ENDOSKELETON: PARTS AND FUNCTIONS - BIOLOGY - 2024

An endoskeleton is a structure that supports the body of humans and some animals from the inside, allowing it to move and to structure and shape the body. Animals like fish, birds, and mammals have endoskeletons. In more complicated animals it serves as an anchor for muscle structures.

In a human being or in a crocodile, these muscles are anchored to the bones and interact with them to produce force, flex and perform all the daily tasks necessary to ensure the health and survival of the organism.

Image of different skeletons of animals.

Other animals (like sharks) develop very few bones and have endoskeletons made up largely of cartilage. They live their entire adult life with cartilaginous supports that leave no fossil record. These endoskeletons are generally more flexible than bone, but they are less resistant.

Endoskeleton and exoskeleton: differences

Branchiostoma lanceolatum. You can see the endoskeleton. Source: © Hans Hillewaert /

The endoskeleton grows as the body grows, allows easy attachment of muscles, and has many joints that provide flexibility. This makes it different from the exoskeleton in several ways.

Many insects and crustaceans have exoskeletons, which are hard, shell-like structures that cover the body from the outside. These structures are static, which means that they do not grow.

Animals with exoskeletons remain at a constant size throughout their lives or move into their old exoskeletons in order to generate entirely new ones as they grow.

In contrast, endoskeletons are permanent parts of vertebrate bodies. The endoskeleton begins to develop in the embryonic stage.

Animal bones are initially often made from cartilage, then over time they turn the bone through a process known as ossification. As the animal grows, the bones strengthen, thicken, and lengthen to full size.

Parts of an endoskeleton

The skeletal system of vertebrates is characterized by several easily identifiable parts. The first is the spine. All endoskeletons are built around a stacked spine of attached discs formed like a column that contains the animal's central nervous system.

At the top of the spine is a skull that houses the brain. The only exception to this rule is with echinoderms, which do not have skulls or brains. His movements are completely controlled by his central nervous system.

The limbs, fins, and any other limbs also extend from the spine. In most animals, the endoskeleton is covered in muscles, ligaments, and tissues.

These liners allow the endoskeleton to play an important role in body movement and motor control. The bone structure provided by the endoskeleton allows the body to stand, sit, bend and swim with precision.

Organ protection is an equally important endoscopic function. Vertebrate bodies are regulated by an intricate system of internal organs, including hearts, lungs, kidneys, and livers. The endoskeleton protects these organs from damage, protecting them with a "cage" of rib bones.

Most important functions

The main functions of the endoskeleton are:

-Provide support to the body and help maintain shape, otherwise the body will not be stable.

-Protect delicate internal organs, for example the rib cage that protects the heart and lungs from any damage

-It serves as a reservoir for calcium and phosphate in the body.

-Manufacture blood cells. Red blood cells are made in the bone marrow and this maintains a constant supply of blood cells.

-Allows the body to stand, sit, bend and swim with precision.

Endoskeleton advantages

The advantages include strong characteristics that support weight and even growth. Endoskeletons are generally found in larger animals due to better weight bearing, as exoskeletons can limit growth due to weight.

The main advantage would be that an endoskeleton can be used as a lever and anchor points for the muscles, which means that there is a biomechanical preeminence that is very important on our scale.

An ant or spider has a lot of strength relative to its size on its own scale, but if it were the size of a human being it could barely stand up because its musculature is confined within a rigid exoskeleton.

Also, it is much easier for a creature with lungs to have a flexible endoskeleton and rib cage, as it can easily take breaths without having to compress other organs.

Evolution

Lampreys

The earliest skeleton in the vertebrate lineage was a non-mineralized cartilaginous endoskeleton without collagen. It was associated primarily with the pharynx, in taxa such as lancets, lampreys, and witchfish.

After the evolution of collagen II, collagen-based cartilage could be formed. In contrast to animals that did not have collagenous skeletons, some of the early chondrichthyans (such as sharks) were able to form skeletal parts through the endochondral ossification process.

However, due to the lack of fossil records, the exact time of origin and the extent to which this mechanism was used is unclear.

From an evolutionary point of view, endochondral ossification is the youngest of the 2 types of bone formation (the oldest dermal bone was formed by intramembranous ossification).

It was produced in the skeletons of vertebrates by the replacement of cartilage templates. The endochondral ossification process evolved gradually, beginning with perichondral bone deposition using the molecular tools that had evolved during the evolution of bone shields in the skin.

This preceded the evolution of the processes of cartilage degradation and endochondral bone deposition, as shown mainly by studies on shark skeleton genesis. Endochondral ossification provided structural support for the development of vertebrate limbs.

With the advent of land vertebrates, skeletal function expanded in new directions. Although bone was still a reservoir for calcium and phosphorus, and acted as a shield for vulnerable parts of the body, it also began to serve as a site for blood cell production, and allowed for movement and mechanical support.

References

1. BBC Team (2014). Endoskeletons and exoskeletons. BBC. Recovered from: bbc.co.uk.
2. Darja Obradovic Wagner (2008). Where did bone come from ?. Institute of Chemistry and Biochemistry, Berlin University. Recovered from: archive.org.
3. Sarah Meers (2016). Endoskeleton & Exoskeleton. Study. Recovered from: study.com.
4. Wise Geek Team (2017). What Is an Endoskeleton ?. Wise Geek. Recovered from: wisegeek.com.