Shark Anatomy & Physiology
Sharks have been around since before dinosaurs roamed the Earth. During the past 70 million years, sharks have remained virtually unchanged in their anatomy and physiology. These fearsome fish live in every ocean. The size of sharks varies, but their anatomy is consistent. Some sharks are small enough to fit in a large aquarium, whereas the whale shark can grow up to 50 feet long. Most sharks grow to about the size of a human.
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Skeleton
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Human skeletons are composed of bone, but the shark's skeleton is made completely of cartilage. Cartilage is a strong and durable substance, more flexible than bone. This flexibility helps the shark move fluidly though the water and turn on a dime. The light weight of the shark's skeleton keeps it from sinking.
Teeth
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Sharks have up to 3,000 teeth at any given time. When you look at a photo of a shark's mouth, you see several rows of teeth. According to Seaworld.org, sharks go through up to 30,000 teeth in a lifetime because their teeth aren't permanent. Shark teeth are attached to a membrane called the tooth bed. The tooth bed works like a conveyor belt. As a shark grows, new teeth move forward, replacing the older outer row of teeth. Sharks use the large outer row of teeth to bite, so these teeth eventually get damaged or worn out.
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Skin
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The small rough teeth-like scales of shark skin feel like sandpaper if stroked backward from tail to head, but the shark is relatively smooth if stroked from forward from head to tail. Shark scales are called dermal denticles, which means "tiny skin teeth." The dermal denticles are shaped like a tooth, larger at the top and then narrowing to a point in the direction of the tail.
Liver
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Sharks have very large livers, comprising up to 25 percent of their total body weight and filling up most of their body cavity. The shark liver has two jobs. It stores the fatty reserves, providing a source of energy for the shark. The liver also helps a shark float by storing oils that are lighter than water, making the shark more buoyant. According to Cancer.org, shark liver oil is rich in alkylglycerols, compounds that may have anti-cancer properties.
Gills
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Sharks have five to seven gills on each side of their head to filter oxygen from the water. Water flows through a shark's mouth and also over the top of the gills. Tiny blood vessels in the gills absorb oxygen from the water. Excess water is released through the gill slits. In order to breathe, some species of sharks need to move forward all the time or rest in a current of flowing water.
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References
- Photo Credit shark 2 image by cherie from Fotolia.com
