Bone Histology

Question 1

Lamellar bone

Answer 1

Mature/secondary bone
Regular parallel arrangement of collagen fibers
Most adult bones

Question 2

Woven bone

Answer 2

Immature/primary - usually replaced by lamellar bone
Loose arrangement of collagen fibers
Lower mineral content, more cells
Forms during fracture repair/remodeling

Question 3

Epiphysis

Answer 3

Knobby regions at end of bone

Compact bone is superficial, with spongy bone deep to surface - contains epiphyseal plat

Question 4

Metaphysis

Answer 4

Between diaphysis and epiphysis

Consists of spongy bone

Question 5

Epiphyseal line

Answer 5

Within metaphysis

Epiphyseal plate has fused

Question 6

Medullary cavity

Answer 6

Cylindrical shape in diaphysis containing bone marrow

Question 7

Periosteum

Answer 7

Dense irregular CT covering external surface. Does not cover articular surfaces
Anchored in perforating fibers
Neurovascular
Contains osteoblasts

Question 8

Endosteum

Answer 8

CT lining of medullary cavity

Contains osteoprogenitor cells, reticular cells, CT Uber’s

Question 9

Periosteum layers

Answer 9

Inner layer: osteoprogenitor cells next to mature bone - retain potential for bone injury and repair
Outer layer: rich in vasculature, fibroblasts and collagen fibers
Sharpey’s fibers

Question 10

Sharpey’s fibers

Answer 10

In the outer layer of periosteum, these fibers anchor to outer circumferential lamellae

Question 11

Bone matrix

Answer 11

Organic components: type I collagen fibers, proteoglycans, other proteins (osteocalcin, osteopontin, osteonectin)
Inorganic components: Ca hydroxyapatite, Mg, K, Na, F

Question 12

Osteon

Answer 12

Cylindrical structures in mature compact bone - run parallel to the shaft of the bone

Question 13

Canals

Answer 13

Central - vasculature and innervation
Perforating canals - perpendicular connections to central canal
Canaliculi - connect lacunae

Question 14

Lamellae

Answer 14

Concentric: rings of bone around central canal
Outer circumferential - rings around periosteum
Inner circumferential - rings around endosteum
Interstitial: pieces of old osoteon that result from remodeling

Question 15

Osteoprogenitor

Answer 15

Stem cell that produces osteoblasts

Found in endosteum and periosteum

Question 16

Osteoblasts

Answer 16

Mesenchymal cells that produce osteoid (nonmineralized organic matrix)
Initiate and control mineralization of the osteoid

Question 17

Osteocytes

Answer 17

Mature bone cells embedded in bone matrix
Maintain matrix
Communicate with osteoblasts to increase deposition of bone matrix

Question 18

Osteoclasts

Answer 18

Large, multinucleated cells produced by the fusion of monocytes
Ruffled border
Remodel and reabsorb bone through H+ and lysosomal proteins

Question 19

Intramembranous ossification

Answer 19

Bones develop from mesenchyme precursors 
Select bones form from this process 
Flat 
Some facial
Mandible
Central part of clavicle

Question 20

Endochondral ossification

Answer 20

Begins with hyaline cartilage 
Produces most bones of the skeleton 
Bones of extremities
Pectoral and pelvic girdles 
Pelvis, vertebrae, ends of clavicle

Question 21

Reserve zone (endochondral ossification)

Answer 21

Primitive hyaline cartilage - responsible for lengthening - cells run

Question 22

Proliferative zone ( endochondral zone)

Answer 22

Chondrocytes cluster parallel to growth axis

Share territorial matrix

Question 23

Hypertrophic zone (endochondral ossification)

Answer 23

Hypertrophic chondrocytes form calcified matrix - chondrocyte apoptosis - attract vasculature - instruct bone collar

Very important zone for signaling

Question 24

Vascular invasion zone (endochondral ossification)

Answer 24

Vasculature penetrates calcified atria (septa) - invasion of osteoprogenitor

Question 25

Achondroplasia

Answer 25

Autosomal dominant syndrome - mutation in FGFR3 (fibroblast growth factor receptor 3) 
Most common form of dwarfism 
Shortening of long bones 
Small midface 
Altered spinal curvature

Question 26

Osteomalacia

Answer 26

Progressive softening and bending of bone 
Defect results in decreased mineralization of osteoid 
Caused by: dietary vitamin D deficiency 
Lack of sun exposure 
GI disease (US) 
Signs: bone and joint pain 
Muscle weakness 
Fracture 
Difficulty walking and waddling gait 
Muscle spasms and cramps

Question 27

Rickets

Answer 27

Juvenile osteomalacia
Defect in mineralization of cartilage in growth plate
Vitamin D deficiency, decreased absorption of calcium and phosphorus from bowels
Caclipenic - Ca deficiency
Signs of rickets
Delayed closure of fontanelles
Parietal and frontal bossing
Craniotabes (soft skull bones)
Widening of wrist and bowing of the distal radius and ulna
Progressive bowing of femur and tibia