Interstitial lamellae groups of incomplete lamellae

• Interstitial lamellae: groups of
incomplete lamellae which lie between
osteons; these are remains of old
osteons cut through by bone remodeling
• Circumferential lamellae: extends
around the entire circumference of the
diaphysis
55
Figure 6.7
(a)
Compact bone
Endosteum lining
bony canals and
covering trabeculae
Perforating
(Volkmann ± s)
canal
Perforating (Sharpey ± s) fibers
Periosteal blood vessel
Periosteum
Lamellae
Circumferential
lamellae
Osteon
(Haversian system)
Central
(Haversian) canal
Spongy bone
(c)
Interstitial
lamellae
Lacunae
Lamellae
Central
canal
Lacuna (with
osteocyte)
(b)
Nerve
Vein
Artery
Canaliculi
Osteocyte
in a lacuna
Lacunae
Lamellae
Central canal
Microscopic Structure of Compact Bones
56
Microscopic Structure of
Spongy Bone
• Less complex than compact bone
• Trabeculae are too small to contain
osteons or its own blood vessels
• Trabeculae contain several layers of
lamellae and osteocytes
• Osteocytes receive nutrients from
capillaries in the endosteum surrounding
the trabeculae via connections through
the canaliculi
57
Trabecula
Osteocytes
Endosteum
Marrow
space
(b)
(a)
Osteoblasts
Microscopic Structure of Spongy Bones
Figure 6.9
58
Ossification (osteogenesis):
bone-tissue formation
• Membrane bones (e.g. cranial bones,
clavicles)—form directly from mesenchyme
through intramembranous ossification
without first being modeled in cartilage
• Endochondrial bones — develop initially
from hyaline cartilage which is replaced by
bone through a process called
endochondral ossification
59
Intramembranous Ossification
Figure 6.10, steps 1–2
Mesenchymal
cell
Collagen
fiber
Ossification
center
Osteoid
Osteoblast
Osteoid
Osteocyte
Newly calcified
bone matrix
Osteoblast
Ossification centers appear in the fibrous
connective tissue membrane.
• Selected centrally located mesenchymal cells cluster
and differentiate into osteoblasts, forming an
ossification center.
Bone matrix (osteoid) is secreted within the
fibrous membrane and calcifies.
• Osteoblasts begin to secrete osteoid, which is
calcified within a few days.
• Trapped osteoblasts become osteocytes.
1 2
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Intramembranous ossification
• Ossification center appears in fibrous
connective tissue membrane where
mesenchymal cells differentiate into
ostoblasts
• Osteoblasts secrete osteoid (bone matrix)
within fibrous matrix which calcifies; ± trapped ²
osteoblasts become osteocytes
• Woven bone (network of trabeculae) and
periosteum form
• Compact lamellar bone replaces woven bone
just deep to periosteum and red marrow appears
in spongy bone (diploe)
61
Intramembranous Ossification
Figure 6.10, steps 3–4
Mesenchyme
condensing
to form the
periosteum
Blood vessel
Trabeculae of
woven bone
Fibrous
periosteum
Osteoblast
Plate of
compact bone
Diploë (spongy
bone) cavities
contain red
marrow
Woven bone and periosteum form.