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Female Reproductive System Physiology

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Male reproductive system

Following ovulation in all vertebrates, the ovary may become smaller, become modified for maintenance of pregnancy , or proceed to form additional eggs. The process of ovulation in vertebrates has been documented, but the immediate causes remain to be clarified. It is almost certain that an ovulatory hormone is secreted by the pituitary gland i.

It is highly probable that breakdown of very small fibres that bind the follicular cells together may occur at the stigma, weakening the follicular wall at that location. Hormones from the ovary and other sources may play a role, as may neurohormones, which are hormones released at nerve endings. Rhythmic contractions of the entire ovary occur at ovulation in many vertebrates and have been described in rabbits.

The role of mechanical pressure within the follicle, however, is not understood. Ovulation in most mammals spontaneous ovulators occurs cyclically as a result of the spontaneous release of the ovulatory hormone. In a few mammals reflex ovulators the stimulus of copulation is essential for release of the ovulatory hormone.

Striking postovulatory changes take place in the follicles of mammals and, to lesser degrees, of lower vertebrates. Blood vessels from the theca interna invade the ovulated follicles; the granulosa cells divide, enlarge, accumulate fats, and obliterate any remnants of the collapsed antra. Thereafter, they are known as lutein cells. Theca interna cells undergo changes identical to those of the granulosa cells.

The result in mammals is the formation of solid masses called corpora lutea , recognizable as prominent reddish-yellow bulges on the ovary. Corpora lutea produce the hormone progesterone , which is essential for the maintenance of pregnancy. The conversion of postovulatory follicles into structures more or less resembling mammalian corpora lutea has been demonstrated in numerous viviparous reptiles, amphibians, and elasmobranchs; in certain other fishes, including cyclostomes; and in some oviparous amphibians and reptiles.

In birds, the postovulatory follicle shrinks, and identifiable corpora lutea do not develop, although some granulosa cells accumulate lipids of unknown significance. The female reproductive tract consists of a pair of tubes gonoducts extending from anterior, funnel-like openings ostia to the cloaca, except as noted below. The gonoducts are specialized along their length for secretion of substances added to the eggs; for transport, storage, nutrition, and expulsion of eggs or the products of conception; and, in species with internal fertilization, for receipt, transport, storage, and nutrition of inseminated sperm.

The predominately muscular tracts are lined by a secretory epithelium and ciliated over at least part of their length. Fusion of the caudal tail ends of the paired ducts may occur.

Gonoducts are absent in cyclostomes and a few gnathostome fishes that have abdominal pores. A few vertebrates have only one functional gonoduct. Gonoducts in lungfishes and amphibians are coiled muscular tubes that are ciliated over most of their length. Only occasionally do they unite caudally in a genital papilla before opening into the cloaca.

During breeding seasons their diameter increases severalfold because of the highly active secretory epithelium. Between breeding seasons they are small. In some anurans frogs, toads , such as Rana , the lower end of each gonoduct is expanded to form an ovisac, in which ovulated eggs are stored until spawning; the tube between the ostium funnel-like opening and ovisac is the oviduct.

In viviparous amphibians the young develop in the ovisac. In amphibians, numerous multicellular glands extend deep into the lining of the female tract. Six successive glandular zones have been described in some urodeles, and these secrete six different gelatinous substances upon the egg. Female urodeles often have convoluted tubular outpocketings of the cloaca called spermatheca; they temporarily store sperm liberated from the male spermatophore.

The two gonoducts of elasmobranchs share a single ostium, a trait found only in Chondrichthyes. The ostium is a wide caudally directed funnel supported in the falciform ligament, which is attached to the liver. The role of the fimbria of the ostium at ovulation has been described see above Ovaries. Two oviducts pass forward from the ostium to the septum transversum i. Approximately midway between ostium and uterus each oviduct has a shell nidamental gland.

Fertilization takes place above the shell gland, which may be immense or almost undifferentiated. Half of the shell gland secretes a substance high in protein content albumen , and the other half secretes the shell—delicate in viviparous forms, thick and horny in most oviparous species. Horny shells may have spiral ridges and many long tendrils, which entwine about an appropriate surface after the egg is deposited.

In the viviparous shark Squalus acanthias several eggs pass one after the other through the shell gland, where they are enclosed in one long delicate membranous shell that soon disintegrates. Beyond the shell gland the oviducts terminate in an enlargement, which, in viviparous species, serves as a uterus.

An oviducal valve may be found at the junction of oviduct and uterus. Although the two uteri usually open independently into the cloaca, they occasionally unite to form a bicornuate two-horned structure. In immature females, the uterus may be separated from the cloaca by a hymen, or membrane. The tract enlarges enormously during the first pregnancy and does not thereafter fully regress to its original size. The gonoducts of most lower ray-finned fishes resemble those of lungfish, but those of gars and teleosts are exceptional in that the oviducts are usually continuous with the ovarian cavities.

A median genital papilla receives the oviducts in teleosts, and the papilla is sometimes elongated to form an ovipositor. European bitterlings deposit their eggs in a mussel by means of the ovipositor, and female pipefish and sea horses deposit them in the brood pouch of a male.

With certain modifications, the gonoducts of reptiles and birds are comparable to those of lower vertebrates. Crocodilians, some lizards, and nearly all birds have one gonoduct; the other is not well developed.

Even in birds of prey having two functional ovaries, the right oviduct is sometimes undeveloped. The tracts of reptiles generally show less regional differentiation than do those of birds. The oviduct funnel ostium in birds forms the chalazae—two coiled, springlike cords extending from the yolk to the ends of the egg.

In both reptiles and birds, much of the length of the female tract is oviduct. This region, called the magnum in birds, secretes albumen; lizards and snakes do not form albumen. Behind the albumen-secreting region is a shell gland. In lizards, the gland is midway along the tract.

In birds, the shell gland is at the posterior end, has thick muscular walls, and is often inappropriately called a uterus. It is preceded by a narrow region, or isthmus, which secretes the noncalcareous, or soft, membranes of the shell. The shell gland leads to a narrow muscular vagina that empties into the cloaca.

The vagina secretes mucus that seals the pores of the shell before the egg is expelled. Special vaginal tubules spermatheca store sperm over winter in some snakes and lizards; seminal receptacles have been described in the oviduct funnel in some snakes. In birds, sperm storage glands sperm nests often occur in the funnel and at the uterovaginal junction.

In lizards and birds, ovulation does not usually occur into a tract already containing an egg. Some lizards shed very few eggs per season; the gecko, for example, sheds only two. The female reproductive tracts of monotremes, the egg-laying mammals, consist of two oviducts, the lower ends of which are shell glands. These open into a urinogenital sinus, which, in turn, empties into a cloaca.

Marsupials have two oviducts, two uteri duplex uterus , and two vaginas. The upper parts of the vaginas unite to form a median vagina that may or may not be paired internally. Beyond the median vagina, the vaginas are again paired lateral vaginas and lead to a urinogenital sinus.

The posterior end of the pouchlike median vagina is separated from the forward end of the urinogenital sinus by a partition. When the female is delivering young, the fetuses are usually forced through the partition and into the urinogenital sinus, bypassing the lateral vaginas.

The ruptured partition may remain open thereafter, resulting in a pseudovagina. It closes in opossums, and in kangaroos both the median and lateral routes may serve as birth canals. The lateral vaginas in marsupials receive the forked tips of the male penis. Fertilization in all mammals takes place in the oviducts Fallopian tubes. In eutherian mammals i. Fallopian tubes often have a short dilated ampulla, or saclike swelling, just beyond the ostium. Implantation of the egg occurs only in the uterine horns; the embryos become spaced equidistant from one another in both horns even if only one ovary has ovulated.

In some species one horn is rudimentary—the left in the impala an African antelope —and the embryos become implanted in the other horn, even though both ovaries ovulate. The body of the uterus in some mammals e. In other mammals ungulates, many cetaceans, most carnivores and bats the body of the uterus has one chamber into which the two horns empty bicornuate uterus.

There are numerous intermediate conditions between the bipartite and bicornuate condition. Apes, monkeys, and man have no horns, and the Fallopian tubes empty directly into the body of the uterus simplex uterus. In all mammals, the uterine body tapers to a narrow neck cervix. The opening os uteri into the vagina is guarded by fleshy folds lips of the cervix.

The vagina in eutherian mammals other than rodents and primates terminates in a urinogenital sinus that opens to the exterior by a urinogenital aperture.

In some rodents and in higher primates the vagina opens directly to the exterior. In the young of many species a membrane, the hymen, closes the vaginal opening. In guinea pigs the hymen reseals the opening after each reproductive period. Sperm are stored over winter in the uterus of some bats and in vaginal pouches in others. One pair usually opens into the urinogenital sinus or, in primates, into a shallow vestibule at the opening of the vagina.

Prostates develop as buds from the urethra in many female embryos but often remain partially developed. They become well developed, however, in some insectivores, chiropterans, rodents, and lagomorphs, although their function is obscure.

A variety of glands labial, preputial, urethral are found in the mucosa, or mucous membrane. Glands in the uterine mucosa provide nourishment for embryos before implantation. Cervical uterine glands secrete mucus that lubricates the vagina, which has no glands. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind. Your contribution may be further edited by our staff, and its publication is subject to our final approval.

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Accessory glands Accessory sex glands that are conspicuous outgrowths of the genital tract are almost uniquely mammalian. Female systems Ovaries Ovaries lie within the body cavity and are suspended by a dorsal mesentery mesovarium , through which pass blood and lymph vessels and nerves.

Tracts The female reproductive tract consists of a pair of tubes gonoducts extending from anterior, funnel-like openings ostia to the cloaca, except as noted below. Previous page Male systems. Page 9 of Next page Adaptations for internal fertilization. Learn More in these related Britannica articles: Human reproductive system , organ system by which humans reproduce and bear live offspring.

Provided all organs are present, normally constructed, and functioning properly, the essential features of human reproduction are 1 liberation of an ovum, or egg, at a specific time in the reproductive cycle, 2 internal fertilization of the….

The functions of the individual organs of reproductive systems are fairly uniform throughout the primates, but, in spite of this physiological homology, there is a remarkable degree of variation in minor detail of organs between groups—particularly in the external…. The testes of mammals descend from the abdominal cavity to lie in a compartmented pouch termed the scrotum. In some species the testes are permanently scrotal, and the scrotum is sealed off from the general abdominal cavity.

In the polychaetes, sexes are usually separate but cannot be distinguished in the immature state until gametes eggs and sperm appear. Gametes are derived from the mesodermal linings around the digestive tract.

The developing gametes are shed into the coelom, where they are nourished…. The masses of sex cells that compose the gonads of crinoids fill special cavities in the arms or pinnules. Crinoids are the only echinoderms with gonads outside the main body cavity, probably because its volume is reduced. Asteroids typically have 10 gonads, two…. More About Animal reproductive system 15 references found in Britannica articles Assorted References annelids In annelid: Reproduction echinoderms In echinoderm: Reproductive system mollusks In mollusk: Reproduction and life cycles In mollusk: The reproductive system arthropods In arthropod: Reproductive system and life cycle arachnids In arachnid: Reproductive system scorpions In scorpion: Internal features spiders In spider: Reproductive system insects lepidopterans In lepidopteran: Abdomen and genitalia cirripedes In cirripede: The reproductive system View More.

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Female systems