Difference Between Endoskeleton and Exoskeleton

What is an Endoskeleton?

Derived from the Greek word ‘endon’, which means ‘inner’ or ‘within’, and ‘skeletos’, which means skeleton. An Endoskeleton is a framework of rigid and hard tissues, also known as bones inside an organism’s body. The Endoskeleton supports the structure and also protects the vulnerable organs and internal tissues.

A lot of vertebrates (an animal which possesses a backbone or a spinal column) like mammals, reptiles, amphibians, birds, and fishes have an endoskeleton that is constituted of tissues in the form of bones and cartilages. 


Functions of the Endoskeleton

The first and foremost function of the Endoskeleton is to protect and support the body. Without an endoskeleton, the body would have no shape whatsoever, and for e.g., a human would not be able to stand up on its own. The axial skeleton, which is made up of the skull, the rib cage, and the vertebral column, performs the function to protect the fragile organs like the heart, the liver, the kidneys, and the lungs. The appendicular skeleton is made up of the legs and feet, the arm bones, the pelvic girdle, and the shoulder blades, which support the structure and protect the limbs. 

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What is an Exoskeleton? 

An exoskeleton is a hard surface that covers the exterior of most animals, known as the invertebrates (an animal which lacks a backbone, for e.g., arthropod, mollusk, annelid, coelenterates, etc.).

Just like the Endoskeleton in mammals and other animals, the exoskeleton helps the body by supporting and protecting them. The hard and rigid exoskeleton also provides protection from predatory animals. Also, the waterproof feature of an exoskeleton makes sure that the moisture is removed from the surface of the animal, hence protecting it and acting as a barrier. 


Functions of the Exoskeleton

An exoskeleton is made up of tissues, which adds to the strength and rigidness of the exoskeleton. The functions of an exoskeleton are remarkably similar to that of an endoskeleton. It protects the animals from attacks by unseen creatures so that the soft organs inside them do not get damaged. Chitin is the most important component of the exoskeleton in the insects, which protects them. Different types of exoskeletons are The Arthropod Cuticle, the shell, and the molting. 


Difference Between Endoskeleton and Exoskeleton in Humans

  • The Endoskeleton of an animal is present inside the body, which is also known as the internal skeleton. Meanwhile, the exoskeleton of an animal is present outside the body, which is also known as the external skeleton. 

  • The exoskeleton is made up of hard bones and malleable cartilage. Meanwhile, the exoskeleton is made up of scales, cuticles, and shells formed by the chitin tissue. 

  • The Endoskeleton is mainly found inside of vertebrates, which are mammals, birds, fishes, amphibians, and reptiles, whereas the exoskeleton is found inside of invertebrates like insects, spiders, crabs, centipedes, and millipedes. 

  • The Endoskeleton is made up of the endoderm (the innermost layer of cells of an embryo during the early development stage) and is a living structure. Meanwhile, the exoskeleton is made up of the ectoderm (the outermost layer of cells of an embryo during the early development stage) and is a non living structure. 

  • The Endoskeleton of animals grows with the body throughout their lives, and it does not molt. Whereas the exoskeleton does not grow with the body, it remains the same but goes through a shedding phase, known as molting. 

FAQ (Frequently Asked Questions)

Question: How does the Endoskeleton Help in Movement?

Answer: The Endoskeleton, which is made up of bones, helps the body to move when the muscles are attached to them. This function is known as a movement. The muscle tissues are attached to the bones with the help of tendons and ligaments. As the bones are basically rigid and provide support to the body with the help of their strength, the movement of the skeleton is possible because of the connecting bones known as the joints. The different types of joints allow the body to move in various ways. For example, the ‘ball and socket’ joints of the hip and shoulders are made up of a spherical ball that fits inside the socket, and it moves in all the directions. The ‘pivot’ joint, which is found in the elbows, and the vertebrae under the skull, helps in movement by allowing the bones to move in rotation.

Question: How is Homeostasis Related to the Endoskeleton?

Answer: The process of regulation of calcium levels in the body is known as homeostasis. The Endoskeleton of a body is made up of mostly bones, which consist of 99% of the body’s calcium. Through homeostasis, the levels of calcium can be controlled accordingly with the help of the thyroid gland. When the blood calcium levels of the body increase rapidly and become too high, the hormone calcitonin is secreted by the thyroid gland, which lowers the calcium levels. Whereas, when the body calcium levels decrease and are very low, the thyroid gland releases a hormone called parathyroid, which increases the blood calcium levels.

Question: What is Chitin?

Answer: The exoskeleton of insects is made up of a huge, structural polymer component known as Chitin. It is found in the hard cell walls of invertebrates. This precious substance can form hard and solid structures on its own like insect wings and also can also combine with calcium carbonate to form the hard surface structure known as the shells. The flexibility that Chitin provides the arthropods helps them develop flexible and strong wings and has also helped them evolve in many species. Also, because of the Chitin polymer properties in the shells, it protects the crabs and other invertebrates from predators. The rigid wall structure protects and maintains the shape of the creatures.