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4. What are the differences between cortical and trabecular bone?

The differences between cortical and trabecular bone are summarized in the

table given below.

Parameters Cortical Trabecular

Synonyms Compact bone Cancellous, spongy

Contribution to total bone mass 80 % 20 %

Predominant sites Shaft of long bones End of long bones, vertebra

Porosity 5–15 % 30–90 %

Haversian system Present Absent

Metabolic activity Low High

Remodeling rate Low High

Predominant hormonal control PTH, thyroxine Gonadal steroids, glucocorticoids

5. What are the differences between woven and lamellar bone?
   The differences between woven and lamellar bone are summarized in the table
   given below.

Parameters Woven bone Lamellar bone

Architecture Disorganized collagen Organized collagen (parallel or

concentric)

Cell-to-matrix ratio High Low

Bone turnover High Low

Strength Weak Strong

Formation Formed by rapid osteoid

production by osteoblast

Formed by maturation of woven

bone

Sites Fetal bone

Site of fracture in adults

Paget’s disease

All bones in the adult

6. How is bone formed?

New bone is formed by either endochondral or intramembranous ossifica-

tion. Endochondral ossification is a stepwise integrated process of bone for-

mation involving differentiation of mesenchymal stem cells into cartilage

that forms a scaffolding for deposition of bone matrix by osteoblasts.

Intramembranous ossification involves direct formation of bone from mes-

enchymal stem cells without intermediate stage of cartilage formation. The

flat bones (craniofacial) are formed by intramembranous ossification, while

vertebrae, ribs, and long bones are developed by endochondral ossification

(Fig. 5.3).

5 Rickets–Osteomalacia