Tendon

Bones and muscles are the basis of our skeleton and they provide the basic framework for our body. Tendon, ligament, cartilage are some of the important tissues that provide the framework to our body. Here we will learn more about the tendon, what is the function of tendons, and the role of tendons in the human body. Collagen is a basic structural and functional component of a tendon. They transfer the mechanical forces of muscle contraction to the bones. 

What is a Tendon?

Tendon tissue is also known as sinew. It is a band of fibrous connective tissues. Tendons join muscles to bones. It is also capable of withstanding tension. Tendon is made up of collagen and thus they are similar to the ligaments. Just one function that differentiates between tendon and ligament is that tendons join muscle to bones whereas ligament connects bone to bone. They are very strong and are thus able to withstand the tension that is generated by muscular contractions. This is because of their parallel orientation and the composition of tissue fibres in the tendon. 

Tendon Structure

As we read above about what is a tendon and that it is made up of dense connective tissue. In tendons, there are specialized fibroblast cells that are known as tenocytes that are the main component of their cellular matrix. The dry mass of tendons makes up 30-40% of their total mass which is further composed of 60-75% collagen 1, 2-10% collagen 3, and around 2% collagen 4. Collagen 1 is the main component of the collagen in tendons. The tenocytes are responsible for synthesizing the extracellular matrix of tendons. Tendons can also be called tendon connective tissue. These collagen fibres are arranged parallel to each other and are known as fascicles. Endotendineum is a loose connective tissue that contains thin collagen fibrils and these individual fibres are bound to it. Epitenon helps in binding the group of fascicles. Fascia encloses the whole tendon. Paratenon is responsible for filling the space between tendon tissue and fascia. Paratenon is fatty areolar tissue. Sharpey’s fibres are responsible for anchoring healthy tendons to bones. Proteoglycans help is holding the collagen in the tendon together. Proteoglycan is a compound that is made up of glycosaminoglycan groups that are bonded to proteins. These proteoglycans are woven together with collagen fibrils. Associations between the fibrils are thought to be formed by dermatan sulfate whereas chondroitin sulfate is thought to be involved in occupying the fibrils. The tendon diagram is shown below. 

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                                                    Figure: Tendon and its sub-parts

Tenocytes

These cells are solely responsible for producing collagen molecules. These collagen molecules further aggregate to produce collagen fibrils. These collagen fibrils are then organized into fibres and the tenocytes are present between them at the ends. Here it forms a three-dimensional network between the cell processes and collagen in the tendon. Gap junctions are responsible for the communication between cells. By doing so, it gives them the ability to respond and detect mechanical stress. There are no nerve fibres in the internal tendon bulk. Nerve endings are present in epitenon and paratenon. At the junction of tendon and muscle fibres, Golgi tendon organs are present. In every person, the length of the tendon varies. Thus, this length of tendon is responsible for determining the actual and potential size. Tendons are of shorter length in bodybuilders whereas in athletes tendons are generally younger. Genetics is responsible for determining the length of the tendon. Environmental factors are not responsible for determining the length of the tendon. But muscles can be affected by environmental factors. 

Tendons Function

In the above paragraphs, we read about the meaning of the tendon and its structure. Now we will learn about the tendons function. The functions of tendons are listed below. 

• Tendon help is transmitting the forces because of their mechanism by which tendons connect bones to muscles. 

• During locomotion, this connection helps the tendon to modulate forces.

• There are some energy-storing tendons that store energy and at high efficiency can recover the energy. 

• The collagen fibre’s diameter and orientation help in determining the mechanical properties of the tendon. 

• Due to the absence of hydroxyproline and proline, the collagen fibres have some flexibility. 

• The collagen fibres in tendons allow them to resist the tensile strength whereas proteoglycan allows them to resist compressive stress. 

Conclusion

From the above passages we can conclude that tendons hold very much importance in forming our body structure. They are responsible for connecting muscle to bones and thus they provide mechanical support and strength to the bones. The tendon is made up of tenocytes. Tendons function by making a connection with the bones and transmitting their forces.