User:Student1017/Shark anatomy

Teeth
Shark teeth are strong and made of enamel. Many sharks have 3 rows of teeth. These teeth are embedded in the gums, not the jaw. Sharks are born with teeth that are constantly being replaced. Teeth are replaced every two weeks, approximately. The shape of the teeth determine the diet of the shark. For instance, a shark with flat teeth are used for crushing shellfish, pointed teeth are used for gripping fish, while the notoriously sharp teeth with jagged edge are used for large prey.

Internal Organs

 *  Liver-  The liver is a large and oily organ that comprises 25% of the total body weight of the shark . The two purposes of this organ in the shark are to store energy and oil. The liver is a hydrostatic organ. This organ helps with buoyancy since the liver stores oils, decreasing the density of the shark's body.
 *  Stomach-  The stomach terminates at the pylorus, that leads to the duodenum, and the to the spiral valve . The spiral valve is a coiled organ, it increases surface area so that nutrients can be absorbed . The spiral valve then empties into the rectum and anus, then into the cloaca.
 *  Pancreas-  This digestive gland passes secretions through the vental lobe and into the duodenum.
 *  Spleen 
 *  Rectal gland 

Skin
Unlike other fish, sharks do not have scales, but rather denticles. Denticle are made of layers of dentine and a surface of enamel, they are V-shaped. Riblets are sockets in the shark's skin which hold the denticles to reduce drag and friction. These denticles on the skin allow for the shark to move almost effortlessly, move faster, and move quietly. The skin of sharks is similar to the feeling of sandpaper, rough and abrasive.

Muscles
The red and white muscles are two muscles that sharks have for movement. The red muscles are used for "cruise control" or steady movement, while the white muscles are used for quick and sudden movements. Sharks, such as the Great White rarely use their muscles, they use as little energy as possible, and instead rely on their head and tail to guid their movements. Great White sharks use their heads to move by performing a back and forth motion of the head to create both high and low pressure areas throughout the rest of their body.

Temperature
Another way which helps sharks to move through the water effortlessly is partially due the regulation of their body temperature. Great white sharks, Shortfin Mako, Longfin Mako, Salmon Shark, and Porbeagle are endothermic, which helps them move quickly in water. They are able to regulate their body temperature depending on the temperature of the water the are in, in order to contract their muscles and swim faster. White sharks are often referred to as "cold-blooded killers," but they actually have the ability to warm their blood. Having the ability to keep their warmth helps them as predators as well. Another group of sharks, known as the mackerel sharks are able to warm their blood. These mackerel sharks retain their blood by using a heat exchange system called rete mirabile. The body temperature of mackerel sharks can be up to 10o higher than the surrounding water.