Shark Internal Anatomy – Part 1

We all know that sharks are pretty amazing, but why? What are their secrets?
Well, let’s find them out today and explore a shark’s internal anatomy


Sharks are fish that have no bones, only cartilage. Cartilage is flexible and durable, yet it is about half the normal density of bone. It allows them to go up and down quickly in the ocean without a lot of effort to stay afloat. The flexibility in cartilage allows them to bend much easier than bony fish, this elasticity also gives them more speed as their tails can move faster to propel them through the water.

Dermal Denticles

Shark skin is covered with millions of tiny teeth called dermal denticles. These point backwards, reducing surface drag and helping the shark to swim faster. As a shark grows they shed their denticles, replacing them with larger ones. This hydrodynamic efficiency of shark skin had been replicated by swimming costume manufacturers with the aim to improve swimmer speeds. In fact, they were so effective that they were labelled “technology doping” and banned from Olympic competition. The denticles vary in shape according to the species and where they are on the body. Some are so big that the shark uses them as defensive spines or shields!

Photo taken by White Shark Projects volunteer, Mikaela Cauble


Shark teeth are made of enamel, are strong and appear in huge numbers in the fossil record. Sharks defend themselves immediately after birth, so they are born fully equipped. They have many rows of teeth which are constantly being replaced. Ensuring they always have a full set of razor- sharp pearly whites. Sharks replace their teeth approximately every 2 weeks and some species, like the Great White Shark, can lose 60,000 teeth in their lifetime! We can tell what a shark eats by the shape of its teeth. Flat crushing teeth are perfect for eating shellfish, pointed teeth for gripping fish and sharp serrated teeth for larger prey, such as seals. The teeth may change with age as the diet of a pup may differ to that of an adult.


Fins provide balance and stability in the water. Sharks have a large dorsal fin which provides balance. Usually they’ll also have a smaller dorsal fin further back towards their tail. The shark’s pectoral fins are used to steer and lift themselves in the water and their tails are used to propel themselves forward. The size and shape of a shark’s fins and tail can vary greatly. Faster sharks, such as the Shortfin Mako, tend to have shorter half moon shaped tails. Whereas, slower moving sharks, such as the Broadnose Sevengill Shark, have longer thinner tails. Sadly, high demand for shark fins has contributed to the decline of many shark species.

Photo taken by White Shark Projects volunteer, Mikaela Cauble


To breathe many shark species have to remain in constant forward motion. As they swim water is driven through their mouth and out over their gills – a process known as ‘ram-ventilation’. As water passes over the gills, oxygen is absorbed into tiny blood vessels and transported around the body. Yet, some less active sharks (such as shysharks and Zebra Sharks) have got around this problem. They are able to spend lots of time lazing around by sucking water into their mouth and squeezing it over their gills.


Incredibly, a shark’s liver can make up to 25% of their total body weight! In mammals this is only 5%. Their huge oily liver helps them to maintain buoyancy in the water, along with their fins and lightweight cartilaginous skeleton. Unfortunately, there is a huge demand for shark liver oil, which is used in cosmetics. So, this adaption that’s so integral to their survival, also makes them vulnerable to human exploitation.

Puffadder Shyshark

Puffadder Shyshark – photograph by Andy Murch –


Sharks have 2 types of muscle – red and white. Red muscle works by breaking down the fat in the shark’s body. It has a good blood supply and helps the shark swim for long periods of time. Whereas, white muscle works by using energy from the breakdown of glycogen (sugars), enabling sharks to make short fast sprints when catching prey or escaping danger. Long bundles of muscle fibres run from the top of a shark’s head to the tip of its tail. When these contract, a series of movements are produced along the body. This enables the shark to propel itself through the water with its tail. More noticeable muscle contractions produce faster speeds. However, to conserve energy, sharks will build up speed with a series of muscle contractions, then stiffen their body to cruise through the water.

This article sums up just how awesome sharks are, but luckily it’s not everything! Keep posted for more amazing information!

Written by Kimberley Deumer

Published 7th October 2019

Read our previous blogs for more information on these magnificent creatures!

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