips off a mid-cycle surge of LH and FSH (an example of a positive feedback mechanism). The abrupt rise in gonadotropins precipitate ovulation, ending the follicular phase. With the formation of the corpus luteum, estrogen levels fall but not back to baseline, while the levels of 17-hydroxyprogesterone and progesterone are much elevated. At the end of the luteal phase all hormonal levels return to baseline, and the withdrawal of the estrogens precipitates the next menstrual period. The normal menstrual cycle is 28 days long although it varies considerably from one woman to another and occasionally in the same woman, with irregularities occurring most frequently shortly after puberty or before the menopause.
The premenstrual fall in levels of estrogen and progestins occurs because of a degeneration and loss of function of the corpus luteum (luteolysis) that results from a faltering of LH pulses from the pituitary. The endometrium, which had become increasingly thickened and vascular, undergoes a constriction of small arteries. Cutting off oxygen and nutrient supplies to the endometrial lining leads to cell death and the subsequent sloughing and bleeding characteristic of menstruation. It should be noted that the basal body temperature, which fluctuates only mildly during the follicular phase, shows a rather abrupt progressive rise after ovulation, paralleling the increase in progesterone. This thermogenic action results from the effect of the elevated progesterone levels on temperature-regulating centres in the base of the brain. (The structural and functional changes that occur in the fallopian tubes [oviducts], lining of the uterus [endometrium], distal opening to the uterus [cervix], and vagina and that accompany the endocrinologic fluctuations are discussed in the reproductive system. The extension and accentuation of these changes, which occur in the event of pregnancy, are also discussed there.)
Hormones
As is the case in the adrenal cortex, the parent sterol from which all ovarian steroid hormones are formed is cholesterol. Both estrogens and progestogens are synthesized from a common precursor, pregnenolone, itself formed from cholesterol. These chemical sequences also include dehydroepiandrosterone, androstenedione, and testosterone, all of which are steroids that are primarily androgens (male sex hormones).
Once secreted into the blood, estrogens share with androgens, particularly testosterone, a binding globulin (testosterone-estradiol-binding globulin, TeBG), which transports them to target tissues. At this site, the estrogens easily penetrate the cell surface and are bound to an intracellular binding protein. It is in this form that they are transported to the cell nucleus, where they modulate protein synthesis by influencing the formation of DNA.
Estradiol, the most potent of the three major estrogens, is formed by both granulosa and thecal cells, perhaps acting together. Estrone can be formed from estradiol, but its major precursor is androstenedione. Estriol is formed from both estrone and estradiol and is the weakest of the estrogens. Indeed, in some circumstances estriol appears to have anti-estrogen effects; that is, it may bind to tissue estrogen receptors without setting in train estrogen effects and, while doing so, block the receptor from access to more potent estrogens such as estradiol. It has been suggested that it protects against the development of breast cancer in women. Catechol estrogens are metabolic products that also have anti-estrogen effects.
The progesterones (progestins) are formed by the corpus luteum. Progesterone is also produced by the adrenal cortex, but the rise that occurs in its serum level during the luteal phase stems from ovarian secretion. The hormone 17-hydroxyprogesterone is secreted by thecal cells and accounts for most of the hormone found in the blood; again, the adrenal cortex may secrete a lesser amount at a constant rate.
Among the many nonsteroidal substances secreted into the follicular fluid is a substance called inhibin (folliculostatin), which is secreted by granulosa cells (and by Sertoli cells in the male). The primary action of inhibin is to inhibit the secretion of pituitary FSH. Since the major action of FSH is to stimulate the formation and function of granulosa cells, the relationship between inhibin and pituitary FSH represents a classical negative feedback servomechanism. Relaxin, a polypeptide hormone produced by the corpus luteum, induces a relaxation of the pubic ligaments connecting the two halves of the pelvis, an action that mitigates the discomfort of a woman in labour and eases the passage of the child. Finally, the ovary contains both oxytocin and vasopressin in high concentration, which serve a paracrine function. Oxytocin may assist in the expulsion of the egg from the ovary and may also mediate the process of luteolysis (break up of the corpus luteum). Vasopressin constricts local blood vessels after the egg is extruded.
Ovarian hormones have multiple functions. Pulsatile secretion of LH occurs well before the onset of the first menses (menarche) so that the rate of estrogen secretion also increases progressively. This results in the progressive development of breasts (thelarche) and the appearance of pubic hair and culminates in the menarche. Estrogens, including those contained in oral contraceptives, also exert ongoing generalized effects in the adult female. They mildly impair the body's ability to metabolize glucose, and they tend to increase the level of fats (triglycerides) in the blood. These effects are easily obviated by other endocrine adjustments in the normal woman, but they have an impact when these compensatory mechanisms are impaired. Estrogens increase the serum concentration of a large number of binding proteins that transport other materials; these include binding proteins for cortisol, thyroxine, iron, and copper, as well as those that bind estrogens and testosterone (TeBG). Finally, estrogens tend to increase the concentration of sodium, and therefore the degree of water retention, again particularly in susceptible women.
 The ovaries, in addition to producing egg cells (ova), secrete and are acted upon by various hormones in preparation for pregnancy.
Prevention and Treatment of Ovarian Dysfunction
The following reflexes may be active when the ovaries are involved:
These reflexes should be tested and treated with the proper supplementation.
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