GAGs are essentially long polysaccharides made of amino sugars that attract sodium and potassium ions. These ions bring water along with it. Therefore, this helps to regulate the amount of water in the extracellular matrix.
Chondroitin sulfate and keratan sulfate are examples of sulfated GAGs and hyaluronic acid is an example of no non-sulfated GAG. These are all found in the extracellular fluid of cartilage. Proteoglycans and glycoproteins are amino acids and carbohydrate molecules joined.
They bind extracellular molecules and components together giving a gel-like fluid helping to absorb compression and force. What are chondrocytes? Chondrocytes are the only cartilage cells to be found in hyaline cartilage. These cells start as chondroblasts or perichondrial cells which produce the cartilaginous matrix, then get immobilized within it in small spaces called lacunae.
The role of chondrocytes is to develop, repair, and maintain the extracellular matrix. Chondrocytes have a limited healing capacity due to their limited replication ability. They rarely form cell-cell contact and are simply responsible for maintaining their immediate surroundings. Figure 3 shows the basic structure of a chondrocyte. The hyaline cartilage is generally covered by the perichondrium. The perichondrium is found in developing bones but does not cover the articular cartilage on the ends of bones in adults.
The perichondrium consists of an outer layer and an inner layer. The outer layer is fibrous cartilage and produces collagen fibers and the inner layer is involved in the formation of cartilage by forming chondroblasts or chondrocytes. Articular cartilage is a type of hyaline cartilage. It is different from usual hyaline cartilage as it has flattened chondrocytes near the surface. In humans, it is 2 to 4 mm thick.
It does not have blood vessels, nerves, or lymphatics. Its ECM is dense whereas chondrocytes are sparse. Deeper in the tissue, the chondrocytes take a more typical structure. In the very deep layers of the cartilage, the cells are found in columns with a calcified matrix. The collagen fibers form arches giving it a strong structural arrangement to withstand pressure. Figure 4 shows the location of the articular hyaline cartilage in a joint. Articular cartilage is made up of different zones.
These include the superficial zone, followed by the middle transitional zone, the deep zone, and finally the calcified zone. Within each zone, there are 3 regions. These are the pericellular region, the territorial region, and the interterritorial region.
The video below presents the layers found in articular cartilage. Collagen fibers II and IX can be found here. It contains a large volume of chondrocytes that have a more flattened appearance. The superficial zone is in direct contact with the synovial fluid and protects the deeper layers from force and stresses.
The middle zone follows directly from the superficial zone and provides the bridge to the deeper layers. It consists of thicker collagen fibers and proteoglycans. The chondrocytes here are spherical and found in small amounts. The middles zone functions to protect against compacting forces. The deep zone follows on from the middles zone and provides the best resistance to compacting forces.
It contains the highest proteoglycan content and the least water content. The collagen fibers are arranged at right angles to the surface and the chondrocytes are arranged in columns. Finally, the calcified zone attaches the cartilage to the bone. It does this by anchoring the collagen fibers in the deep zone to the subchondral bone. As mentioned above, hyaline cartilage connective tissue is made up of cells and fibers within an extracellular matrix. Hyaline cartilage histology describes how hyaline cartilage looks when viewed under a microscope.
The chondrocytes can be seen as rounded or angular in form. In adult cartilage, the cells are present in isogenous groups, formed from a single progenitor cell. The matrix is visually homogenous and basophilic in appearance. The reason for this is because of the high concentration of sulfated GAGs in the matrix mask the collagen fibers.
Type II collagen fibers are also very small which is why the extracellular matrix appears so shiny and smooth. There is no uniform distribution within the extracellular matrix. Therefore, the three basic zones can be seen. Figure 5. Shows these different zones. The Van Geison stain uses picric acid and acid fuchsin and stains collagen red.
The cartilage is viewed as a red zone lying below the epithelium. The staining is lighter where it becomes closer to the lacunae indicating the territorial matrix. The territorial matrix is dark, and the interterritorial matrix is a lot lighter in color. These chondrocytes are derived from the same progenitor and are therefore an isogenous group. The perichondrium surrounds the cartilage except in the articular cartilage.
There are 3 different cartilage types found in the body. Hyaline cartilage is the most common but also the weakest type of cartilage. The other two types of cartilage are fibrocartilage and elastic cartilage. How is hyaline cartilage different from elastic cartilage or fibrocartilage? See below to see descriptions of each cartilage type. The visual differences between the types of cartilage can be seen in Figure 1.
Let us look at Hyaline cartilage vs elastic cartilage. White fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions.
It owes its flexibility and toughness to the fibrous tissue, and its elasticity to the cartilaginous tissue. It is the only type of cartilage that contains type I collagen in addition to the normal type II.
Fibrocartilage is found in the pubic symphysis, the annulus fibrosus of intervertebral discs, menisci, and the temporal mandibular joint. Elastic or yellow cartilage contains elastic fiber networks and collagen fibers. The principal protein is elastin. Elastic cartilage is histologically similar to hyaline cartilage but contains many yellow elastic fibers lying in a solid matrix. These fibers form bundles that appear dark under a microscope. They give elastic cartilage great flexibility so it can withstand repeated bending.
Chondrocytes lie between the fibers. Elastic cartilage is found in the epiglottis part of the larynx and the pinnae the external ear flaps of many mammals, including humans.
Key Takeaways. Key Points Cartilage is a flexible connective tissue that differs from bone in several ways; it is avascular and its microarchitecture is less organized than bone. Cartilage is not innervated and therefore relies on diffusion to obtain nutrients.
This causes it to heal very slowly. The main cell types in cartilage are chondrocytes, the ground substance is chondroitin sulfate, and the fibrous sheath is called perichondrium. There are three types of cartilage: hyaline, fibrous, and elastic cartilage. Hyaline cartilage is the most widespread type and resembles glass. Elastic cartilage provides strength, and elasticity, and maintains the shape of certain structure such as the external ear. It has a perichondrium.
Cartilage: The three types of cartilage There are three types of cartilage: Hyaline - most common, found in the ribs, nose, larynx, trachea. Is a precursor of bone. Fibro - is found in invertebral discs, joint capsules, ligaments. Elastic - is found in the external ear, epiglottis and larynx. Hyaline cartilage This is a diagram of hyaline cartilage, showing active chondrocytes sitting in their lacunae. Elastic cartilage.
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