CLINICALCONNECTION Genetic Collagen Diseases Connective tissue, such as cartilag
ID: 194180 • Letter: C
Question
CLINICALCONNECTION Genetic Collagen Diseases Connective tissue, such as cartilage and bone, consists of cells calcium phosphate forms extensive white crystals that account embedded in a matrix containing proteins (mainly collagen) and for up to 50% of the mass of bone. By itself, calcium phos- a space-filling "ground substance" (mostly polysaccharides; see phate is brittle. Yet bone is thousands of times stronger than Section 11-3). The polysaccharides, which are highly hydrated, the crystals because it is a composite structure in which the are resilient and return to their original shape after being com- mineral is interspersed with collagen fibers. This layered pressed. The collagen fibers are strong and relatively rigid, resist arrangement dissipates stresses so that the bone remains ing tensile (stretching) forces. Together, the polysaccharides and strong but can "give" a little under pressure without shatter- collagen give ligaments (which attach bone to bone) and tendons ing. Bone tissue also includes passageways for small blood vessels. (which join muscles to bones) the appropriate degree of resistance and flexibility. The connective tissues that surround muscles and organs contain collagen fibers arranged in sheetlike networks with similar physical properties. During development, most of the skeleton takes shape as cartilaginous tissue becomes mineralized, forming hard bone. The repair of a fractured bone follows a similar process in which fibroblasts moving to the injured site synthesize large amounts of collagen, chondroblasts produce cartilage, and osteoblasts gradually replace the cartilage with bony tissue. Mature bone continues to undergo remodeling, which begins with the release of enzymes and acid from cells known as osteoclasts. The enzymes digest collagen and other extracellular matrix compo- the low pH helps dissolve calcium phosphate. Osteoblasts then fill the void with new bone material. Some bones are remodeled faster than others, and the system responds to physical demands so that the bone becomes stronger and thicker when subjected to heavy loads. This is the basis for orthodontics: Teeth are realigned by placing stress on the bone in the tooth sockets for a period long enough for remodeling to take place. The reqular arrays of collagen fibers (horizontal bands) in tendon allow the tissue to resist tension. Fibroblasts, collaqen-producinq cells, occupy the spaces between the fibers. Cartilaqe typically lacks blood vessels. [Mark Nielsen.] The importance of collagen for the structure and function of connective tissues means that irregularities in the collagen protein itself or in the enzymes that process collagen molecules can lead to serious physical abnormalities. Hundreds of colla- gen-related mutations have been identified. Because most tissues contain more than one type of collagen, the physiologi- In bone, the extracellular matrix is supplemented by min- erals, mainly hydroxyapatite, Ca(PO4h(OH). This form of cal manifestations of collagen mutations are highly variable.Explanation / Answer
During the repair of a broken bone,fibroblasts move to the injured site to produce collagen,chondroblasts produce cartilage which is replaced by bony tissue.In the next stage of remodelling,osteoclasts produce acids and enzymes which digest collagen and other extracellular matrix.Osteoblasts then fill the void with new bone material.Somes bones respond to physical demand,so that they become stronger and thicker when subjected to heavy loads.Thus the process of remodelling is faster.
Ligaments,being made up of collagen and polysaccharides,are softer than bone.Polysaccharides are resilient,return to their shape after being compressed.Collagens are also resistant to tensile forces.If a ligament is torn,then it takes longer time for the proteins to process collagens and assemble the chains of collagen fibres.And the response to physical demand is also indirect here.