Ovarian follicles

Female sexual development and behaviour in mammals occurs by default and requires no ovarian secretion, and it is only in genetic males that the testis can secrete hormones which destroy this female pattern and superimpose that of the male. Sexual differentiation is not so well defined in fish, and larval exposure to both synthetic estrogens and androgens is widely used in aquaculture to produce monosex cultures. Endocrine disruption of sexual differentiation in fish may therefore reflect both the complexity and diversity of such processes between different species. Some care is required in use of the terms hermaphrodite and sex-reversal since a true hermaphrodite has both functional testes and ovaries and a sex-reversed fish is fully functional as its final sex—both produce the appropriate viable gametes. Such functional sex-reversal is not possible in mammals, but in some species of fish it is the normal developmental pattern. In most of the cases of hermaphroditism or sex-reversal reported in the non-scientific press, there is evidence only for a few ovarian follicles within a functional testis. This may be considered as feminisation or a form of intersex, and is very clearly endocrine disruption, but it is certainly neither sex-reversal nor hermaphroditism. In some cases the terms have even been used to infer induction of a single female characteristic such as production of yolk-protein by males. 

The estrogens are secreted by the ovarian follicle and in smaller amounts by the adrenal cortex. Estrogens are important in the development and maintenance of the female reproductive system and the primary and secondary sex characteristics. At puberty, they promote growth and development of the vagina, uterus, fallopian tubes, and breasts. They also affect the release of pituitary gonadotropins (see Chap. 50). 

Progesterone is secreted by the corpus luteum, placenta, and in small amounts by the adrenal cortex. Progesterone and its derivatives (ie, the progestins) transform the proliferative endometrium into a secretory endometrium. Progestins are necessary for the development of the placenta and inhibit the secretion of pituitary gonadotropins, which in turn prevents maturation of the ovarian follicle and ovulation. The synthetic progestins are usually preferred for medical use because of the decreased effectiveness of progesterone when administered orally. 

Ovaries Turner s syndrome Gonadal dysgenesis Premature ovarian failure Chemotherapy/radiation Lack of ovarian follicles Other genetic anomalies Early loss of follicles Gonadal toxins... 

The pathophysiologic changes that occur during the perimenopausal and menopausal periods are caused by the decrease and eventual loss of ovarian follicular activity. As women age, the number of ovarian follicles decreases, and the remaining follicles require higher levels of FSH for maturation and ovulation. During perimenopause, FSH concentrations... 

Corpus luteum The small yellow endocrine structure that develops within a ruptured ovarian follicle and secretes progesterone and estrogen. 

Verheyen, G., J. Helsen, and E. Decuypere. 1990. Accumulation of zinc in egg yolk ovarian follicles and organs after forced resting by high dietary zinc. Brit. Poult. Sci. 31 147-154. 

Kilic-Okman T, Kucuk M, Altaner S (2003) Comparison of the effects of letrozole and clomiphene citrate on ovarian follicles, endometrium, and hormone levels in the rat. FertilSteril 80 1330-1332... 

Homeostasis of tissues Hematopoietic system (M9) Ovarian follicle atresia (Kl) Remodeling of endometrium during menstruation (Tl)... 

A separate protein hormone produced primarily in the testis, called inhibin, also affects the secretion of FSH. Inhibin has been isolated primarily from testicular extracts but also may be found in the antral fluid of ovarian follicles in females. Inhibin decreases the release of FSH from the pituitary but does not affect hypothalamic production of GnRH. 

Contraceptive. An agent that diminishes the likelihood of or prevents conception. Corpus luteum. A yellow glandular mass in the ovary formed by an ovarian follicle that has matured and discharged its ovum. If the ovum has been impregnated, the corpus lu teum increases in size and persist for several months. 

These hormones are essential for the maintenance of pregnancy. The only natural progestin hormone, progesterone (3.38), is produced by the corpus luteum, an endocrine tissue formed in the ovary by the ruptured ovarian follicle after the level of luteinizing hormone peaks. If pregnancy occurs, the corpus luteum persists for the first three months of the pregnancy after that, its role is taken over by the placenta as the major... 

In females, the target organs are the ovaries where it increases the number and size (maturation, development and ripening) of Graafian follicles and prepare them for ovulation. During its development, the ovarian follicles secrete its own hormone estrogen. In males, it stimulates spermatogenesis. Under the influence of this hormone, seminiferous tubules produce spermatozoa. 

Complete development of the ovarian follicles to secretory stage and secretion of estrogen. 

Promotes the final maturation of ovarian follicles and ovulation and the formation of corpus luteum which secretes progesterone. 

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