A tendon or sinew is a strong fibrous connective tissue tape that typically connects the muscles to the bones and is able to withstand tensions.
Tendons are similar to ligaments; both are made of collagen. Ligaments join one bone to another, while the tendon connects muscles to bones and muscles to the muscles for proper body function and movement
Video Tendon
Structure
Histologically, the tendon consists of an ungodly dense regular connective tissue encased in a dense, irregular connective tissue sheath. A healthy normal tendon consists mostly of collared parallel composite collagen fibers. They are anchored to the bone by Sharpey fibers. The dry mass of the normal tendon, which forms about 30% of their total mass, comprises about 86% of collagen, 2% elastin, 1-5% proteoglycans, and 0.2% inorganic components such as copper, manganese, and calcium. The collagen portion consists of 97-98% type I collagen, with a small number of other types of collagen. These include type II collagen in the cartilaginous zone, type III collagen in reticulin fibers from blood vessel walls, type IX collagen, type IV collagen in capillary basement membrane, V type collagen in blood vessel walls, and X-type collagen in mineralized fibrocartilage near the interface with bone.
Collagen fibers converge into macroaggregates. After secretion of the cell, cleaved by procollagen N- and C-proteinase, and the tropocollagen molecule spontaneously converge into insoluble fibrils. A collagen molecule has a length of about 300 m and a width of 1-2 nm, and the diameter of the fibrils formed can range from 50-500 nm. In the tendon, the fibrils then converge further to form a fascist, which is about 10 mm long with a diameter of 50-300 m, and eventually become a tendon fiber with a diameter of 100-500 m. Fascicles are bound by endotendineum , which is a fine loose connective tissue containing thin collagen fibrils. and elastic fibers. The wicked group is limited by epitenon . Filling the interstitia inside the fascia where the tendon is located is paratenon a network of fatty areolar.
Collagen in the tendon is held together with proteoglycan components including decorin and, in the area of ​​tendon compression, aggrecan, which is able to bind collagen fibrils at specific locations. Proteoglycans intertwined with collagen fibrils - their glycosaminoglycan side chains (GAGs) have many interactions with fibril surfaces - suggesting that proteoglycans are structurally important in fibrill interconnection. The main components of GAG from the tendon are the dermatization of sulfate and chondroitin sulphate, which are associated with collagen and are involved in the process of fiber assembly during the development of the tendon. Sulfate dermatics are thought to be responsible for forming associations between fibrils, whereas chondroitin sulfate is considered more involved with the volume of hoarding between fibrils to keep them separate and help resist deformation. The side chain of the sulfate density of the decoration aggregate in solution, and this behavior may be helpful with collagen fibril assembly. When decorin molecules are bound to collagen fibrils, their dermatic dermatic chains can prolong and connect with other dermatic dermatric chains in decorations bound to separate fibrils, thus creating interfibril bridges and ultimately causing parallel alignment of fibrils.
Tenocytes produce collagen molecules, which combine end-to-end and side-to-side to produce collagen fibrils. Fibril bundles are arranged to form fibers with a tightly elongated tenocyte between them. There is a network of three-dimensional cell processes associated with collagen in the tendon. The cells communicate with each other through the junction gap, and this signal gives them the ability to detect and respond to mechanical loading.
Blood vessels may be visualized in endotendons that run parallel to collagen fibers, with occasional branching of transverse anastomosis.
The internal tendon tendon is considered to contain no nerve fibers, but epitenones and paratenons contain nerve endings, while Golgi tendon organs are present at the junction between the tendon and muscle.
The tendon length varies in all major groups and from person to person. The long tendon, in practice, determines the actual and potential muscle size. For example, all other relevant biological factors are the same, a man with shorter tendons and longer bicep muscles will have greater potential for muscle mass than men with longer tendons and shorter muscles. Successful bodybuilders will usually have shorter tendons. In contrast, in sports that require athletes to excel in actions such as running or jumping, it is beneficial to have longer than average Achilles tendon and shorter calf muscles.
The tendon length is determined by genetic predisposition, and has not been shown to either increase or decrease the response to the environment, unlike muscles, which can be shortened by trauma, using imbalances and lack of recovery and stretching.
Maps Tendon
Function
Traditionally, the tendon has been considered a mechanism that connects muscles to the bones as well as the muscles themselves, functioning to transmit forces. This connection allows the tendons to passively modulate forces during movement, providing additional stability without active work. However, over the past two decades, many studies have focused on the elastic properties of some tendons and their ability to function as springs. Not all tendons are required to perform the same functional role, with most positioning limbs, such as fingers when writing (positional tendons) and others acting as springs to make locomosi more efficient (vein energy storage). The energy storage tendon can store and recover energy with high efficiency. For example, during a human step, the Achilles tendon extends as an ankle dorsiflex joint. During the last part of the step, when the leg of the plantar-flexes (pointing radius down), the stored elastic energy is released. Furthermore, because the tendon extends, the muscle can function with less or even no change in length, allowing the muscles to produce greater strength.
The mechanical properties of tendons depend on the diameter and orientation of collagen fibers. Collagen fibers are parallel to each other and packed tightly, but show a wave-like appearance due to planar undulation, or wrinkling, on a scale of several micrometers. In the tendon, collagen fibers have some flexibility due to the absence of hydroxyproline and proline residues at specific locations in the amino acid sequence, allowing the formation of other conformations such as internal curves or loops in the triple helix and resulting in the development of curly hair. Wrinkles in collagen fibrils allow the tendon to have flexibility as well as low compression stiffness. In addition, since the tendon is a multi-stranded structure consisting of many independent fibrils and wickers, it does not behave as a single rod, and this trait also contributes to its flexibility.
The tendon proteoglycan component is also important for mechanical properties. While collagen fibrils allow the tendons to withstand tensile stress, proteoglycans allow them to withstand the compressive stress. These molecules are highly hydrophilic, meaning that they can absorb large amounts of water and hence have a high swelling ratio. Because they are bound non-covalently to the fibrils, they can invert connect and separate themselves so that the bridge between the fibrils can be broken down and reformed. This process may be involved in allowing the fibrils to extend and lower the diameter under pressure. However, proteoglycans also have a role in tendon tensile properties. The tendon structure is effectively a fiber composite material, built as a series of hierarchical levels. At each hierarchical level, collagen units are bound together by collagen crosslinks, or proteoglycans, to create structures that are highly resistant to tensile loads. Elongation and collagen fibril strains alone have been shown to be significantly lower than the total extension and strain of all tendons under the same amount of stress, suggesting that the proteoglycan rich matrix must also be deformed, and the matrix rigidity occurs at high strain levels. This non-collagen matrix deformation occurs at all levels of the tendon hierarchy, and by modulating the organization and structure of this matrix, different mechanical properties required by different tendons can be achieved. The energy storage tendons have been shown to harness significant amounts of shear between the wasik to allow for the high strain characteristics they require, while positional tendons are more dependent on shear between collagen and fibril fibers. However, recent data suggest that energy storage tendons can also contain a wicked twisted, or helical, in nature - a setting that would be very useful to provide the spring-like behavior required in this tendon.
Mechanics
Tendons are viscoelastic structures, meaning they exhibit elastic and viscous behavior. When stretched, the tendon exhibits a typical "soft tissue" behavior. The force-extension, or stress-strain curve begins with a very low stiffness region, since the straightening crimp structure and collagen fibers parallelly show a negative Poisson ratio in the tendon fibers. Recently, tests conducted in vivo (via MRI) and ex vivo (through mechanical testing of various cadaveric tendon tissues) have shown that healthy tendons are highly anisotropic and show negative (auksetic) Poisson ratios across multiple planes when stretched to 2% along its length, ie within its normal range of motion. After this 'toe' region, the structure becomes more rigid, and has a linear strain-to-stress curve starting to fail. The mechanical properties of tendons vary greatly, as they match the functional requirements of the tendon. Tendons store energy tends to be more elastic, or less rigid, so they can more easily store energy, while positional tendons tend to be less viscoelastic, and less elastic, so they can provide better motion control. Typical energy storage tendons will fail at about 12-15% of strain, and pressure in the region of 100-150 MPa, although some tendons may be expanded than this, for example a shallow digital flexor on a horse, which extends in excess of 20% when galloping. Positional tendons can fail in strains as low as 6-8%, but can have moduli in the 700-1000 MPa region.
Several studies have shown that the tendon responds to changes in mechanical loading by growth and remodeling processes, such as bone. In particular, one study showed that the absence of Achilles tendon in rats resulted in a decrease in the average thickness of collagen fiber bundles consisting of tendons. In humans, an experiment in which people are subjected to a simulation of microclimate environments finds that tendon stiffness decreases significantly, even when subjects are asked to do the reliever exercises. These effects have implications in many areas ranging from bedridden patients to more effective design exercises for astronauts.
Healing
The tendons in the legs are complex and complicated. Therefore, the healing process for the tendon is broken long and painful. Most people who do not receive medical care within the first 48 hours of the injury will suffer from severe swelling, pain, and burning sensations where injuries occur.
It is believed that the tendon can not undergo a matrix change and that the tenocytes can not be repaired. However, it has since been pointed out that, throughout one's lifetime, tenocytes in active tendons synthesizing matrix components as well as enzymes such as metalloproteinase matrices (MMPs) can derive matrices. Tendons are able to heal and recover from injury in processes controlled by the surrounding tenocytes and extracellular matrices.
The three main stages of tendon healing are inflammation, repair or proliferation, and remodeling, which can be subdivided into consolidation and maturation. These stages can overlap with each other. In the first stage, inflammatory cells such as neutrophils are recruited to the site of injury, along with erythrocytes. Monocytes and macrophages are recruited within the first 24 hours, and necrotic material phagocytosis at the site of injury occurs. After the release of vasoactive and chemotactic factors, angiogenesis and proliferation of tenocytes begin. Tenocytes then moved to the site and began to synthesize collagen III. After a few days, the repair or proliferation stage begins. At this stage, tenocytes are involved in the synthesis of large amounts of collagen and proteoglycans at the site of injury, and high levels of GAG and water. After about six weeks, the remodeling stage begins. The first part of this phase is consolidation, which lasts about six to ten weeks after the injury. During this time, the synthesis of collagen and GAG decreases, and cellularity also decreases as the tissue becomes more fibrous as a result of increased production of collagen I and fibrils being paralleled in the direction of mechanical stress. The final maturation stage occurs after ten weeks, and during this time there is an increase in crosslinked collagen fibrils, which causes the tissue to become stiff. Gradually, for about a year, the tissue will change from fibrous to like a scar.
Matrix metalloproteinases (MMPs) have a very important role in ECM degradation and remodeling during the healing process after tendon injury. Certain MMP-MMPs including MMP-1, MMP-2, MMP-8, MMP-13, and MMP-14 have collagenase activity, which means that, unlike many other enzymes, they can lower collagen I fibrils. Collagen fibril degradation by MMP-1 together with the presence of collagen denaturation is a factor believed to cause weakening of the ECM tendon and an increased potential for other ruptures to occur. In response to repeated mechanical loading or injury, cytokines may be released by the tenocytes and may cause MMP release, leading to ECM degradation and causing recurrent injuries and chronic tendinopathy.
Various other molecules are involved in tendon repair and regeneration. There are five growth factors that have been shown to be significantly regulated and active during tendon healing: growth factors such as insulin 1 (IGF-I), platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF ), and change the growth factor of beta (TGF-?). All these growth factors have different roles during the healing process. IGF-1 increases the production of collagen and proteoglycans during the first stage of inflammation, and PDGF is also present during the early stages after injury and increases the synthesis of other growth factors along with DNA synthesis and tendon cell proliferation. Three isoforms from TGF-? (TGF-1, TGF-2, TGF-3) are known to play a role in wound healing and scar formation. VEGF is notorious for promoting angiogenesis and for inducing cell proliferation and endothelial cell migration, and VEGF mRNA has been shown to be expressed at the site of tendon injury along with collagen I mRNA. Bone morphogenetic proteins (BMPs) are a subgroup of TGF-? superfamily that can induce bone formation and cartilage and tissue differentiation, and BMP-12 has been specifically shown to influence the formation and differentiation of tendon tissue and to promote fibrogenesis.
Effects of activity on healing
In animal models, extensive research has been done to investigate the effects of mechanical strain in the form of activity levels on tendon and healing injuries. While stretching may interfere with healing during the initial inflammatory phase, it has been shown that the controlled movement of the tendon after about a week after the acute injury may help to promote collagen synthesis by tenocytes, leading to increased tensile strength and diameter. the healed tendon and fewer adhesions than the immobilized tendons. In chronic tendon injury, mechanical loading has also been shown to stimulate fibroblast proliferation and collagen synthesis along with collagen restructuring, all of which promote repair and remodeling. To further support the theory that motion and activity help tendon healing, it has been shown that tendon immobilization after injury often has a negative effect on healing. In rabbits, immobilized collagen fascia has shown a decrease in tensile strength, and immobilization also results in lower water quantities, proteoglycans, and collagen crosslinking of the tendon.
Several mechanisms of mechanotransduction have been proposed as an excuse for the response of tenocytes to mechanical forces that enable them to alter the expression of their genes, protein synthesis, and cell phenotypes, and ultimately lead to changes in tendon structure. The main factor is the mechanical deformation of the extracellular matrix, which can affect the actin cytoskeleton and therefore affect cell shape, motility, and function. Mechanical strength can be transmitted by focal adhesion sites, integrins, and cell connections. Changes in actin cytoskeleton can activate integrins, which mediate the "outer-in" and "in-out" signals between cells and matrices. G-protein, which induces an intracellular signaling cascade, may also be important, and ion channels are activated by stretching to allow ions such as calcium, sodium, or potassium to enter the cell.
Society and culture
Sinew is widely used throughout the pre-industrial era as a strong and durable fiber. Some specific uses include using muscles as a thread to sew, attaching feathers to arrows (see fletch), hitting toolbars to shafts, etc. It is also recommended in survival guides as the material from which a strong rope can be made for items such as traps or living structures. Tendons should be treated in special ways to function benefically for these purposes. Inuits and other circumpolar people use muscles as the only straps for all household purposes because of the lack of other suitable sources of fiber in their ecological habitats. The elastic properties of certain veins are also used in the engineered composite arc favored by the nomadic nomads of Eurasia. The first stone to cast artillery also uses the elastic properties of the muscles.
Sin makes an excellent binder for three reasons: It is very strong, contains natural glue, and shrinks when it dries, eliminating the need for a knot.
Culinary used
Tendons (in particular, beef tendon) are used as food in some Asian dishes (often served in yum cha or dim sum restaurants). One popular dish is suan bao niu jin , in which the tendon is soaked in garlic. It is also sometimes found in Vietnamese noodle dishes ph ?.
Clinical interests
Injuries
Tendons are subject to many types of injuries. There are different forms of tendinopathies or tendon injuries due to overuse. These types of injuries generally result in inflammation and degeneration or weak tendon, which can eventually lead to tendon rupture. Tendinopathies can be caused by a number of factors related to the extracellular tendon matrix (ECM), and their classification has been difficult because their symptoms and histopathology are often similar.
The first category of tendinopathy is paratenonitis, which refers to parenteric inflammation, or paratendinous sheets that lie between the tendon and the sheath. Tendinosis refers to non-inflammatory injury to the tendon at the cellular level. This degradation is caused by damage to collagen, cells, and vascular components of the tendon, and is known to cause rupture. The observation of spontaneous ruptured tendons has shown the presence of collagen fibrils that are not in true or uniform parallel orientations in length or diameter, along with rounded tenocytes, other cell abnormalities, and blood vessel growth. Other forms of tendinosis that do not cause rupture also show degeneration, disorientation, and collagen fibril thinning, along with an increase in the amount of glycosaminoglycan between fibrils. The third is paratenonitis with tendinosis, in which a combination of parenonic inflammation and tendon degeneration are present. The latter is tendinitis, which refers to degeneration with tendon inflammation as well as vascular disorders.
Tendinopathies may be caused by several intrinsic factors including age, weight, and nutrition. Extrinsic factors are often associated with exercise and include excessive force or loading, poor training techniques, and environmental conditions.
Other animals
In some organisms, the famous birds and dinosaurs ornithischians, part of the tendon can become stiff. In this process, the osteocytes infiltrate the tendons and place the bone as in a sesamoid bone such as a patella. In birds, tendon hardening occurs mainly in hindlimb, while in ornithischian dinosaurs, rigid axial muscle tendons form a lattice along the neural and haemal spines on the tail, possibly for support.
See also
- Aponeurosis
- Cartilage
- Chordae tendineae
- List of human body muscles
- Tendon sheath
- Tendinopathy
References
Source of the article : Wikipedia
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