Bones and Joints Flashcards
Primitive osteoprogenitor cells of mesenchymal origin develop into all of the following cell types in bones except: A. osteoblasts B. osteocytes C. lining cells D. osteoclasts
D. osteoclasts. Osteoclasts are derived from hematopoietic stem cells of the macrophage line
Which transcription factor guides development of mesenchymal cells into osteoprogenitor cells?
Runx2 ( runt-related transcription factor 2)
SOC5, 6 and 9 are responsible for development of which cell type?
Chondrocytes
PPAR-gamma2 (peroxisome proliferator activator receptor) is responsible for development of which cell type?
Adipocytes
Osteoblasts develop under signaling from which transcription factors?
Runx2, osterix, beta-catenin
Functional roles of osteoblasts include?
manufacturing osteoid, initiate mineralization, mediate both bone resorption and formation, produce regulatory factors deposited in the bone matrix
Bone lining cells are inactive versions of what cells?
osteoblasts
Which type of bone cell is responsible for lining the endosteal surface of bone and forming the functional barrier between the extracellular fluid compartment of bone tissue and surrounding tissues?
bone lining cells, most abundant cell type in the endosteal skeleton. Form barrier between osteoclasts precursors and bone surface.
What cells are responsible for the bone-blood barrier, controlling the movement of ions in and out of the extracellular fluid?
bone-lining cells
What is an osteoblast marker expressed by bone-lining cells during active remodeling?
RANKL ( receptor activator of nuclear factor kappa B ligand)
When does an osteoblast become and osteocyte?
When it surrounds itself with osteoid and resides in lacunae in the mineralized matrix
How do osteocytes maintain contact with other osteocytes, osteoblasts and bone-lining cells?
Through a network of branching cytoplasmic processes called canaliculi
What key regulatory factors for bone resorption and formation are produced by osteocytes?
sclerostin, RANKL, fibroblast growth factor 23 (FGF23), All produced under control of PTH
What is the function of increased RANKL expression by osteocytes?
Osteoclastic bone resorption
What is the function of FGF23 expression by osteocytes?
phosphate homeostasis –> phosphate excretion from the kidney
What are the key factors involved in osteoclast formation?
macrophage colony stimulating factors and RANK (not RANKL - that’s produced by osteoblasts and osteocytes). RANKL from osteoblasts/cytes allows fusion of osteoclast precursors to form the mature osteoclast.
IHC for which antigen can be useful to identify osteoclasts?
TRAP (tartrate resistant acid phosphatase)
Howship’s lacunae are shallow pits on bone surfaces containing what?
mature osteoclasts. Their presence indicates previous resorption even if the osteoclast is gone.
What factors can enhance osteoclast survival?
Inflammatory cytokines like TNF-a and IL-1 as well as PTH. Explains why osteoclasts are found within medullary spaces filled with fibrous tissue
What type of collagen is found in bone?
Type I collagen. Also the main collagen found in tendons, ligaments, ocular sclera and dentin
The enzyme lysyl oxidase which is responsible for the intermolecular cross-links in collagen, form with the assistance of what mineral?
Copper
What noncollagenous protein is produced by osteoblast, found in bone and is responsible for interacting with both type I collagen and hydroxyapatite?
Osteonectin or SPARC. May be important in intramembranous bone formation post-fracture
The production of osteocalcin (or bone-Gla protein) by osteoblasts is dependent on what vitamin? What vitamin causes an increase in its synthesis?
dependent on Vitamin K, Vitamin D increases synthesis
What is the function of osteocalcin in bone formation?
when carboxylated, osteocalcin is deposited in osteoid before mineralization and allows strong binding to calcium
What are four noncollagenous proteins found in bone?
Osteonectin, osteocalcin, osteopontin and bone sialoprotein
What kinds of mineral does bone contain?
Ca, Phosphate, carbonate, magnesium, sodium, zinc, flouride
What protein is associated with ectopic bone mineralization?
matrix Gla-protein
What structures composed of extracellular organelles originating from cytoplasmic blebs from osteoblasts, chondrocytes, and odontoblasts are responsible for initiating the mineralization process?
matrix vesicles
What is the key event in the initiation of mineralization?
Alteration in the phosphate to inorganic pyrophosphate ratio through the enzymes ALP and ENPP1 (inorganic pyrophosphate and osteopontin normally inhibit mineralization). Upregulation of ALP is most important, increased phosphate.
Osteoid becomes mineralized approximately how many days after deposition?
5-10 days, results in the osteoid seam which is separated from mineralized bone by a basophilic linear mineralization front
What is woven bone characterized by ultrastructurally?
collagen fibers arranged in a haphazard, interwoven fashion
Wnt signaling is involved in which types of skeletal development?
All - craniofacial, limb, joint
Suture formation in the skull bones is regulated by which transcription factors?
FGFR1, 2, 3; TGF-beta1,2,3;
During endochondral ossification, the developing fetus chondrocytes are controlled by which transcription factor?
SOX9
What are the 3 zones of hyaline cartilage at the growth plate?
Reserve (i.e. resting) zone, proliferative zone, zone of hypertrophy
What type of collagen is found within cartilage of the resting zone?
Type II collagen
What zone of cartilage does mineralization occur?
The deepest part of the zone of hypertrophy
What structure is responsible for increasing the diameter of the physis during growth?
The ossification groove of Ranvier, contains progenitor cells
The lattice of trabeculae with a basophilic core of mineralized cartilage covered by a thin, eosinophilic layer of bone is termed?
primary spongiosa
Osteoclast formation is regulated by which 3 pathways?
RANK/RANKL - stimulates osteoclast formation; Wnt-betacatenin - stimulated osteoclast formation; Jagged 1/Notch 1 - inhibits osteoclast formation
What ratio is important in regulating osteoclast formation?
The ratio of RANKL to OPG (osteoprotegerin) which is a decoy of RANK. The RANKL-RANK binding (as well as some inflammatory conditions not associated with RANK/RANKL) is what leads to osteoclast production.
Pathogenesis of bone resorption
bone lining cells retract from the endosteal surface of bone, secrete enzymes to digest unmineralized bone and expose mineralized bone –> osteocyte apoptosis secondary to mechanical stress lead neighboring osteocytes to express RANKL and M-CSF–> sclerostin from osteocytes inhibits osteoblasts –> osteoclast precursors are recruited from RANKL/M-CSF –> differentiate into osteoclasts and resorb bone, then undergo apoptosis –> pre-osteoblasts are recruited, secrete PTHrP to stimulate differentiation and suppress apoptosis –> Wnt-B-catenin, BMPs and TGF-beta stimulate bone formation, mineralization and quiescence.
What is the difference between a resting cement line and a reversal line?
Resting cement line is a site where bone formation ceased for awhile then started again, whereas reversal lines are sites where bone resorption actually occurred and now bone formation has restarted
What is the most sensitive clinical pathology marker of bone formation?
Plasma osteocalcin, it is proportional to the rate of osteoid synthesis.
What markers are used for bone resorption?
tartrate-resistant acid phosphatase isoform 5b (TRAP 5b) and several breakdown products of Type I collagen : serum carboxyterminal telopeptide of type I collagen (ICTP), urinary hydroxyproline, pyridinoline (PYD), deoxypyrodinoline (DPD).
What are apophyses?
Growth plates subjected to primarily traction forces, consist of fibrocartilage. Example is the lesser trochanter of the femur.
What are common causes of angular limb deformities in foals?
Physiologic, hypothyroidism, sepsis
What does Codman’s triangle refer to?
A cone-shaped region of new bone beneath the periosteum that occurs in cases of osteosarcoma and osteomyelitis
Multiple microfractures involving several adjacent trabeculae without gross displacement of the bone ends are referred to as?
infractions; seen in bones weakened by disease that still bear weight
What is the most common site of a stress fracture in young racehorses?
dorsal or dorsomedial cortex of the 3rd metacarpal (cannon bone)
What is the histologic feature of a bucked shin in a horse and what breeds of horses are most affected?
Smoothly contoured foci of periosteal new bone on the dorsal surface of the cannon bone. QH and Thoroughbreds (racing breeds)
What condition is linked to bucked shins in horses and may be a sequela?
Saucer (incomplete) fractures of the dorsal cortex of the cannon bone.
Osteogenesis imperfecta is a disorder of what type of collagen?
Type I collagen, characterized by osteopenia and excessive bone fragility
Chondrodysplasias result in what type of dwarfism?
disproportionate
Dexter bulldog calves result from homozygosity of a gene with what type of expression pattern? What is the gene associated with Dexter calf chondrodysplasia?
incomplete dominance; ACAN (aggrecan) gene
What is the histologic feature of the physis in a Dexter bulldog calf?
lack of a distinct growth plate with densely packed chondrocytes showing no orderly arrangement into columns and a fibrillar eosinophilic intercellular matrix surrounding large vascular cartilage canals. No distinct primary or secondary spongiosa.
What are the four subtypes of chondrodysplasia in cattle?
Bulldog, Telemark, “snorter” and long-headed
Holsteins with bulldog chondrodysplasia have parents that are phenotypically normal. True/false
True. The parents are heterozygous and the gene is an autosomal recessive pattern of inheritance.
What is the histologic difference between snorter dwarfism and bulldog dwarfism?
In snorter dwarfism, the growth plate has three distinct zones but they are all shorter and more irregular with fewer hypertrophied chondrocytes
What breeds of sheep are susceptible to spider lamb syndrome?
Suffolk and Hampshire
What is the histologic feature of spider lamb syndrome?
Multiple, irregular, small ossification centers surrounded by persistent bands of cartilage
What is the mutation in spider lamb syndrome?
Point mutation in FGFR3, expressed in resting and proliferating chondrocytes and limit # of chondrocytes that enter hypertrophy phase
What type of disproportionate chondrodysplasia in sheep leads to chondrolysis which coalesce to form clefts and cystic spaces surrounded by concentric rings of granular and basophilci fibrillar matrix in areas of both articular and physeal cartilage?
Texel sheep
Mutations in the ACAN gene have shown to result in chondrodysplasia in what two species?
cattle and miniature horses
What breeds of dogs have pathologic chondrodysplastic syndromes?
Alaskan malamute, norwegian elkhound, karelian bear dog, English pointer, Great pyrenees
Osteogenesis imperfecta types 1 through 4 is a mutation in which genes? What is the pattern of inheritance?
COL1A1 or COL1A2 (code for a1 and a2 chains of Type i collagen respectively); autosomal dominant
Osteogenesis imperfecta is most common in what 2 species?
cattle and sheep
What is the histologic feature of osteogenesis imperfecta?
basophilic spicules of woven bone and minimal compaction by the addition of lamellar bone interspersed with loose mesenchymal tissue
What is the defect in Belgian blue cattle with dermatosparaxis?
deficiency in enzyme that converts procollagen to collagen, results in SKIN FRAGILITY not found in OI cases.
This disease, otherwise known as marble bone disease, is characterized by defective osteoclast bone resorption and dense, unresorbed cones of primary spongiosa in the bone marrow that extends from the metaphysis to the center of the diaphysis
Osteopetrosis
Osteoclasts are normally present in [low/normal/abundant/all of the above] numbers in osteopetrosis.
All of the above. The defect in some disorders is in the inability of osteoclasts to resorb bone due to a defective proton pump or chloride channel mutation that interfere with acidification of osteoclasts. The defect in other disorders is in RANKL which guides differentiation of osteoclasts leading to reduced #’s of osteoclasts.
What breed of cattle is most affected by osteopetrosis?
Angus. The gene in red Angus is SLC4A2 which helps acidify the osteoclast. Not in black Angus.
What is a hematopoietic sequelae of osteopetrosis?
extramedullary hematopoiesis in the liver
Are growth plates normal or abnormal in osteopetrosis?
Normal. The defect is in the metaphysis and diaphysis.
Osteopetrosis is associated with which viral diseases?
BVDV, feline leukemia virus, canine distemper virus
Radiating trabeculae of bone extending from the cortical bone to a thickened periosteum is the histologic feature of what disease?
congenital hyperostosis in piglets
Which of the following bones are most affected by congenital hyperostosis? A. humerus B. radius C. vertebral body D. mandible
B. The radius and ulna are the most affected bones in congenital hyperostosis in piglets. The axial skeleton is not affected at all in C.H.
Schistosomus reflexus comprises all of the following congenital defects except:
A. lordosis
B. dorsal reflection of the limbs and pelvic bones
C. pectus excavatum
D. nonunion of the pelvic symphysis
C. pectus excavatum is not a classic component of schistosomus reflexus