Sharks don’t breathe through their noses, but instead through slits on the sides of their heads called gills. But how exactly does this work? Tap or click on hotspots to find out.


Sharkopedia : Shark Physiology |

Did You Know?

Sharks Need To Maintain Their Salt Levels

Because most sharks live in a saltwater environment, they must maintain a balance between the salt in the water and in their bodies. If the balance is off, it could lead to the shark having either too much or not enough water in its body - either imbalance can quickly lead to death.

Sharks have far more salt in their bloodstream than most vertebrates - about 250 times as much, or close to the same concentration as seawater. This allows them to stay in perfect "osmotic" balance with the surrounding seawater.

To maintain this balance, sharks secrete a salty compound called urea, which flows through their system to maintain a balance between the salt in the water and in their bodies. A shark's kidneys play an important role in this process. If sharks build up too much urea, they can excrete the salty excess from an opening below their abdomen called a "cloaca" or through their gills.

A few sharks, like bull sharks, have developed "super kidneys" that can remove large amounts of urea from the bloodstream. This allows them to enter and hunt in freshwater rivers and lakes, where salt levels are far below seawater.

Sharkopedia : Shark Physiology |

Did You Know?

Whether Sharks Sleep Is Still A Mystery

The question of whether or not sharks sleep is still a mystery. Sleep itself, in fact, is something scientists still haven't fully figured out. They suspect sharks likely don't sleep the same way we do, but that sharks may experience a form of rest that serves the same function.

Oxygen-rich water must flow over a shark's gills in order for it to breathe, but some sharks have figured out that they can rest motionless in caves or other locations where there's a current. They're still conscious - their eyes will follow divers swimming by, for example - but they're definitely not in active mode. Some sharks don't even need current; they can pump water over their gills using their cheeks, allowing them to remain otherwise motionless.

A study on spiny dogfish (a small shark) showed that a shark's swimming movements are coordinated primarily in the spinal column, not the brain. This would seem to suggest that if a shark were to briefly shut down its conscious brain activity while in motion, it would still be able to swim. So perhaps even a swimming shark can take a quick nap.

Sharkopedia : Shark Physiology |

Spotlight On Anatomy

How Do Sharks Move Oxygen From Here To There?

A shark's gills extract oxygen from water and bring it inside the body, but once it's there, how does it get to the rest of the shark?

Sharks don't have lungs to store oxygen, so a shark's blood must deliver the oxygen throughout the body. This process starts in the gills. There, small capillaries in the gills allow oxygen to enter the bloodstream. The oxygenated blood is then pumped directly to the head and the rest of the body.

This pumping is controlled by the shark's heart. After blood has traveled throughout the body, it enters the heart. From there, it's pumped directly to the gills, where carbon dioxide is dumped and oxygen is picked up, and the whole process starts all over again.

A shark's heart is S-shaped and is composed of four compartments. Together, these regulate the heart's contraction rate and squeeze blood through the circulatory system while preventing it from washing back.

Sharkopedia : Shark Physiology |

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Shark Physiology