How reproductive systems work
Hymens are often different from person to person. Most species have two sexes: But if someone's reproductive cells sustain DNA damage from radiation, this is a very different story. Reducing light alone may encourage egg laying by making the cage seem like a nestbox. Male Reproduction System National Standard: Closure 2 I hope that everyone enjoyed our class today. Other reproductive ruptures, infections and disorders.
This approach to reproduction results in fewer numbers of large young that spend the vulnerable portion of development inside the relatively safe refuge of mom's uterus until they are born ready to evade predators and competitors, enhancing their chance of survival. Shark embryos receive nutrients from several sources. Embryos can be nourished by solely the yolk, a form called lecithotrophic, or from the yolk and maternal nutrients, called matrotrophic. Gaining nutrients from mom is advantageous, giving the developing pup the opportunity to increase in size at birth therefore increasing survivorship.
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. Preformed vitamin A is found in foods from animal sources, including dairy products, fish, and meat especially liver.
By far the most important provitamin A carotenoid is beta-carotene; other provitamin A carotenoids are alpha-carotene and beta-cryptoxanthin. The body converts these plant pigments into vitamin A. Both provitamin A and preformed vitamin A must be metabolized intracellularly to retinal and retinoic acid, the active forms of vitamin A, to support the vitamin's important biological functions [ 2 , 3 ]. Other carotenoids found in food, such as lycopene, lutein, and zeaxanthin, are not converted into vitamin A.
The various forms of vitamin A are solubilized into micelles in the intestinal lumen and absorbed by duodenal mucosal cells [ 5 ]. Both retinyl esters and provitamin A carotenoids are converted to retinol, which is oxidized to retinal and then to retinoic acid [ 2 ]. Most of the body's vitamin A is stored in the liver in the form of retinyl esters.
Retinol and carotenoid levels are typically measured in plasma, and plasma retinol levels are useful for assessing vitamin A inadequacy. However, their value for assessing marginal vitamin A status is limited because they do not decline until vitamin A levels in the liver are almost depleted [ 3 ].
Liver vitamin A reserves can be measured indirectly through the relative dose-response test, in which plasma retinol levels are measured before and after the administration of a small amount of vitamin A [ 5 ].
For clinical practice purposes, plasma retinol levels alone are sufficient for documenting significant deficiency. A plasma retinol concentration lower than 0. In some studies, high plasma or serum concentrations of some provitamin A carotenoids have been associated with a lower risk of various health outcomes, but these studies have not definitively demonstrated that this relationship is causal. DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people.
These values, which vary by age and gender, include:. RDAs for vitamin A are given as mcg of retinol activity equivalents RAE to account for the different bioactivities of retinol and provitamin A carotenoids see Table 1. Because the body converts all dietary sources of vitamin A into retinol, 1 mcg of physiologically available retinol is equivalent to the following amounts from dietary sources: From dietary supplements, the body converts 2 mcg of beta-carotene to 1 mcg of retinol.
Currently, vitamin A is listed on food and supplement labels in international units IUs even though nutrition scientists rarely use this measure. However, for the manufacture and addition of preformed vitamin A and provitamin A carotenoids to dietary supplements and foods, as well as for labeling the vitamin A content of these products, the U. However, this RDA is also equivalent to 6, IU of beta-carotene from supplements, 18, IU of beta-carotene from food, or 36, IU of alpha-carotene or beta-cryptoxanthin from food.
So a mixed diet containing mcg RAE provides between 3, and 36, IU of vitamin A, depending on the foods consumed. Concentrations of preformed vitamin A are highest in liver and fish oils [ 2 ]. Other sources of preformed vitamin A are milk and eggs, which also include some provitamin A [ 2 ]. Most dietary provitamin A comes from leafy green vegetables, orange and yellow vegetables, tomato products, fruits, and some vegetable oils [ 2 ]. The top food sources of vitamin A in the U.
Table 2 suggests many dietary sources of vitamin A. The foods from animal sources in Table 2 contain primarily preformed vitamin A, the plant-based foods have provitamin A, and the foods with a mixture of ingredients from animals and plants contain both preformed vitamin A and provitamin A. DVs were developed by the FDA to help consumers compare the nutrient contents of products within the context of a total diet. Department of Agriculture's USDA's Nutrient Database Web site [ 10 ] lists the nutrient content of many foods and provides a comprehensive list of foods containing vitamin A in IUs arranged by nutrient content and by food name , and foods containing beta-carotene in mcg arranged by nutrient content and by food name.
Vitamin A is available in multivitamins and as a stand-alone supplement, often in the form of retinyl acetate or retinyl palmitate [ 2 ]. A portion of the vitamin A in some supplements is in the form of beta-carotene and the remainder is preformed vitamin A; others contain only preformed vitamin A or only beta-carotene.
Supplement labels usually indicate the percentage of each form of the vitamin. The amounts of vitamin A in stand-alone supplements range widely [ 2 ].
Multivitamin supplements typically contain 2,—10, IU vitamin A, often in the form of both retinol and beta-carotene. Adults aged 71 years or older and children younger than 9 are more likely than members of other age groups to take supplements containing vitamin A. Although these intakes are lower than the RDAs for individual men and women, these intake levels are considered to be adequate for population groups.
The adequacy of vitamin A intake decreases with age in children [ 4 ]. Furthermore, girls and African-American children have a higher risk of consuming less than two-thirds of the vitamin A RDA than other children [ 4 ]. Frank vitamin A deficiency is rare in the United States.
However, vitamin A deficiency is common in many developing countries, often because residents have limited access to foods containing preformed vitamin A from animal-based food sources and they do not commonly consume available foods containing beta-carotene due to poverty [ 2 ]. According to the World Health Organization, million preschool-aged children and In these countries, low vitamin A intake is most strongly associated with health consequences during periods of high nutritional demand, such as during infancy, childhood, pregnancy, and lactation.
In developing countries, vitamin A deficiency typically begins during infancy, when infants do not receive adequate supplies of colostrum or breast milk [ 13 ]. Chronic diarrhea also leads to excessive loss of vitamin A in young children, and vitamin A deficiency increases the risk of diarrhea [ 5 , 14 ].
The most common symptom of vitamin A deficiency in young children and pregnant women is xerophthalmia. One of the early signs of xerophthalmia is night blindness, or the inability to see in low light or darkness [ 2 , 15 ]. Vitamin A deficiency is one of the top causes of preventable blindness in children [ 13 ]. People with vitamin A deficiency and, often, xerophthalmia with its characteristic Bitot's spots tend to have low iron status, which can lead to anemia [ 3 , 13 ].
Vitamin A deficiency also increases the severity and mortality risk of infections particularly diarrhea and measles even before the onset of xerophthalmia [ 5 , 13 , 15 ]. In developed countries, clinical vitamin A deficiency is rare in infants and occurs only in those with malabsorption disorders [ 16 ]. However, preterm infants do not have adequate liver stores of vitamin A at birth and their plasma concentrations of retinol often remain low throughout the first year of life [ 16 , 17 ].
Preterm infants with vitamin A deficiency have an increased risk of eye, chronic lung, and gastrointestinal diseases [ 16 ]. In developed countries, the amounts of vitamin A in breast milk are sufficient to meet infants' needs for the first 6 months of life. But in women with vitamin A deficiency, breast milk volume and vitamin A content are suboptimal and not sufficient to maintain adequate vitamin A stores in infants who are exclusively breastfed [ 18 ].
The prevalence of vitamin A deficiency in developing countries begins to increase in young children just after they stop breastfeeding [ 3 ]. The most common and readily recognized symptom of vitamin A deficiency in infants and children is xerophthalmia. Pregnant women need extra vitamin A for fetal growth and tissue maintenance and for supporting their own metabolism [ 19 ].
The World Health Organization estimates that 9. Other effects of vitamin A deficiency in pregnant and lactating women include increased maternal and infant morbidity and mortality, increased anemia risk, and slower infant growth and development. Most people with cystic fibrosis have pancreatic insufficiency, increasing their risk of vitamin A deficiency due to difficulty absorbing fat [ 20 , 21 ]. However, improved pancreatic replacement treatments, better nutrition, and caloric supplements have helped most patients with cystic fibrosis become vitamin A sufficient [ 21 ].
Several studies have shown that oral supplementation can correct low serum beta-carotene levels in people with cystic fibrosis, but no controlled studies have examined the effects of vitamin A supplementation on clinical outcomes in patients with cystic fibrosis [ ]. This section focuses on three diseases and disorders in which vitamin A might play a role: Because of the role vitamin A plays in regulating cell growth and differentiation, several studies have examined the association between vitamin A and various types of cancer.
However, the relationship between serum vitamin A levels or vitamin A supplementation and cancer risk is unclear. Figs have been believed to increase fertility since the time of Ancient Greeks, and now we have scientific evidence. Figs contain a lot of iron, which are important for healthy eggs and ovulation. Oysters have been known to increase libido, but oysters can also be a great source for fertility because they are packed with zinc, which increases the production of good-quality eggs.
Any kind of berries are good at protecting eggs from damage and aging because they are full of antioxidants. Beans are a lean protein and are full of iron, which helps to increase fertility and libido. 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.