What does tendons do

The main task of these components is to maintain the structure of the tendon and facilitate the biomechanical reaction of the tissue against mechanical loads. The main substance in tendons and ligaments is basically about 0.

The most effective of inorganic substances are proteoglycans. In addition to prostaglandins with a small amount in the main substance, the most common biomechanical properties are the decorin and cartilage oligomeric matrix protein COMP [ 10 ]. The protein clusters in the structure are connected to a large portion of the extracellular matrix of tendons, making the matrix a structure similar to the gel. Thanks to this compound, collagen provides spaces and lubrication between microfibrils, while cement-like material also makes the collagen structure of tendons stable and contributes to the resistance of the tissue [ 3 , 11 , 12 ].

Collagen Type-I fibers are capable of withstanding large tensile loads and are found in abundance from the tendon structure, allowing a certain degree of stretch and mechanical deformations of the tendons [ 13 ]. This synthesis process is similar to that of all connective tissue, although it may differ slightly depending on the type of complex collagen.

Therefore, tendons, which contain Type-I collagen, have a process of synthesis and degradation similar to those in the ligaments and bones. From here, with a more detailed look, we can say that synthesizing for collagens in tendon structure begins in the cell membrane of the tenocytes.

In other words, the integrins are like force sensors and, in particular, detect cell withdrawal, allowing the cell to react to these mechanical stimuli. At the same time, various growth factors contribute to the regulation of this mechanical conversion process [ 14 ].

Cross-linkages form between collagen molecules, which are very important for clustering at the fibril level. The cross-links between the fibrils are more complex. And this cross-link structure of collagen fibrils provides the strength of the tissue and thus ensures that it performs the task of the tissue under mechanical loads.

In the newly formed collagen, these cross bonds are less in number, soluble in salt or acid solution, and can easily break with heat. As collagen matures, the number of cross bonds that can dissolve and break down decreases and decreases to the minimum level. As a result, organized collagen molecules form microfibril, sub-fibrils, and fibrils. The fibrils are also clustered to form collagen fibers, collagen clusters or fascicles, and the tendon.

Tenocytes are arranged between these fascicles and aligned in the direction of the mechanical load [ 10 ]. In the cellular structures of tendons, as mentioned above, there is much less amount of elastin than collagen, because the mechanical properties of the tendons depend not only on the architecture and properties of collagen fibers but also on the extent to which this structure contains elastin.

Because the bond has a special function and the nerve roots of the spine, mechanical stresses, stresses, etc. Blood circulation in tendons is very important, because the current circulation of blood directly affects metabolic activity especially during healing. Therefore, they have a white color when compared to the muscles with a much higher blood vessel density.

However, there are a few factors such as the anatomical location, structure, previously damaged condition, and physical activity level of tendons that contribute to blood supply besides the small amount of vascular structure. There are studies that show that blood flow increases in tendons in the case of increasing physical activity in the literature. There are more vascular tendons due to their anatomical position or shape and function.

The flushing of tendons is primarily derived from the synovium at the point of attachment to the bone or paratenon. However, some tendons feed on the tendon like the Achilles tendon and the paratenon structure, and some tendons are fed by a true synovial sheath they are surrounded. Bone and tendon adhesion is a layer of cartilage where blood flow cannot pass directly from the bone-tendon compound. Instead, they make anastomosis with the veins on the periosteum and make indirect connections [ 16 ].

In contrast, tendons have a very rich neural network and are often innervated from the muscles in which they are associated or from the local cuticle nerves. However, experimental studies on humans and animals have shown that tendons have different characteristics of nerve endings and mechanoreceptors. They play an important role especially for proprioception position perception and nociception pain perception in joints.

In fact, studies have shown that there is internal growth in the nervous and vascular systems during the healing of tendon, which causes chronic pain. Internal growth of the vein is an indicator of the tendon trying to heal, but because of this growth, nerves may feel pain in areas without pain before.

This means that the nerves play an important role not only in the proprioception but also in the nociception. Nerve endings are located below the muscle-tendon junction and typically in the bone-tendon junction in the form of Golgi organs, Pacini bodies, and Ruffini endings.

Of these, the Golgi organs are only mechanically stimulated by pressure and compression, so that they receive information from the power produced by the muscle. Pacinian bodies are rapidly adaptive mechanoreceptors due to nerve endings with a highly sensitive capsular end to deformation, thus dynamically responding to deformation, but are insensitive to constant or stable changes.

Ruffin termination results from multiple, thin capsule-tipped, and single axons and has slowly adapting mechanoreceptors and thus continues to receive information until a constant warning level is stimulated during deformation [ 17 ]. The tendons are surrounded by loose, porous connective tissue, which is called paratenon. A complex structure, paratenon, protects the tendon and allows shifting tendon cover format.

Tendon sheaths consist of two continuous layers: parietal on the outside and visceral on the inside. The visceral layer is surrounded by synovial cells and produces synovial fluid. In some tendons, the tendon sheath extends along the tendon, while in others it is found only in the binding parts of the bone.

The parietal synovial layer is found only under the paratenon in the body regions where tendons are exposed to high friction. This is called the epitenon and surrounds the fascicles. In regions where friction is less, tendon is surrounded by paratenon only. At the tendon-bone junction, the collagen fibers of endotenon continue into the bone and become a peritendon.

The regions of the tendon bonding to the bone consist of a dense connective tissue, which is able to adhere to the hard bone from the dense connective tissue and is resistant to movement and damage. Although they occupy a small area in size, the areas of adhesion to the bone have a complex structure that is much different from that of the tendon itself. According to the size of the load they carry, they show a different proportion of collagen bundles [ 18 ]. The tendons cling to the bone is a complex event; collagen fibers mix into fibrocartilage, mineralize, and then merge with the bone.

Sticking to the bone is done in two ways. In the first type, the adhesion of many collagen fibers is direct to the bone, while the second type indirectly adheres to the periosteum. In other words, the tendon is attached to the bone in the form of fibrous or indirect adhesion to the metaphysics and diaphysis of long bones or fibrocartilaginous or direct adhesion to the epiphyses of the bone. In fibrous adhesions, while the collagen fibers of the tendon are permanently adhered to the periosteum during bone development, fibrocartilaginous adhesions have a gradual transition from tendon to bone.

This gradual transition in fibrocartilaginous adhesions includes the tendon, decalcified fibrocartilage, calcified fibrocartilage, and four zones of bone, so that the uniform distribution of the load at the adhesion site and the joint movement and the coordination of the collagen fibers are ensured. However, changes in the fibrocartilaginous structure due to compressive loading vary depending on the adhesion sites of the tendons.

This ensures better protection against compressive forces. The bones of the tendons are composed of four regions within the bone; at the end of the tendon region 1 , collagen fibers enter the fibrocartilage fibrous cartilage—region 2.

As the fibrocartilage progresses, it becomes mineral fibrocartilage area 3 and then integrates with cortical bone fourth region. This transformation, which is more bone structure than tendon structure, leads to gradual increase of mechanical properties of the tissue [ 3 , 19 , 20 , 21 ].

In general, they pass through the joints and adhere to their distal. In this way, they increase the effectiveness of the muscles on the joints. At the same time, similar to bones, mechanical properties vary depending on the load carrying place. For this reason, knowing where they are helps us understand the structure.

In fact, not every muscle has a tendon. While some tendons are involved in some muscles that play an active role in joint movements, the presence of some tendons is to increase muscle movement distances rather than the movement of the joint. For example, Achilles tendon is a very special tendon for the body carrying the loads by centralizing the strength of a few muscles.

In contrast, some tendons, such as the posterior tibial tendon, act by distributing the load to several bones. Although it is known that most tendons originate from the muscle and adhere to the bone, some tendons may be the starting point for muscles, or two muscles are connected to each other through a tendon [ 22 , 23 ]. They can be very small and very long, and they can be very large and very short.

Tendons are very variable according to their shape, long, round, rope-shaped such as Achilles tendon , or short; flat tissue adhesion such as bicipital aponeurosis can be seen. In other words, tendons may change from flat to cylinder, from fan shape to ribbon shape. However, round tendons such as flexor digitorum profundus or flat tendons such as rotator cuff, bicipital aponeurosis are more involved in the body.

In this simple classification, tendons are divided into round and flat and are very different from each other as structural and functional. For example, while round tendons respond equally to tensile loads with parallel collagen patterns, flat tendons such as rotator cuffs can respond microanatomically in the form of compression and shear forces due to longitudinal, oblique, and transverse collagen sequences.

Symptoms of tendonitis include pain when the muscle is moved and swelling. The affected muscle may feel warm to the touch. Telling the difference between a ligament or tendon injury on your own can be hard. Whenever you have pain and swelling, see your doctor for a skilled diagnosis and effective treatment plan. Doctors recommend:. But others are. Take these precautions to protect your tendons and ligaments:. There are thousands of ligaments and tendons throughout the body.

Ligaments and tendons are both made of connective tissue and both can be torn or overstretched, but they differ in function. Ligaments attach one bone to another. Tendons attach a muscle to a bone. Both, however, are essential to proper body mechanics. Recognizing ligament and tendon problems before they become major injuries is key to enjoying an active and pain-free life.

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