Functional Roles of Hyaline and Elastic Cartilage in Animals
Hyaline Cartilage: Unlike the elastic cartilage, the matrix of the hyaline cartilage consists of a translucent material called chodrin, which is mainly a mucopolysaccharide with combined sulphate groups. It is a firm, bluish-white, and somewhat elastic material; sometimes fine fibres may be present. The skeleton of the embryo mammal at one stage consists entirely of cartilage. Gradually, most of it is replaced by bone, cartilage remaining in the following locations: xisphisternal cartilage, the sterna ribs, the suprascapular cartilage and thin plates between diaphysis and epiphysis of bones, and the articular cartilages at the ends of bones. In the elasmobranch fishes, the skeleton remains cartilaginous throughout life, e.g. dogfish.
Each plate of hyaline cartilage is covered by a tough fibrous sheath, the perichodrium. The cells which secrete the chondrin, chondroblasts, lie in small spaces called lacunae, in life, they completely fill these lacunae, lying singly, or in twos, fours or eights. The fibres of cartilage are very difficult to demonstrate, and in some cases there do not appear to be any.
Fibro-Cartilage
In addition to the chondroblasts in their lacunae, the matrix is well packed with bundles of white fibres. Thus the flexibility of this tissue is combined with firmness of the fibres. Fibro-cartilage is found in the intervertebral discs, where its cushioning effect between the vertebrae is important, and in the pubic symphsis. Here it allows of parturition without complete breakage.
Elastic Cartilage
This is another variety of cartilage in which yellow fibres form an anastomosing network. The flexibility of this tissue is enhanced by the presence of these elastic fibres, and the tissue readily recovers shape after distortion. Elastic cartilage is present in the epiglottis, the external ear, and supporting the Eustachian tube and the external auditory meatus.
Bone
Bone is connective tissue with a large amount of intercellular substance consisting of mineral salts; two –thirds of the weight of a bone is mineral. The mixture of salts consists of 85 percent calcium phosphate, 10 percent calcium carbonate, about 4 percent of magnesium chloride and 1 per cent of calcium fluoride. It is very strong and rigid tissue, providing efficient levers and adequate protection for delicate organs such as the brain and spinal cord. About 15 per cent of the body weight of a an adult mammal is bone.
Each bone is enclosed in tough sheath of fibrous connective tissue, the periosteum. Underneath the periosteum is very dense layer of compact bone, beneath which is a thicker zone of cancellated or spongy bone. In the long bones, a marrow cavity is Present: this is the site of formation of most of the blood corpuscles compact bone consists of longitudinal Haversian systems. Each system comprises a central Haversian canal surrounded by successive lamellae of salts. In life, the canal contains an artery, a vein, a lymphatic vessels, a nerve and some bone cells or osteocytes. All are packed in with areolar connective tissue. At intervals among the lamellae are ostocytes lying I lacunae. From the osteocytes, fine protoplasmic connexions ramify throughout the matrix in minute canaliculi, in longitudinal section. it can be seen that the Haversian canals are connected by the transverse Volkmann’s canals.
When the cartilage in a joint becomes damaged, it causes pain and limits movement. Surgery can repair the damage. Two procedures that can help are microfracture and autologous chondrocyte implantation (ACI).
Hyaline cartilage is opaque and has a glassy appearance under a microscope. Chondrocytes are located within matrix cavities called lacunae, which appear darker than the surrounding tissue.
Functional Roles
Hyaline cartilage (which is also called articular cartilage) covers the articulating surfaces of joints to reduce friction between bones during movement. It is non-mineralized and possesses a dense extracellular matrix with long, cross-linked collagen fibers. This characteristic makes it highly refractile and resistant to mechanical loading. During skeletal development, hyaline cartilage forms the cartilaginous model of developing long bones and the epiphyseal plates attached to the ends of bones that are eventually replaced by bone as they grow out during adolescence.
Histologically, hyaline cartilage is very basophilic due to its high concentration of sulfated glycosaminoglycans and thus readily stains with hematoxylin and eosin (H&E) or picric acid/acid fuchsin (Van Geison). It also contains lacunae that can be seen under the light microscope when using either of these staining methods.
Elastic cartilage is yellow in color and consists of an elastic fiber network that gives the tissue flexibility. Chondrocytes lie within the matrix and lacunae of elastic cartilage. This cartilage is found in the external ear pinnae, larynx, eustachian tube and nose. Elastic cartilage can be distinguished from hyaline cartilage by the cellular appearance under the microscope and a lack of chondroitin sulfate. It is the least common form of cartilage.
Types of Cartilage
Hyaline cartilage is a type of connective tissue. It is found on the ends of bones in free-moving joints as articular cartilage, and it forms part of the structures in the nose, larynx, trachea, and bronchi. It is resilient and can withstand deformation by compressive forces. It does not contain blood vessels or nerves and it obtains its nutrients by diffusion from the nearby tissues. It has a glassy appearance and is bluish-white in color. It is the most common type of cartilage in the body.
The cells in hyaline cartilage are called chondrocytes and they lie in spaces (lacunae) within the extracellular matrix. The matrix is a ground substance that is made of collagen fibers and proteoglycans. The collagen fibers provide strength, and the proteoglycans give cartilage its elasticity. The extracellular matrix contains a watery fluid known as synovial fluid that helps the cartilage move more easily.
Elastic cartilage has similar microanatomy to hyaline cartilage. It has a perichondrium layer composed of fibroblasts and an inner undifferentiated chondrogenic layer. It is surrounded by two types of extracellular matrix: territorial and interterritorial. The territorial matrix is rich in a glycosaminoglycan called chondroitin sulfate. The interterritorial matrix has elastic fiber networks in addition to the collagen fibers. Like hyaline cartilage, elastic cartilage is able to flex. When a light microscopic section of elastic cartilage is stained for elastin, the matrix appears eosinophilic.
Repair of Cartilage
Research is being done to find ways to help the body grow healthy cartilage. One approach uses growth factors to stimulate the development of new cartilage tissue. Another uses mesenchymal stem cells, which are basic human cells that can develop into different types of tissue.
Hyaline cartilage lines many joints and caps the ends of bones that form joint surfaces. It is slippery and smooth, which helps bones move easily past each other in a joint. It is also strong enough to support the weight of your body. Hyaline cartilage is most likely the tissue that was damaged in your knee injury.
Elastic cartilage is yellow and springy, and can bend a lot before it breaks. This type of cartilage is found in the nose and ears. Elastic cartilage is also used in the trachea and larynx (voice box) as well as the ribs.
Under a microscope, elastic cartilage looks similar to hyaline cartilage. When it is stained with haematoxylin and eosin (H&E), elastic cartilage has a dark appearance that is sometimes difficult to distinguish from hyaline cartilage. However, elastic cartilage can be differentiated from hyaline cartilage by the presence of chondroitin sulfate.
Fibrous cartilage is the strongest type of cartilage. It has a dense structure with a layer of tough, interlocking collagen fibres. It is surrounded by a fibrous layer of perichondrium and an inner undifferentiated chondrogenic layer.
Where can cartilage be found?
Hyaline cartilage is found in structures like the nose, ears, and areas where the ribs attach to the sternum and trachea, where it provides support but also allows flexibility. Cartilage is also present on the ends of bones where it helps reduce friction in joints. This hyaline cartilage is called articular cartilage.
Under a microscope, hyaline cartilage looks similar to bone connective tissue but has a glassy appearance. The ground substance in hyaline cartilage contains proteoglycans, large molecules made of carbohydrates (repeating disaccharide units known as glycosaminoglycans or GAGs) attached to a protein core. These molecules bind together to create a gel-like fluid, which allows cartilage to resist compression.
The cells in hyaline cartilage are called chondrocytes and they produce the extracellular matrix in which they reside. Chondrocytes are arranged in small clusters inside the cartilage, called lacunae. The chondrocytes do not contact each other directly, but they interact through the cartilaginous extracellular matrix. The matrix contains a type of collagen, called type II collagen, which makes up around 40% of the cartilage’s dry weight. The matrix also contains a substance called aggrecan, which is composed of proteoglycans and hyaluronic acid.
Elastic cartilage has a yellow color and, under the microscope, it resembles hyaline cartilage but has a more solid structure. It contains networks of elastic fibers that give it its elasticity. It can withstand repeated bending and is found in the pinnae of the external ear and the epiglotis in the larynx. It is also a component of the ligaments that hold joints together.
