Interstitial lamellae groups of incomplete lamellae which lie between osteons

Interstitial lamellae groups of incomplete lamellae

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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 60
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6/26/19 11 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.
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