MS path word list 1.pdf

Musculosksletal Pathology Word List PP 1 bone Four types of connec9ve 9ssue § Fibroblast, chondroblast, osteoblast, myoblast o fibrous connec7ve 7ssue o car7lage o bone Bone structure (5 func9ons) 1. Mechanical support: provide the rigid framework for the trunk and extremi7es to withstand mechanical...

Musculosksletal Pathology Word List PP 1 bone Four types of connec9ve 9ssue § Fibroblast, chondroblast, osteoblast, myoblast o fibrous connec7ve 7ssue o car7lage o bone Bone structure (5 func9ons) 1. Mechanical support: provide the rigid framework for the trunk and extremi7es to withstand mechanical loading 2. Transmission of forces generated by muscle: serve as levers for the locomotor for skeletal muscles (bones do nothing on their own) 3. Protec9on of vulnerable viscera (skull for brain) 4. Blood cell produc9on: contains hemopoie7c 7ssue (stem cells) for produc7on of erythrocytes, granular leukocytes, and platelets 5. Mineral homeostasis: organ of storage or reservoir for calcium, phosphorus, magnesium, and sodium, helping to maintain the ionized mineral homeostasis by storing or releasing these substances as the need arises – serum level dictates Osteoblast § Located at surface of ECM; mesenchymal origin § synthesize, transport, and assemble bone matrix + regulate its mineraliza7on § or synthesize & deposit osteoid Osteoclast § located at surface of bone; (NOT mesenchymal origin*) § Specialized mul9nucleated macrophages from circula7ng monocytes § ANach to ECM via surface integrins/adhesion à form resorp7on pit à secrete acid and proteases into pit à bone resorp7on (minerals return to blood for metabolic needs) Osteocyte § Located within bone, Mesenchymal origin § Interconnected by network of cytoplasmic processes thru canaliculi (tunnels) § Maintain mature matrix during life § Help control Ca and phosphate levels § Mechanotransduc9on: detect mechanical forces and translate into biologic ac7vity (they’re director cells) Osteoid § Organic component of the ECM § Type 1 collagen + other proteins Bone matrix % § Osteoid: organic 35% § Hydroxyapa7te: Inorganic crystalline mineral component (65%) Woven and lamellar § Woven: produced rapidly (fetal dev, repair) = haphazard collagen arrangement § Lamellar: produced slower, parallel collagen fibers w/ high structural integrity Endochondral ossifica9on principles * (car7lage to boneà longitudinal bone growth) § Mesenchymal precursor cells lay down car9lage mold (anlagen) for bone deposi7on § Car7lage replaced by bone in the presence of capillaries – BLOOD is the pre-req for BONE § The central por7on of the anlagen is resorbed, crea7ng the medullary canal. § Simultaneously, at midshaR (diaphysis), osteoblasts begin to deposit the cortex beneath the periosteum producing the primary center of ossifica7on and growing the bone radially. § At each longitudinal end (epiphysis), endochondral ossifica7on proceeds in a centrifugal fashion (secondary ossifica7on center). § Eventually, a plate of car9lage becomes entrapped between the two expanding centers of ossifica7on, forming the PHYSIS or GROWTH PLATE. § The chondrocytes within the growth plate undergo sequen7al prolifera9on, hypertrophy, and apoptosis. § In the region of apoptosis, the matrix mineralizes and is invaded by capillaries, providing the nutrients for osteoblasts, which synthesize osteoid. This process produces longitudinal bone growth. Physis (epiphyseal growth plate) * § Plate of car9lage between 2 expanding centers of ossifica7on (the diaphysis & epiphysis centers) § Chondrocytes within the growth plate undergo sequen7al prolifera7on, hypertrophy, and apoptosis § In region of apoptosis, the matrix mineralizes and is invaded by capillaries, providing the nutrients for osteoblasts, which synthesize osteoid à produces longitudinal bone growth Metaphysis * § Where epiphysis meets diaphysis; in growing bone: region with the epiphyseal growth plate Epiphysis * § Longitudinal end of long bone § Secondary ossifica7on located here Diaphysis * § The midshaa of the long bone § Primary ossifica7on located here Four zones of growing end (IMAGE TO LABEL) § Zone of res9ng/reserve car9lage – anchors the plate (on end of bone) to the epiphysis and contains immature chondrocytes, as well as delicate blood vessels that penetrate it from the diaphysis and bring nourishment to the en7re plate § Zone of prolifera9on – young prolifera7ng car7lage – site of most ac7ve inters77al growth of the car7lage cells, which are arranged in ver7cal columns § Zone of matura9on – maturing car7lage – reveals a progressive enlargement and matura7on of the car7lage cells as they approach the metaphysis. These chondrocytes accumulate glycogen in their cytoplasm and produce phosphatase which is involved in the calcifica7on of their surrounding matrix. § Zone of calcifica9on (hypertrophy?) – calcifying car9lage is thin, and its chondrocytes have died as a result of calcifica7on of the matrix. This is structurally the weakest zone of the epiphyseal plate. Bone deposi7on is ac7ve on the metaphyseal side of this zone and as new bone is added to the calcified cores of car7lage, matrix, the metaphysis becomes correspondingly longer. Intramembranous * (apposi9onal growth) § § § § mesenchymal cells to OSTEOBLASTS and lay down bone w/out car7lage map develops flat bone bone grows in width/girth via apposi9onal growth from the osteoblasts in the deep, or inner (cambium), layer of the periosteum while simultaneously, the medullary cavity becomes larger through osteoclas7c resorp7on of bone on the inner surface of the cortex, which is lined by endosteum § Bones of the cranium are formed by osteoblasts directly from a fibrous layer of 7ssue, without car7lage anlagen. The enlargement of flat bones is achieved by deposi7on of new bone on a preexis7ng surface. Cranium: fibrous 7ssue layer à bone; flat bone enlargement via new bone deposited onto pre-exis7ng surface Bone modeling * § endochondral ossifica7on: bones grow in length § intramembranous ossifica7on: grow in width/girth (neurocranium/vault) § The physis provides growth in the length of the metaphysis of a long bone. In this site of growth, a constant balance is maintained between two separate processes: o Inters99al growth of car7lage cells of the plate, making it thicker and thereby moving the diaphysis farther away from the metaphysis o Calcifica9on: death and replacement of car7lage on the metaphyseal surface by bone through endochondral ossifica7on Bone remodeling * § metaphyseal ends must remodel as epiphysis moves away from diaphysis; occurs via simultaneous osteoblas9c bone deposi7on on one surface and osteoclas9c resorp7on on opposite surface - must be in balance § con7nues throughout life § Growing years: deposi9on exceeds resorp7on = posi9ve bone balance § Peak bone mass in early adulthood aaer cessa7on of skeletal growth; a set-point determined by many factors: polymorphisms in the vitamin D and LRP5/6 receptors, nutri7on, and physical ac7vity § Old age (begin 4th decade): resorp9on exceeds deposi7on = nega9ve bone balance (slow decline in bone mass) Wolf’s law § Remodeling occurs at sites experiencing physical stress; resorp7on in areas w/ li^le stress § exemplified by marked cor9cal thickening on the concave side of a curve bone as well as by the alignment of trabecular systems along the lines of weight bearing stress in the internal architecture Protein Calorie/Energy Malnutri9on (PCM or PEM) § most common cause of retarded longitudinal bone growth (endocrine func7on disturbances also present) § Human growth hormone (HGH), synthesized in anterior pituitary gland, exerts its growth-promo7ng effect through the produc7on of insulin-like growth factors in the liver § Thyroxine is also essen7al for normal longitudinal growth § Sex hormones are involved in the characteris7c post-pubertal “growth spurt” in adolescent children Bone Mul9cellular Unit (BMU) § unit of coupled osteoblast and osteoclast ac7vity on the bone surface where remodeling occurs