Osteogenesis Flashcards

Question

bony matrix consists of ?

Answer 1

• Composed of 1.Ground substance & 2. Fibers 1. Ground substance i. Organic matter includes - proteoglycan - several glycoprotein ii. Inorganic matter - mainly calcium (99% of body calcium)& phosphorus(80% of body phosporus) - others include bicarb., citrate, magnesium, potassium & sodium 2. fibers - almost all collagen type 1 Note: inorganic – 70%, organic – (mainly collagen) 30% - inorganic matters (minerals) - Rigidity & strength (Hardness) - organic matters (collagen) - Resist breaking

Answer 2

• Osteoporosis - reduction in bone mass most often in elderly - predisposes to fractures particularly femoral neck, wrist & vertebrae. DEXA= Bone density determination test • Osteomalacia [painful condition] -bone is soft & prone to fracture -failure of mineralisation of Osteoid -maybe due to inadequate intake in diet - malabsorption - kidney disease in which loss of phosphate in urine • Osteogenesis imperfecta (brittle bone disease) - skeletal fragility -deficiencies in synthesis of type I collagen

Answer 3

• Periosteum & endosteum -outer dense fibrous connective tissue - inner cellular containing osteogenetic cells function -nutrition of osseous -provision of continuous supply of nee osteoblast for bone growth and repair

Answer 4

i. Outer layer - collagen fibres & fibroblasts Sharpey’s fibres -bundles of collagen fibres penetrate the bone matrix -binds periosteum to bone -Inner layer more cellular -composed of Osteoprogenitor cells (fibroblast like) with potential to divide & differentiate into osteoblasts Note ; Osteoprogenitor cells play important role in bone growth & repair

Answer 5

It lines -inner surfaces of bone (marrow cavity), - the vascular canals - & trabeculae (of spongy bone) - composed of single layer of Osteoprogenitor cells & very small amount of connective tissue

Answer 6

• A. Primary/ immature /woven or fetal bone - is formed either directly from mesenchymal t/s.(membranous ossification) or from cartilagenous model (endochondral ossification) • Woven bone - has collagen fibres arranged randomly Woven bone is later replaced by mature or lamella bone B. Secondary/ mature or Lamella bone - by remodeling (by resorption & appositional growth )

Answer 7

Histological feature Collagen - arranged randomly Mineral contents – lower Osteocytes – in higher proportion Site normal i. during fetal bone formation ii. near the sutures of flat bones iii. in tooth sockets iv. at insertions of some tendons pathological conditions where bone are forming rapidly i. in healing of fracture ii. Paget’s disease

Answer 8

Secondary or Lamellar bone matureChararecteristic -Collagen fibres are arranged in lamellae which are i. parallel to each other or ii.concentrically around a vascular canal Macroscopically Classified into 1. Spongy 2. Compact bone

Answer 9

Site • in long bones - at the ends (epiphysis) - in interior (medullary)part of the shaft (diaphysis) in flat bone eg.vault of skull - in diploe (marrow space) b/t.outer & inner tables in short bone -at the central core

Answer 10

Composed of trabeculae spicules of bone Jutting out fr. Internal surface of compact bone into medullary cavity forming - network of trabeculae & - numerous interconnecting cavities

Answer 11

• Microscpic feature • Trabeculae - oriented either parallel to the long - axis of trabecula or - in irregular plates there is no Haversian system - lacunae & osteocytes are scanty • -have thin external coating of endosteum containing • flat inactive osteoblasts • -between the trabeculae of bone are the marrow spaces

Answer 12

• In long bone in the shaft -forms thick ,outer part at the end of long bone -forms a thin outer layer that covering the spongy bone • In Flat bones -forms outer & inner tables • In short bone - completely surrounding the core of spongy bone

Answer 13

Composed of thin layers of bony lamellae • Lamellae are of 4 types i. concentric lamellae of Haversian system - Osteon • ii. inner circum.lamellae - Concentric lamellae lining the inside of compact bone • iii. Outer circum.lamellae - Concentric lamellae at the outermost aspect of compact bone • iv. Interstitial lamellae - Lamellae found b/t.Haversian systems - Old Haversian system left during • the process of growth/remodelling

Answer 14

-Column of long cylinder of bony t/s. -running parallel to longitudinal axis of a (usually ) compact bone -Consist of a Central canal -surrounded by concentric lamellae (4-20) of bony tissue -Haversian canal - central canal of Haversian system lined by endosteum it contains blood vessels, lymphatics & nerves Note ; lacunae containing the osteocytes usually lie b/t. lamellae canaliculi –minute canals interconnected lacunae & have connection with H.canal. - it contains cytoplasmic extensions of Osteocytes

Answer 15

Communicates • Haversian canals to • i. one another • ii. with marrow cavity • iii. & also with periosteum • Pierce lamellae • run oblique or right angle to H.canal

Answer 16

1. Intramembranous 2. Endochondral

Answer 17

– formation of bone directly from mesenchymal t/s – flat bones exp: vault of the skull maxilla cavicle

Answer 18

i. condensation of mesenchymal tissue (from mesoderm or neural crest) from mesenchymal tissue forms ii. Osteoprogenitor cells - these cells differentiate into iii. Osteoblasts -secrete matrix osteoid -osteoblasts trapped inside the lacunae b/c iv. Osteocytes v. Mineralisation of matrix & bone forming centres (ossification centres) are formed vi. • Ossification centres grow radially • & finally fused together

Answer 19

1. formation of Primary ossification centre 2. formation of Secondary ossification centre • Formation of bone from (continuously growing) cartilage model • by deposition of bony matrix on preexisting cartilage matrix • eg. long bones • base of the skull •vertebrae -pelvis

Answer 20

• i. Formation of hyaline cartilagenous model a. mesenchyme begins.to condense & cells differentiate to form cartilage cells • • b. by the end of 6th.wk. hyaline cartilage model is formed by the chondrocytes ii. Mineralisation of cartilagenous matrix at the central (diaphysis) portion of cartilage model a. Chondrocytes enlarge & degenerate. b. followed by calcification of cartiilage matrix iii. Formation of bone collar • - mean while a thin layer of bone (bone collar) is formed around surface of the shaft • by osteoprogenitor cells of perichondrium (ie. by intramembranous ossification) iv. Formation of spaces (alternating) with calcified cartilagenous matrix • now instead of solid hyaline cartilage the central portion of developing bone is filled with a. remnants of calcified cartilagenous matrix & • b. interconnecting spaces left by degenerated chondrocytes v. Invasion of blood vessel into the spaces left by dead cartilage cells & Osteoblasts formation a. blood vessels with primitive mesenchymal cells (fr. perichondrium) penetrate through bone collar & b. invade the spaceleft by degenerated cartilage cells c. Primitive mesenchymal cells differentiate into Osteoblasts & blood forming cells of bone marrow V. d. Osteoblasts adhere to calcified matrix vi. Formation of Primary ossification centre - bony matrix formation & calcification -Osteoblasts adhered to calcified cartilagenous matrix a. lay down the bony matrix b. followed by calcification -& thus form Primary/woven bone around the calcified cartilage matrix -the osteoblasts trapped in calcified bony matrix b/c osteocytes Endochondral ossification, Secondary ossification centre Secondary ossification centres appear at the ends (epiphyses) of long bone with • regressive changes in Cartilage • & bone formation • similar to diaphysis. • Generally secondary ossification centres appear after birth [within the first 5 years] Mature bone formation the woven/primary bones & calcified carti.matrix are later replaced by lamellar bones • by remodelling so that mature • bone finally consists of • Compact outer layer & • medulla of spongy bone in adult

Answer 21

the centre of hyaline cartilage model solid hyaline cartilage is replaced by a.Calcified matrix b.Spaces left by dead Chondrocytes

Answer 22

ii. epiphysial plate responsible for growth in length of the bone by proliferation of new cartilage cells -On reaching maturity hormonal changes inhibit further proliferation of cartilage cells & -epiphysial growth plate is finally replaced by bone & no more growth in length Age determination in medicolegal cases [ X Ray] generally It is complete about the age of 20.

Answer 23

– Kidneys • Determinesbloodcomposition – Digestive system • Via proteins, Vitamin A, D, C – Female reproductive system • Pregnancy can alter bones [hormonal levels] – Liver • Enzymes-alkaline phosphatase, glycogen

Answer 24

– Pituitary [GH-growth hormone] – Thyroid hormone-osteogenesis/osteolysis [bone destruction] – Androgens and Oestrogens of gonads- bone growth and closure of epiphyseal plates – Unbalanced cortisol and calcitonin may cause osteoporosis

Answer 25

Zone of Reserve cartilage -hyaline cartilage with small clusters of chondrocytes Zone of Proliferation -cartilage cells proliferate by mitosis & form columns of chondrocytes Zone of Maturation -chondrocytes enlarge - no more cell division Zone of Hypertrophy & calcification -chondrocytes b/c.vacuolated -stop secretion of collagen & proteoglycan -instead it secretes alkaline phosphatase & matrix calcified Zone of Degeneration -chondrocytes degenerate, creating cavities in lacunae -lacunae of calcified matrix invaded by capillaries Osteogenic zone -Osteogenic cells differentiate into -Osteoblasts which adhere to the surface of Calcified cartilage spicules & start to form bone

Answer 26

• Cartilage cells in epiphysial plate proliferate continuosly • Chondrocytes b/c mature as they move toward the centre of diaphysis • (& epiphysial growth plates are pushed further apart) thus increases in length • Cells become larger & • Degenerate as they approach the central part of diaphysis • Degenerating zone of cartilage is finally replaced by bone

Osteogenesis Flashcards

(50 cards)