Female Reproductive System

Variations in the reproductive system

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Female Infertility Treatment, Causes and Diagnosis

Yolk dependency is found in Squaliformes, Hexanchiformes, Squantiformes, some Orectolobiformes and some Carcharhiniformes. At ovulation, yolk is deposited in the egg and that is the only amount the embryo will receive so they are typically small at birth. Oophagy, a form of nutrition found in species such as bigeye thresher, pelagic thresher, shortfin mako, and porbeagle sharks, evolved early in cartilaginous fish and allows the ovary to grow very large, over five kilograms, but the eggs are small, mm in diameter.

Most of the eggs that exist are for the nourishment of the developing embryos that rely on the yolk for only a short time period. The embryos, at about 5 cm, begin to ingest the other eggs by using temporary tooth structures.

Only a few fertilized eggs are produced early on in gestation, like the pelagic thresher that has only one per oviduct, with the exception of the sandtiger that has about Intrauterine cannibalism occurs when the embryo reaches about cm, seeks out other embryos, kills them by biting, grows larger and ingests the long dead embryo and feeding egg cases. The cannibal embryo ingests so much that it has a large, protruding yolk stomach.

All of the yolk consumed means these embryos are born relatively large, like the sandtigers' pups that are sometimes larger than one meter at birth, about one third the adult size.

Rays commonly demonstrate a method of nutrition delivery to their embryos by creating a placental analogue, something that acts like placenta. A part of the uterine lining secretes a nutritive substance called embryotrophe, which is ingested by the embryo. Placental viviparity refers to the method of nourishment that involves the yolk in the yolk sac and occurs only in the Carcharhiniforme order of sharks.

Within that order, placental viviparous species may share a family or genus with other species that are aplacental viviparous.

For example, the genus Mustelus has aplacental viviparous species such as the spotted estuary smooth-hound, gummy and starspotted smouth-hound sharks as well as placental viviparous species like dusky smooth-hound, and spotless smooth-hound.

The embryo ingests the yolk for the first few weeks and as it runs out, the sac gets long and thin, one side becomes vascularized with blood vessels and grows together with the uterine wall, creating a yolk sac placenta. All the nutrients in the mom's blood are then shared through the placenta, a nearly inexhaustible supply of energy. As long as mom's healthy, baby shark will be, too. This method of nourishment has evolved independently different times within the Elasmobranch group, resulting in the diversity of the structure.

Sharks deposit eggs through oviparity or give birth to live young through vivparity. Their fecundity, potential reproductive ability, ranges from a year to a possible produced by whale sharks. Studies done on tope and scalloped hammerhead sharks show that fecundity increases with overall body length of the female shark but that may not be a clear indicator.

Tough egg cases are laid on the substrate or attached to structures on the sea floor. The embryos within the cases are nourished by the yolk sac but those nutrients are limited so the young emerges small. Incubation in the case can last from a few months to more than a year.

Oxygenation and ventilation occurs through the slits in each side of the egg case as the embryo constantly fans its tail, increasing water flow. All eggs are laid in pairs and the development of the embryo is likely determined by the ambient water temperature. There is some evidence that the substrate upon which the eggs are laid is somewhat chosen by the mother.

Bullhead sharks have been observed picking up egg cases and wedging them into secure positions in the substrate. Viviparity is the mode of reproduction when the embryos remain in the uterus for all development. The embryo's nourishment can come from the yolk or the yolk can be supplemented by a connection to the mom. When there is no placental connection between mom and embryo but the embryo remains within the uterus for development, it is called aplacental viviparity, also referred to as ovoviviparity.

This type of development has three forms dependent on how the embryo is nourished. The embryo can be dependent on yolk only, nourished by other eggs in the uterus, or nourished through placental analogues.

The male reproductive system is complicated and involves many body structures: The testes, like in humans, are paired and symmetrical.

They are located at the top of the liver and are suspended by a fibrous sheath called the mesorchinum. Some species have embedded testes at the front end of the epigonal organ which is part of the shark's immune system.

Immature testes can be difficult to identify as they are only a mass of white tissue or a faint streak on the surface of the epigonal organ but adult testes are conspicuous and change throughout the year.

Testes are also involved in the creation and secretion of some steroid hormones. Spermatogenisis, when the immature cells become mature sperm cells, also takes place within the testes.

Elasmobranchs can have three different types of testes; radial, diametric, and compound testes. Radial testes, found in basking and lamniform sharks, are enclosed in the epigonal organ and the cells that will eventually become sperm begin development at the center of the lobe and proceed to the outer edge for further transport. Requim sharks of the family Carcharhinidae and hammerheads have diametric testes that protrude from the surface of the epigonal organ and the developing cells transport from wall to wall.

Compound testes are typically found in most batoids and shows a little of both the previous arrangements. The spermatocyst, the functional unit of shark testis, is a spherical form that contains spermatoblasts, which contain Sertoli cells, cells that nurture the developing sperm. The spermatocyst bursts and the Sertoli cells break up, releasing the sperm cells into the ductus deferns for storage. Claspers are paired tube-like copulatory organs that are formed from the median edge of the pelvic fins and serve to transport the sperm from male to female.

Immature claspers are small and flexible but mature claspers go through some calcification that hardens them and display some articulation with the pelvic fin base. In many studies, it is imperative to identify the life stage a shark is in and maturity is determined by the calcification and rigidity of the clasper and whether or not the rhipidion, the end of the clasper that contains the spur, can open.

Copulation occurs when the clasper is inserted and transfers the sperm. During copulation, the male determines which clasper to use by the way he has grasped the female. If he grips the females' right pectoral fin, he'll use his right clasper. Most copulatory studies indicate that sharks use only one clasper during mating but there is some evidence that species like the small spotted catshark may use both!

During mating the clasper is rotated forward and inserted into the female reproductive tract, held in place by a sharp spur. When the clasper is initially positioned forward, a new channel is formed between the one end of the clasper and a tube called the urogenital papillae of the male. The siphon sacs, paired muscular bladders on the bottom side of the male's body, contract and force sperm from the cloaca to the claspers and into the female by a current of seawater.

This flushing action created by the sacs may also serve to clear any other male gametes from the vicinity. Sperm travels as spermatophores, either round, ovoid, or tubular matrices that have a large number of sperm or sperm packets within them. Spermozeugma, globs of sperm, is embedded in the matrix of the spermatophores but are not encapsulated. These are temporary structures that vary greatly and little is understood about their function.

The Leydig gland is a branched tubular gland connected to the first part of the epididymis and contains cells for protein production, possibly accounting for the high levels of protein found in sharks' seminal fluid. The female reproductive anatomy has many familiar names, like ovaries and oviducts.

The ovaries can be either paired or single at the front end of the body on top of the liver and are responsible for the creation of germ cells, accumulation of yolk, and the creation and secretion of hormones.

More advanced forms of sharks have only a single ovary that is embedded in the front end of a long epigonal organ. An immature ovary is small and looks like a thin strip of granulated tissue but a mature ovary can be very large and bright yellow. Ovaries can either be characterized as being external or internal. External ovaries are compact and produce few large eggs, around mm diameter.

Internal ovaries, found in lamnid sharks, produces countless small eggs, mm diameter, that are fed to the oophagus embryos. In all sharks, oviducts are paired, tubular, and run the length of the body cavity on either side of the vertebral column. They are joined at the front end and terminate at the ostium where they curve into thinner tubes to the shell or oviduct gland aka the nidamental gland. The shell gland is well developed in mature females, much larger than the oviduct, and functions to secrete the egg membrane.

This gland may also play a part in sperm storage and fertilization as it becomes twice as large immediately after fertilization and during egg passage. The uterus is considered the back part of the oviduct where the embryonic shark develops. Typically, embryonic sharks are in contact with each other, however some carcharinid sharks and hammerheads keep their developing young in separate compartments. The vagina is the location of where the two uteri unite, opening up to the cloaca.

Elasmobranch eggs, or ova, are typically large with a lot of yolk which takes a lot of energy to produce so they usually aren't numerous. However, lamnid sharks do produce large numbers of small eggs, as mentioned above, to feed the growing embryos. The eggs are released from the ovary, pass through the ostium into the oviduct, usually two at a time, one into each oviduct. Oviparous sharks' shell gland produces a tough case for the long developmental period in the outside environment, ranging from several months to one year.

Viviparous sharks' case is thin and sheer. The eggs are telolecithal, the yolk concentrated at one end, because of their large size. A small part of the animal end of the egg is involved in the cleavage process and the other end becomes the yolk sac.

Low iron levels can result in anovulation, which is when ovulation does not produce a healthy egg. Dark leafy greens such as spinach, romaine, arugula, and broccoli are high in folate, a B vitamin that has been shown to improve ovulation. Maca root increases fertility in men and women by increasing energy, boosting the immune system, and providing vital minerals and nutrients.

Maca Root is packed with iron and iodine. Eating up to three servings a day of fresh fruits and vegetables is important for any diet, but especially important when trying to conceive.

Soy contains a compound very similar to estrogen which can cause estrogen levels to be too high and can negatively affect fertility. Consuming refined sugar, such as high fructose corn syrup, can cause blood sugar spikes which can negatively affect the reproductive system as well as the rest of the body.

Any unidentified sensitivities can negatively impact fertility, as well as cause headaches, heartburn, gas, bloating and weight gain. Blood tests, such as those provided by Nutritional Healing , observe white blood cells in the presence of common foods. If the blood cells enlarge, burst or shrink when combined with a food, this indicates a sensitivity.

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