Front Matter

Chapter 3 Musculoskeletal Structure and Physiology 57

that are immobilized through their association
with other components of the bone matrix
(Kim et al., 2011).
The major cells in bone include osteoblasts,
osteocytes, and osteoclasts. Osteoblasts are
osteogenic cells that reside within periosteal
and endosteal membranes. They are a
heterogeneous population of cells representing
various stages of differentiation including mes­
enchymal stem cells, osteogenic progenitors,

preosteoblasts, and osteoblasts. Mesenchymal

stem cells and osteogenic progenitor cells are

capable of self‐replication, which is important

for maintenance of a pool of progenitors that

can participate in osteosynthesis during

growth, physiological remodeling, and healing

of bone. Osteoblasts are responsible for biosyn­

thesis, deposition, and mineralization of bone

matrix, as well as synthesis and secretion of

growth factors and biological mediators that

are deposited within the matrix during bone

formation. Osteocytes are terminally differenti­

ated bone cells that form as osteoblasts become

surrounded by bone matrix during osteosyn­

thesis. In mature bone, osteocytes reside within

lacunae within the concentric lamellae of a

Haversian unit. They communicate with

neighboring osteocytes and osteoblasts by

direct contact via long cytoplasmic projections

that extend through canaliculi within the bone

matrix. Osteoclasts are multinucleated cells

derived from hematopoietic precursors; they

resorb bone matrix.

The tightly packed crystalline organization

of bone mineral imparts high stiffness and

strength. Bone is nevertheless a highly aniso­

tropic material that is able to withstand large

compressive loads but is comparatively weak

when subjected to tensile stress. Compressive

loads are borne by the mineral component of

Haversian system

Circumferential

osteonal lamellae

Central canals

Endosteal vasculature

Tr abecular bone

Figure 3.9 Structural organization of bone.

Figure 3.10 Cancellous bone is composed of thin bony
shelves, or trabeculae (T), covered with an endosteal
membrane (E).