All About Sharks
Staying Alive: How A Shark's Parts Work
In order to survive underwater and find prey, sharks rely on a variety of physical traits and processes. From breathing to staying afloat to tracking down food, find out what it takes to keep a shark alive.
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.
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.