Cartilage ˈ is a flexible connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...

 found in many areas in the bodies of humans and other animals, including the joints between bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

s, the rib cage
Rib cage
The rib cage is an arrangement of bones in the thorax of animals. It is formed by the vertebral column, ribs and sternum and encloses the heart and lungs....

, the ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....

, the nose
Anatomically, a nose is a protuberance in vertebrates that houses the nostrils, or nares, which admit and expel air for respiration in conjunction with the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passes through the pharynx, shared with the...

, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral disc
Intervertebral disc
Intervertebral discs lie between adjacent vertebrae in the spine. Each disc forms a cartilaginous joint to allow slight movement of the vertebrae, and acts as a ligament to hold the vertebrae together.-Structure:...

s. It is not as hard and rigid as bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

 but is stiffer and less flexible than muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...


Cartilage is composed of specialized cells called chondroblast
A chondroblast is a cell which originates from a mesenchymal stem cell and forms chondrocytes, commonly known as cartilage cells. Chondroblasts that become embedded in the matrix are called chondrocytes. They lie in the space or lacunae present in the groups of two or more. The groups are formed by...

s that produce a large amount of extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...

 composed of Type II collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...

 (except fibrocartilage which also contains type I collagen) fibers, abundant ground substance
Ground substance
Ground substance is a term for the non-cellular components of extracellular matrix which contain the fibers.It is usually not visible on slides, because it is removed during the preparation process....

 rich in proteoglycan
Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan chain. The point of attachment is a Ser residue to which the glycosaminoglycan is joined through a tetrasaccharide bridge...

, and elastin
Elastin is a protein in connective tissue that is elastic and allows many tissues in the body to resume their shape after stretching or contracting. Elastin helps skin to return to its original position when it is poked or pinched. Elastin is also an important load-bearing tissue in the bodies of...

 fibers. Chondroblasts that get caught in the matrix are called chondrocyte
Chondrocytes are the only cells found in cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans...

s. They lie in spaces, called lacunae, with up to eight chondrocytes per lacuna. Cartilage is classified in three types, elastic cartilage
Elastic cartilage
Elastic cartilage or yellow cartilage is a type of cartilage present in the outer ear, larynx, and epiglottis. It contains elastic fiber networks and collagen fibers. The principal protein is elastin....

, hyaline cartilage
Hyaline cartilage
Hyaline cartilage consists of a slimy mass, pearly bluish in colour with firm consistency and considerable collagen. It contains no nerves or blood vessels, and its structure is relatively simple....

and fibrocartilage
White fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. It owes its flexibility and toughness to the former of these constituents, and its elasticity to the latter...

, which differ in the relative amounts of these three main components.

Unlike other connective tissues, cartilage does not contain blood vessels. Because of this, it heals very slowly. The chondrocytes are supplied by diffusion, helped by the pumping action generated by compression of the articular cartilage or flexion of the elastic cartilage. Thus, compared to other connective tissues, cartilage grows and repairs more slowly.

Growth and development

In embryogenesis
Embryogenesis is the process by which the embryo is formed and develops, until it develops into a fetus.Embryogenesis starts with the fertilization of the ovum by sperm. The fertilized ovum is referred to as a zygote...

, the skeletal system is derived from the mesoderm germ layer. Chondrification (also known as chondrogenesis) is the process by which cartilage is formed from condensed mesenchyme
Mesenchyme, or mesenchymal connective tissue, is a type of undifferentiated loose connective tissue that is derived mostly from mesoderm, although some are derived from other germ layers; e.g. some mesenchyme is derived from neural crest cells and thus originates from the ectoderm...

 tissue, which differentiates into chondroblasts and begins secreting the molecules that form the extracellular matrix.


Cartilage does not absorb x-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

s under normal In vivo
In vivo
In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...

 conditions, but a dye can be injected into the synovial membrane so the x-rays will be absorbed by the dye. The resulting void on the radiographic film between the bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

 and meniscus
Meniscus (anatomy)
In anatomy, a meniscus is a crescent-shaped fibrocartilaginous structure that, in contrast to articular disks, only partly divides a joint cavity. In humans it is present in the knee, acromioclavicular, sternoclavicular, and temporomandibular joints; in other organisms they may be present in other...

 represents the cartilage. For In vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

 scans the outer soft tissue is most likely removed so the cartilage and air boundary is enough to contrast the presence of cartilage due to refraction
Refraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...

 of the x-ray.


Why has imaging of cartilage such a high clinical value and should be optimized? Accurately described by Link et al.: “Cartilage is one of the most important biomarkers in degenerative and traumatic joint disease. MR imaging has been established as the standard cartilage imaging modality, and techniques have been developed and optimized to visualize cartilage morphology, to quantify its volume and to analyze its biochemical composition. The substantial amount of research that is invested in the development of these morphologic and quantitative imaging techniques is motivated by new therapeutic modalities both on a surgical (cartilage repair) and a pharmacological level.”
Recital of clinical indications for MRI in order to assess the cartilages actual condition: Osteoarthritis, chronic or acute osteo-chondral injury, osteochondritis dissecans, chondromalacia patellae, spontaneous osteo-necrosis of the femoral condyle (SONC or Ahlbaecks disease) and inflammatory arthropathies, evaluation of invasive surgery or monitoring of pharmacological therapies.
The higher the field strength, the higher the diagnostic value of the image. With 3.0 Tesla systems the image gains on quality and spatial resolution. The signal-to-noise ratio (SNR) correlates linearly to the field strength and is thus double compared to a 1.5 Tesla system. Additionally the contrast increases while the expenditure of time and the appearance of artifacts decrease. Those enhanced performances are of high value and importance, especially for cartilage at smaller joints. The other side of the coin is an exacerbated difference of magnetic susceptibility in-between different tissues, a higher vulnerability to flow artifacts and safety concerns.
In addition, doubling of the field strength comes along with doubling of the chemical shift. Imaging parameters must therefore be adjusted to the higher field strength, the increasing bandwidth and TR and to the decreasing flip angle and TE.

Naked-eye estimations of cartilage on MR arthrography seem to have the trend that thin regions get over- and thick regions get under-estimated. Hodler et al. noted that fact examining the humeral head, and Yeh et al. described it similarly, again concerning the humeral head. On the contrary, that trend was not found at the glenoid fossa, rather both thick and and thin regions were overestimated.

Magnetization transfer in MRI:

Wet and fatty molecules are relatively small and feature in vivo conditions of high mobility. Macromolecular protons, for example proteins, have a wider range of Larmor frequencies ( than protons of free water. Therefore can they be stimulated by radio frequency pulses. This leads to a saturated magnetization of the macromolecular protons, consequently to a decreased signal. This signal decay, called magnetization transfer, depends on the concentration of macromolecules and on interaction with free water. The decrease of signal intensity caused by magnetization transfer is in solid tissues distinct compared to the signal loss in wet and fatty tissues.
MTC magnetization transfer contrast: The indirect effects of exchange of the magnetization saturation can be measured between the free and the bound protons. This technique is applied in cartilage imaging to improve the contrast between synovial fluid and cartilage. Thanks to the fact that synovial fluid has little amount of bound protons and cartilage has a large amount, it results in a pronounced magnetization transfer.

Damage of the cartilage starts whether on the surface as superficial fissures or deeper at the collagen structures. Second leads to a disadvantageous hyperhydratation with thickening and softening.

MR system of classification after Yulish et al. based on the arthroscopic classification of Outerbridge:
  • Grade 1: Thickening and softening without morphological damage.
  • Grade 2: Including superficial fissures or fibrillation of the surface, or plane ulceration or erosion less than half way through the cartilage.
  • Grade 3: Plane ulceration or erosion partly more than half way through the cartilage, but still not throughout.
  • Grade 4: Lesion throughout the cartilage extending to the bone.

The following sequences have shown high sensitivity for detecting lesions from grade 2 to grade 4: Proton-densed and T2-weighted FSE with or without fat-suppression, T1-weighted, 3D spoiled gradient-echo (GRE) and the 3D double echo steady state (3D-DESS).

In both proton-densed and T2-weighted FSE, regardless of the fat-suppression, the detection of chondral anomalies showed a high sensitivity (>73%) and specificity (>79%). In those sequences the joint cartilage showed a lower signal intensity than the adjoining liquid. Furthermore is the cartilaginous border also without any liquid well discriminable. Those sequences have the advantages of reaching a high resolution in a short amount of time (4-5 minutes) and allow a simultaneous evaluation of other adjacent structures like tendons, ligaments or menisci.

An optimal MR pulse sequence for evaluation of cartilage should be able to:
  • Detect changes at the subchondral bone plate and their exact thickness without magnetic susceptibility.
  • Detect bone marrow edema, subchondral cysts, granulation tissue.
  • Detect internal structural changes: disruption of the collagen framework; detect changes of the biochemical composition: cutback of proteoglycans and increase of water content.
  • Clear contrast between normal and pathological cartilage irrespective of their depth.
  • Display cartilage with an optimal contrast resolution, high spatial resolution and/or allow segmentation, volume calculation and three-dimensional (3D) displaying.

During daily clinical routine are proton-densed and T2-weighted FSE images sufficient. Without fat-suppression the soft tissues like menisci, tendons and ligaments are well displayed. Fat-suppressed FSE images conduce to detect bone marrow edema. If the FSE image can’t display clearly the deepest cartilage layers, the lesion gets easily overestimated concerning its depth. Those cases require subsequently a more time-consuming high-resolution 3D sequence. Verstraete et al. recommend in order to verify a grade 2 lesion a fat-suppressed FSE sequence, since it has a similar sensibility compared to the 3D sequences and a higher one than without fat-suppression.

The cartilage imaging will particularly benefit from higher fields. The high signal-to-noise ratio in combination with dedicated coils allows morphological high resolution images. With special surface or circular coils even thin cartilage, for example at finger joints, are well presentable. The examinations take longer, but thanks to recent technologies like parallel imaging, which allows sequence acceleration, the expansion of time per case can be limited. While parallel imaging in the standard 1.5 Tesla MRI includes a loss of signal-to-noise, the high field is able to compensate the decreased ratio. The cartilage imaging via high field system also benefits from the development of so called isotropic 3D gradient echo and 3D fast spin echo techniques, which are characterized by a high contrast to noise ratio of cartilage compared to the environment around it. Isotropic describes the fact that the voxels in all directions of space have the same dimension and thus allow processing possibilities such as reformatting in every level without any loss of resolution or highly reliable segmentation for 3D visualization and volume determination of the cartilage.

It is obvious that these kind of images have a great value for preoperative clarification before cartilage cell transplantation. In addition are hence through volumetric measurements quantitative follow-ups of arthritis patients possible. For a clinical use are the stronger 3 Tesla systems recommended, given that they are superior concerning the signal-noise-ratio, the expenditure of time and thus are less vulnerable for motion artifacts. High field MRI systems have the ability for in vivo biochemical analysis of cartilage which allows early diagnosis of damage in morphologically seeming intact cartilage. Various tissue parameters that can be evaluated by MRI experiments reflect the cartilage’s biomechanical properties. Among them, the relaxation times of water are at the very fore. Quantification of T2 values lead to valuation of the water content, concentration and architecture of collagen at the extracellular matrix. Through contrast agent amplified T1 values can depict the proteoglycane concentration and arrangement in the cartilage.

Wiener E. et al. investigated the contrast agent dynamics in hyaline and fibrous cartilage of the gleno-humeral joint of cadaveric specimen after intraarticular injection of gadopentate dimeglumine and found a significant decrease in T1 already 15 minutes after injection. It accredits that dGEMRIC (delayed gadolinium enhanced MRI of cartilage) in combination with direct MR arthrography is an excellent approach for generating late enhancement images of articular cartilage. Whereupon contrast accumulation was faster in hyaline than in fibrous cartilage. To avoid false positive diagnoses it is important to know that even in intact cartilage the macromolecular concentration of glycosaminoglycane and collagen is inhomogeneous, which can affect the temporal distribution of T1 (Gd). After 2.5 hours, contrast accumulation showed a higher rate of decrease in hyaline cartilage, but neither hyaline nor fibrous cartilage had reached the equilibrium. The application of the dGEMRIC results is limited and cannot easily be extended to living subjects, since the group was small and kinetics of the contrast agent would be different.

Diseases and treatment

There are several diseases which can affect the cartilage. Chondrodystrophies are a group of diseases characterized by disturbance of growth and subsequent ossification
Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...

 of cartilage. Some common diseases affecting/involving the cartilage are listed below.
  • Osteoarthritis
    Osteoarthritis also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion...

    : The cartilage covering bones (articular cartilage - a subset of hyaline cartilage) is thinned, eventually completely worn out, resulting in a "bone against bone" joint, reduced motion, and pain. Osteoarthritis affects the joints exposed to high stress and is therefore considered the result of "wear and tear" rather than a true disease. It is treated by Arthroplasty
    Arthroplasty is an operative procedure of orthopedic surgery performed, in which the arthritic or dysfunctional joint surface is replaced with something better or by remodeling or realigning the joint by osteotomy or some other procedure.-Background:Previously, a popular form of arthroplasty was...

    , the replacement of the joint by a synthetic joint often made of a Stainless Steel alloy (cobalt chromoly) and Ultra High Molecular Weight Polyethylene (UHMWPE). Chondroitin sulfate
    Chondroitin sulfate
    Chondroitin sulfate is a sulfated glycosaminoglycan composed of a chain of alternating sugars . It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have over 100 individual sugars, each of which can be sulfated in variable positions and quantities...

    , a monomer of the polysaccharide portion of proteoglycan
    Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan chain. The point of attachment is a Ser residue to which the glycosaminoglycan is joined through a tetrasaccharide bridge...

    , has been claimed to reduce the symptoms of osteoarthritis, possibly by increasing the synthesis of the extracellular matrix, but recent research has not produced evidence to support this claim
  • Traumatic rupture or detachment: The cartilage in the knee
    The knee joint joins the thigh with the leg and consists of two articulations: one between the fibula and tibia, and one between the femur and patella. It is the largest joint in the human body and is very complicated. The knee is a mobile trocho-ginglymus , which permits flexion and extension as...

     is frequently damaged, and can be partially repaired through knee cartilage replacement therapy
    Knee cartilage replacement therapy
    Articular cartilage, most notably that which is found in the knee joint, is generally characterized by very low friction, high wear resistance, and poor regenerative qualities. It is responsible for much of the compressive resistance and load bearing qualities of the knee joint and, without it,...

  • Achondroplasia
    Achondroplasia dwarfism occurs as a sporadic mutation in approximately 85% of cases or may be inherited in an autosomal dominant genetic disorder that is a common cause of dwarfism...

    : Reduced proliferation of chondrocytes in the epiphyseal plate of long bones during infancy and childhood, resulting in dwarfism
    Dwarfism is short stature resulting from a medical condition. It is sometimes defined as an adult height of less than 4 feet 10 inches  , although this definition is problematic because short stature in itself is not a disorder....

  • Costochondritis
    Costochondritis is a benign inflammation of the costal cartilage, which is a length of cartilage which connects each rib, except the eleventh and twelfth, to the sternum. It causes pain in the chest that can be reproduced by pressing on the affected area between the ribs. This pain can be quite...

    : Inflammation of cartilage in the ribs, causing chest pain
    Chest pain
    Chest pain may be a symptom of a number of serious conditions and is generally considered a medical emergency. Even though it may be determined that the pain is non-cardiac in origin, this is often a diagnosis of exclusion made after ruling out more serious causes of the pain.-Differential...

  • Spinal disc herniation
    Spinal disc herniation
    A spinal disc herniation , informally and misleadingly called a "slipped disc", is a medical condition affecting the spine due to trauma, lifting injuries, or idiopathic, in which a tear in the outer, fibrous ring of an intervertebral disc allows the soft, central portion A spinal disc herniation...

     : Asymmetrical compression of an intervertebral disc
    Intervertebral disc
    Intervertebral discs lie between adjacent vertebrae in the spine. Each disc forms a cartilaginous joint to allow slight movement of the vertebrae, and acts as a ligament to hold the vertebrae together.-Structure:...

     ruptures the sac-like disc, causing a hernia
    A hernia is the protrusion of an organ or the fascia of an organ through the wall of the cavity that normally contains it. A hiatal hernia occurs when the stomach protrudes into the mediastinum through the esophageal opening in the diaphragm....

    tion of its soft content. The hernia often compresses the adjacent nerves and causes back pain.
  • Relapsing polychondritis: a destruction, probably autoimmune
    Autoimmunity is the failure of an organism to recognize its own constituent parts as self, which allows an immune response against its own cells and tissues. Any disease that results from such an aberrant immune response is termed an autoimmune disease...

    , of cartilage, especially of the nose and ears, causing disfiguration. Death occurs by suffocation
    Suffocation is the process of Asphyxia.Suffocation may also refer to:* Suffocation , an American death metal band* "Suffocation", a song on Morbid Angel's debut album, Altars of Madness...

     as the larynx loses its rigidity and collapses.

A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...

s made up of cartilage tissue, either benign or malignant
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

, can occur. They usually appear in bone, rarely in pre-existing cartilage. The benign tumors are called chondroma
A chondroma is a benign cartilaginous tumor, which is encapsulated with a lobular growing pattern.Tumor cells resemble normal cells and produce the cartilaginous matrix ....

, the malignant ones chondrosarcoma
Chondrosarcoma is a cancer composed of cells derived from transformed cells that produce cartilage. Chondrosarcoma is a member of a category of "soft tissue" malignancies known as sarcomas. About 30% of skeletal system cancers are chondrosarcomas...

. Tumors arising from other tissues may also produce a cartilage-like matrix, the best known being pleomorphic adenoma
Pleomorphic adenoma
Pleomorphic adenoma is a common benign salivary gland neoplasm characterised by neoplastic proliferation of parenchymatous glandular cells along with myoepithelial components, having a malignant potentiality. It is the most common type of salivary gland tumor and the most common tumor of the...

 of the salivary glands. Conversely, chondrostatin, an ingredient of cartilage, is being investigated by Washington University
Washington University School of Medicine
Washington University School of Medicine , located in St. Louis, Missouri, is one of the graduate schools of Washington University in St. Louis. One of the top medical schools in the United States, it is currently ranked 4th for research according to U.S. News and World Report and has been listed...

 researchers for its potential ability to shrink breast and musculoskeletal tumors.

The matrix of cartilage acts as a barrier, preventing the entry of lymphocytes or diffusion of immunoglobulins. This property allows for the transplantation
Organ transplant
Organ transplantation is the moving of an organ from one body to another or from a donor site on the patient's own body, for the purpose of replacing the recipient's damaged or absent organ. The emerging field of regenerative medicine is allowing scientists and engineers to create organs to be...

 of cartilage from one individual to another without fear of tissue rejection.


Cartilage has limited repair capabilities: Because chondrocytes are bound in lacunae
Lacuna (histology)
In histology, a lacuna is a small space containing an osteocyte in bone or chondrocyte in cartilage.-Bone:The Lacuna are situated between the lamella, and consist of a number of oblong spaces. In an ordinary microscopic section, viewed by transmitted light, they appear as fusiform opaque spots...

, they cannot migrate to damaged areas. Therefore if damaged
Articular cartilage damage
Cartilage structures and functions can be damaged. Such damage can result from a variety of causes, such as a bad fall or traumatic sport-accident, previous knee injuries or wear and tear over time...

, it is difficult to heal. Also, because hyaline cartilage does not have a blood supply, the deposition of new matrix is slow. Damaged hyaline cartilage is usually replaced by fibrocartilage scar tissue. Over the last years, surgeons and scientists have elaborated a series of cartilage repair procedures
Articular cartilage repair
The aim of an articular cartilage repair treatment is to restore the surface of an articular joint's hyaline cartilage. Over the last decades, surgeons and researchers have been working hard to elaborate surgical cartilage repair interventions...

 that help to postpone the need for joint replacement.

Bioengineering techniques are being developed to generate new cartilage, using a cellular "scaffolding" material and cultured cells
Autologous chondrocyte implantation
Autologous chondrocyte implantation is a biomedical treatment that repairs damages in articular cartilage. ACI provides pain relief while at the same time slowing down the progression or considerably delaying partial or total joint replacement surgery...

 to grow artificial cartilage.

Cartilaginous fish

Cartilaginous fish (chondrichthyes)
Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone...

 like shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

s, ray
Batoidea is a superorder of cartilaginous fish commonly known as rays and skates, containing more than 500 described species in thirteen families...

s and skate
Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays. There are more than 200 described species in 27 genera. There are two subfamilies, Rajinae and Arhynchobatinae ....

s have a skeleton composed entirely of cartilage. Shark cartilage
Shark cartilage
Shark cartilage is a dietary supplement made from the dried and powdered cartilage of a shark; that is, from the tough material that composes a shark's skeleton. Shark cartilage is claimed to combat and/or prevent a variety of illnesses, most notably cancer. It is often marketed under the names...

 is a popular but unproven dietary supplement.

Invertebrate cartilage

Cartilage tissue can also be found among invertebrates such as horseshoe crab
Horseshoe crab
The Atlantic horseshoe crab, Limulus polyphemus, is a marine chelicerate arthropod. Despite its name, it is more closely related to spiders, ticks, and scorpions than to crabs. Horseshoe crabs are most commonly found in the Gulf of Mexico and along the northern Atlantic coast of North America...

s, marine snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...

s, and cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...


External links

  •, International Cartilage Repair Society
  •, Cartilage tutorial, University of Kansas Medical Center
  •, text from Gray's anatomy
  •, I've heard 'Ears and nose do not ever stop growing.' Is this false?
  •, Information on Articular Cartilage Injury Prevention, Repair and Rehabilitation
  •, Osteoarthritis
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.