Shark+Urogenital

The urogenital system is made up of the uinary and reproductive systems. The purpose of the urinary system is to purify the body of its Nitrogenous waste. Both the male and female urinary system work similarly. Before veiwing the urinary system you must first **remove the digestive system and associated organs.** It may look like there is little left at first, but the urinary system is made up of mainly small tube structures. The process begins as the **Kidneys**, located along the dorsal side of the shark and run the full length of the shark’s body. It is here at the **Kidneys** that Nitrogenous waste is removed from the blood and prepared for excretion. As the organ heads toward the tail, it begins to enlarge. The kidney is known as an opisthonephros type, in that it develops the entire length of the holonephros. The part of the **kidney** that is closest to the head does not serve a major function in the urinary system. For females, it is considered useless, while in males, it is simply an accessory gland for sexual reproduction. As for the actual excretion of the waste removed from the blood, the female Dogfish possess a tube that carries the waste from the kidneys to the cloaca. This tube is known as the **Archinephric Duct**. Although this tube is also found in the male, it is not used for the same purpose as in the female (urinary function), but rather used for sexual reproduction. It will be talked about later in this section. Instead of an **Archinephric Duct** to transport the waste from the **Kidney** to the cloaca, males instead have developed an **Accessory Urinary Duct**. The part of the kidney, which serves a function in the female dogfish, is known as the **Nephron**. The **Nephron** forms a cuplike structure known as **Bowman’s Capsule**. A series of capillaries (**Glomerulus**) runs through **Bowman’s Capsule**, releasing waste from the blood into the **Kidneys**. From here it continues its path to the cloaca for excretion. Also part of the urogenital system is the reproductive system. The female reproductive system begins in the **ovaries**. The **ovaries** are where the egg or ova is produced and are located on the caudal dorsal side of the shark, just next to the liver. **Cut open one of the ovaries and notice the yellow colored eggs.** Every egg is enveloped in a follicle.The color is a result of the large amount of yolk in each ovum. From here, the ovum leaves the **ovary**, heading for the **oviduct**. The **oviduct** is a tube-like structure where the ovum is fertilized by the male sperm. It is clearly visible in mature females due to its large size. The **oviduct** is connected directly to the cloaca, allowing for sperm to pass directly to the ovum. Different areas of the **oviduct** have been shown to perform different functions. One area of the **oviduct** that has been enlarged (distal to the **ovaries**) is knows as the **nidamental gland**. This gland has been shown to store sperm for great lengths of time to allow for fertilization later, a highly efficient method of reproduction. The **oviduct** thins out again, only to enlarge once more in a more caudal location to form what is known as the **uterus**. The **uterus** is the location of embryonic development. **To discover where the oviducts open into the cloaca cut through the left wall of the cloaca and continue through the wall of the colon.** The opening should be located towards the dorsal portion of the cloaca. The male reproductive system begins in the **testes**. These sex organs are located in the same spot as the **ovaries** in the female (dorsal side of the shark next to the liver); however, the **testes** are noticeably larger than the **ovaries**. The size of the **testes**, however, varies in size depending on the month of the year (they are larger during the breeding months of January and February). The function of the **testes** is to produce sperm that will later be used to fertilize the female ova. The sperm is taken from the **testes** to the **Archinephric Duct** by few small tubes known as **Ductuli Efferentes**. The **Archinephric Duct** transports sperm to the **Seminal Vesicle**. The **Seminal Vesicle** is directly attached to the spiralled **Archinephric Duct** and is noticeably larger and straight. The **Seminal Vesicle** leads to the **Sperm Sac**. The **Sperm Sac** is the last stop before excretion in the male reproductive system. The **Sperm Sac** contains seminal fluid that will allow the sperm to pass safely to the female and fertilize the ova. The entire embryonic developmental stage occurs in the female. For this reason, males must have developed certain structures that allow them to fertilize the female egg (equivalent to the male penis). This structure is known on the Spiny Dogfish as the **Clasper**. The **Clasper** allows the male shark to hold on to the female shark during sexual reproduction. Each **Clasper** posses a **Clasper Groove**, allowing the **Clasper** to bend at possible awkward angles, should this be necessary during sexual reproduction. Also part of the **Clasper** structure is the **Siphon Sac**. All of these structures are essential during sexual reproduction. To start off sexual reproduction, the **Siphon Sac** absorbs some seawater. This seawater will help to propel the seamen from the male into the female. Once the seawater is absorbed, the clasper muscles contract to allow for an alignment between the apopyle and urogenital papilla. Once this occurs, the male Dogfish then sticks his **Clasper** into the female cloaca. The **Siphon Sac’s** muscular wall contracts and forces the seawater and semen into the female. This then travels up the **oviduct** to where the ova are with the intention of fertilization. The development of the embryos will end up in the uterus for around 22 months. The dogfish live in salt water and possess porous skin, as a result fresh, unsalted water wants to diffuse into the ocean and the ocean's salt water wants to diffues into the shark.This isn't good since the shark will loose fresh water which it needs. To eliminate the problem of such water loss, sharks have evolved so that they contain more salt then the surrounding water. Due to such a characteristic, if the shark was to swim into fresh water it could possibly have kidney failure as the kidneys would have to work harder to get rid of the excess water.The regulator for this osmoregulation system is the foul smelling molecule trimethylamine oxide(TMAO).