Tendon
Tendon | |
---|---|
Details | |
Identifiers | |
Latin | tendo |
MeSH | D013710 |
TH | H3.03.00.0.00020 |
FMA | 9721 |
Anatomical terminology |
A tendon or sinew is a tough band of
Tendons, like
Structure
A tendon is made of
Extracellular matrix
The dry mass of normal tendons, which is 30–45% of their total mass, is made of:
- 60–85% collagen
- 60–80% collagen I
- 0–10% collagen III
- 2% collagen IV
- small amounts of collagens V, VI, and others
- 15–40% non-collagenous extracellular matrix components, including:
Although most of a tendon's collagen is
Ultrastructure and collagen synthesis
Collagen fibres coalesce into
The collagen in tendons are held together with proteoglycan (a compound consisting of a protein bonded to glycosaminoglycan groups, present especially in connective tissue) components including decorin and, in compressed regions of tendon, aggrecan, which are capable of binding to the collagen fibrils at specific locations.[13] The proteoglycans are interwoven with the collagen fibrils – their glycosaminoglycan (GAG) side chains have multiple interactions with the surface of the fibrils – showing that the proteoglycans are important structurally in the interconnection of the fibrils.[14] The major GAG components of the tendon are dermatan sulfate and chondroitin sulfate, which associate with collagen and are involved in the fibril assembly process during tendon development. Dermatan sulfate is thought to be responsible for forming associations between fibrils, while chondroitin sulfate is thought to be more involved with occupying volume between the fibrils to keep them separated and help withstand deformation.[15] The dermatan sulfate side chains of decorin aggregate in solution, and this behavior can assist with the assembly of the collagen fibrils. When decorin molecules are bound to a collagen fibril, their dermatan sulfate chains may extend and associate with other dermatan sulfate chains on decorin that is bound to separate fibrils, therefore creating interfibrillar bridges and eventually causing parallel alignment of the fibrils.[16]
Tenocytes
The
Blood vessels may be visualized within the endotendon running parallel to collagen fibres, with occasional branching transverse anastomoses.
The internal tendon bulk is thought to contain no nerve fibres, but the epitenon and paratenon contain nerve endings, while
Tendon length varies in all major groups and from person to person. Tendon length is, in practice, the deciding factor regarding actual and potential muscle size. For example, all other relevant biological factors being equal, a man with a shorter tendons and a longer biceps muscle will have greater potential for muscle mass than a man with a longer tendon and a shorter muscle. Successful
Tendon length is determined by genetic predisposition, and has not been shown to either increase or decrease in response to environment, unlike muscles, which can be shortened by trauma, use imbalances and a lack of recovery and stretching.[20] In addition tendons allow muscles to be at an optimal distance from the site where they actively engage in movement, passing through regions where space is premium, like the carpal tunnel.[18]
List of Tendons
There are about 4000 tendons in the human body, of which 55 are listed here:
Name | Human body part | Function |
---|---|---|
Teres minor tendons | Shoulders and Arms | Rotator cuff tendons at the shoulder |
Infraspinatus tendons | Shoulders and Arms | Rotator cuff tendons at the shoulder |
Supraspinatus tendons | Shoulders and Arms | Rotator cuff tendons at the shoulder |
Subscapularis tendons | Shoulders and Arms | Rotator cuff tendons at the shoulder |
Deltoid tendons | Shoulders and Arms | help bend the elbow or rotate the forearm |
Biceps tendons | Shoulders and Arms | help bend the elbow or rotate the forearm |
Triceps tendons | Shoulders and Arms | help bend the elbow or rotate the forearm |
Brachioradialis tendons | Shoulders and Arms | Help bend the elbow or rotate the forearm |
Supinator tendons | Shoulders and Arms | Help bend the elbow or rotate the forearm |
Flexor carpi radialis tendons | Shoulders and Arms | help bend the wrist |
Flexor carpi ulnaris tendons | Shoulders and Arms | help bend the wrist |
Extensor carpi radialis tendons | Shoulders and Arms | help bend the wrist |
Extensor carpi radialis brevis tendons | Shoulders and Arms | help bend the wrist |
Iliopsoas tendons | Hips and Legs | bend backwards and forwards, and when you swing your leg while walking |
Obturator internus tendons | Hips and Legs | bend backwards and forwards, and when you swing your leg while walking |
Adductor longus, brevis and magnus tendons | Hips and Legs | bend backwards and forwards, and when you swing your leg while walking |
Gluteus maximus | Hips and Legs | bend backwards and forwards, and when you swing your leg while walking |
gluteus medius tendons | Hips and Legs | bend backwards and forwards, and when you swing your leg while walking |
Quadriceps tendons(patellar tendon/ patella) | Hips and Legs | bend or straighten the knee include |
Hamstring tendons | Hips and Legs | bend or straighten the knee include |
Sartorius tendons | Hips and Legs | bend or straighten the knee include |
Gastrocnemius tendons | Hips and Legs | cross the ankle joint and help move your foot up and down, or side to side |
Achilles tendon | Hips and Legs | cross the ankle joint and help move your foot up and down, or side to side |
Soleus tendons | Hips and Legs | cross the ankle joint and help move your foot up and down, or side to side |
Tibialis anterior tendons | Hips and Legs | cross the ankle joint and help move your foot up and down, or side to side |
Peroneus longus tendons | Hips and Legs | cross the ankle joint and help move your foot up and down, or side to side |
Flexor digitorum longus tendons | Hands and Feet | help you move your fingers and toes |
Interosseus tendons | Hands and Feet | help you move your fingers and toes |
Flexor digitorum profundus tendons | Hands and Feet | help you move your fingers and toes |
Abductor digiti minimi tendons | Hands and Feet | help you move your fingers and toes |
Opponens pollicis tendons | Hands and Feet | thumbs can move toward and away from your other fingers |
Flexor pollicis longus tendons | Hands and Feet | thumbs can move toward and away from your other fingers |
Extensor pollicis tendons | Hands and Feet | thumbs can move toward and away from your other fingers |
abductor pollicis tendons | Hands and Feet | thumbs can move toward and away from your other fingers |
Flexor hallucis longus tendons | Hands and Feet | bend and straighten your toes |
Flexor digitorum brevis tendons | Hands and Feet | bend and straighten your toes |
Lumbrical tendons | Hands and Feet | bend and straighten your toes |
Abductor hallucis tendons | Hands and Feet | bend and straighten your toes |
Flexor digitorum longus tendons | Hands and Feet | bend and straighten your toes |
Abductor digiti minimi tendons | Hands and Feet | bend and straighten your toes |
Ocular tendons | Head, Neck and Torso | eyes, eyelids and jaw |
Levator palpebrae tendons | Head, Neck and Torso | eyes, eyelids and jaw |
Masseter tendons | Head, Neck and Torso | eyes, eyelids and jaw |
Temporalis tendons | Head, Neck and Torso | eyes, eyelids and jaw |
Trapezius tendons | Head, Neck and Torso | move your head and neck |
Sternocleidomastoid tendons | Head, Neck and Torso | move your head and neck |
Semispinalis capitis | Head, Neck and Torso | move your head and neck |
splenius capitis tendons | Head, Neck and Torso | move your head and neck |
Mylohyoid | Head, Neck and Torso | move your head and neck |
thyrohyoid tendons | Head, Neck and Torso | move your head and neck |
Rectus abdominis tendons | Head, Neck and Torso | twist and turn your body, maintain your posture, or bend and straighten your trunk |
External oblique tendons | Head, Neck and Torso | twist and turn your body, maintain your posture, or bend and straighten your trunk |
Transversus abdominis tendons | Head, Neck and Torso | twist and turn your body, maintain your posture, or bend and straighten your trunk |
Latissimus dorsi tendons | Head, Neck and Torso | twist and turn your body, maintain your posture, or bend and straighten your trunk |
Erector spinae tendons | Head, Neck and Torso | twist and turn your body, maintain your posture, or bend and straighten your trunk |
Naming convention for the table:
Column | Explanation | Formatting |
---|---|---|
Name | the name of the Tendon in Latin | include/exclude Tendon in the name??? |
part of the human body | Where it can be found in the human body | ???? |
Function | What is its purpose in the body | ??? |
Composition | An overview of the materials that the tendon is made of | Ideally given in %? |
Functions
Traditionally, tendons have been considered to be a mechanism by which muscles connect to bone as well as muscles itself, functioning to transmit forces. This connection allows tendons to passively modulate forces during locomotion, providing additional stability with no active work. However, over the past two decades, much research has 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 some predominantly positioning limbs, such as the fingers when writing (positional tendons) and others acting as springs to make locomotion more efficient (energy storing tendons).[21] Energy storing tendons can store and recover energy at high efficiency. For example, during a human stride, the Achilles tendon stretches as the ankle joint dorsiflexes. During the last portion of the stride, as the foot plantar-flexes (pointing the toes down), the stored elastic energy is released. Furthermore, because the tendon stretches, the muscle is able to function with less or even no change in length, allowing the muscle to generate more force.
The mechanical properties of the tendon are dependent on the collagen fiber diameter and orientation. The collagen fibrils are parallel to each other and closely packed, but show a wave-like appearance due to planar undulations, or crimps, on a scale of several micrometers.[22] In tendons, the collagen fibres have some flexibility due to the absence of hydroxyproline and proline residues at specific locations in the amino acid sequence, which allows the formation of other conformations such as bends or internal loops in the triple helix and results in the development of crimps.[23] The crimps in the collagen fibrils allow the tendons to have some flexibility as well as a low compressive stiffness. In addition, because the tendon is a multi-stranded structure made up of many partially independent fibrils and fascicles, it does not behave as a single rod, and this property also contributes to its flexibility.[24]
The proteoglycan components of tendons also are important to the mechanical properties. While the collagen fibrils allow tendons to resist tensile stress, the proteoglycans allow them to resist compressive stress. These molecules are very hydrophilic, meaning that they can absorb a large amount of water and therefore have a high swelling ratio. Since they are noncovalently bound to the fibrils, they may reversibly associate and disassociate so that the bridges between fibrils can be broken and reformed. This process may be involved in allowing the fibril to elongate and decrease in diameter under tension.[25] However, the proteoglycans may also have a role in the tensile properties of tendon. The structure of tendon is effectively a fibre composite material, built as a series of hierarchical levels. At each level of the hierarchy, the collagen units are bound together by either collagen crosslinks, or the proteoglycans, to create a structure highly resistant to tensile load.[26] The elongation and the strain of the collagen fibrils alone have been shown to be much lower than the total elongation and strain of the entire tendon under the same amount of stress, demonstrating that the proteoglycan-rich matrix must also undergo deformation, and stiffening of the matrix occurs at high strain rates.[27] This deformation of the non-collagenous matrix occurs at all levels of the tendon hierarchy, and by modulating the organisation and structure of this matrix, the different mechanical properties required by different tendons can be achieved.[28] Energy storing tendons have been shown to utilise significant amounts of sliding between fascicles to enable the high strain characteristics they require, whilst positional tendons rely more heavily on sliding between collagen fibres and fibrils.[29] However, recent data suggests that energy storing tendons may also contain fascicles which are twisted, or helical, in nature - an arrangement that would be highly beneficial for providing the spring-like behaviour required in these tendons.[30]
Mechanics
Tendons are
Several studies have demonstrated that tendons respond to changes in mechanical loading with growth and remodeling processes, much like
Clinical significance
Injury
Tendons are subject to many types of injuries. There are various forms of tendinopathies or tendon injuries due to overuse. These types of injuries generally result in inflammation and degeneration or weakening of the tendons, which may eventually lead to tendon rupture.[36] Tendinopathies can be caused by a number of factors relating to the tendon extracellular matrix (ECM), and their classification has been difficult because their symptoms and histopathology often are similar.
Types of tendinopathy include:[37]
- Tendinosis: non-inflammatory injury to the tendon at the cellular level. The degradation is caused by damage to collagen, cells, and the vascular components of the tendon, and is known to lead to rupture.[38] Observations of tendons that have undergone spontaneous rupture have shown the presence of collagen fibrils that are not in the correct parallel orientation or are not uniform in length or diameter, along with rounded tenocytes, other cell abnormalities, and the ingrowth of blood vessels.[36] Other forms of tendinosis that have not led to rupture have also shown the degeneration, disorientation, and thinning of the collagen fibrils, along with an increase in the amount of glycosaminoglycans between the fibrils.[39]
- Tendinitis: degeneration with inflammation of the tendon as well as vascular disruption.[7]
- Paratenonitis: inflammation of the paratenon, or paratendinous sheet located between the tendon and its sheath.[37]
Tendinopathies may be caused by several intrinsic factors including age, body weight, and nutrition. The extrinsic factors are often related to sports and include excessive forces or loading, poor training techniques, and environmental conditions.[40]
Healing
It was believed that tendons could not undergo matrix turnover and that tenocytes were not capable of repair. However, it has since been shown that, throughout the lifetime of a person, tenocytes in the tendon actively synthesize matrix components as well as enzymes such as
The three main stages of tendon healing are inflammation, repair or proliferation, and remodeling, which can be further divided into consolidation and maturation. These stages can overlap with each other. In the first stage, inflammatory cells such as
Matrix metalloproteinases (MMPs) have a very important role in the degradation and remodeling of the ECM during the healing process after a tendon injury. Certain MMPs including MMP-1, MMP-2, MMP-8, MMP-13, and MMP-14 have collagenase activity, meaning that, unlike many other enzymes, they are capable of degrading collagen I fibrils. The degradation of the collagen fibrils by MMP-1 along with the presence of denatured collagen are factors that are believed to cause weakening of the tendon ECM and an increase in the potential for another rupture to occur.
A variety of other molecules are involved in tendon repair and regeneration. There are five growth factors that have been shown to be significantly upregulated and active during tendon healing: insulin-like growth factor 1 (IGF-I), platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and transforming growth factor beta (TGF-β).[41] These growth factors all have different roles during the healing process. IGF-1 increases collagen and proteoglycan production during the first stage of inflammation, and PDGF is also present during the early stages after injury and promotes the synthesis of other growth factors along with the synthesis of DNA and the proliferation of tendon cells.[41] The three isoforms of TGF-β (TGF-β1, TGF-β2, TGF-β3) are known to play a role in wound healing and scar formation.[43] VEGF is well known to promote angiogenesis and to induce endothelial cell proliferation and migration, and VEGF mRNA has been shown to be expressed at the site of tendon injuries along with collagen I mRNA.[44] Bone morphogenetic proteins (BMPs) are a subgroup of TGF-β superfamily that can induce bone and cartilage formation as well as tissue differentiation, and BMP-12 specifically has been shown to influence formation and differentiation of tendon tissue and to promote fibrogenesis.
Effects of activity on healing
In animal models, extensive studies have been conducted to investigate the effects of mechanical strain in the form of activity level on tendon injury and healing. While stretching can disrupt healing during the initial inflammatory phase, it has been shown that controlled movement of the tendons after about one week following an acute injury can help to promote the synthesis of collagen by the tenocytes, leading to increased tensile strength and diameter of the healed tendons and fewer adhesions than tendons that are immobilized. In chronic tendon injuries, mechanical loading has also been shown to stimulate fibroblast proliferation and collagen synthesis along with collagen realignment, all of which promote repair and remodeling.[41] To further support the theory that movement and activity assist in tendon healing, it has been shown that immobilization of the tendons after injury often has a negative effect on healing. In rabbits, collagen fascicles that are immobilized have shown decreased tensile strength, and immobilization also results in lower amounts of water, proteoglycans, and collagen crosslinks in the tendons.[36]
Several
Society and culture
Sinew was widely used throughout
Sinew makes for an excellent cordage material for three reasons: It is extremely strong, it contains natural glues, and it shrinks as it dries, doing away with the need for knots[clarification needed].
Culinary uses
Tendon (in particular,
Other animals
In some organisms, notably birds,[45] and ornithischian dinosaurs,[46] portions of the tendon can become ossified. In this process, osteocytes infiltrate the tendon and lay down bone as they would in sesamoid bone such as the patella. In birds, tendon ossification primarily occurs in the hindlimb, while in ornithischian dinosaurs, ossified axial muscle tendons form a latticework along the neural and haemal spines on the tail, presumably for support.
See also
- Aponeurosis
- Cartilage
- Chordae tendineae
- List of muscles of the human body
- Tendon sheath
References
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- ^ "Framing Within Our Bodies". Southern Hills Hospital & Medical Center. Retrieved 2023-09-11.
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- ^ Dorlands Medical Dictionary 2012.Page 1382
- ^ a b c Jozsa, L., and Kannus, P., Human Tendons: Anatomy, Physiology, and Pathology. Human Kinetics: Champaign, IL, 1997.
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- ^ a b Benjamin, M., Tendons and ligaments - an overview (PDF), vol. 1, p. 10
- ^ "Having a short Achilles tendon may be an athlete's Achilles heel". Archived from the original on 2007-10-21. Retrieved 2007-10-26.
- ^ Young, Michael. "A Review on Postural Realignment and its Muscular and Neural Components" (PDF). Archived from the original (PDF) on 2019-04-06. Retrieved 2010-06-23.
- ^ Thorpe C.T., Birch H.L., Clegg P.D., Screen H.R.C. (2013). The role of the non-collagenous matrix in tendon function. Int J ExpPathol. 94;4: 248-59.
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