Chapter 6: Bones and skeletal tissues (part b) provides knowledge of bone development, bone homeostasis, homeostatic imbalances of bone and developmental aspects of bones. After completing this chapter, students will be able to: Compare and contrast intramembranous ossification and endochondral ossification, describe the process of long bone growth that occurs at the epiphyseal plates,.and other contents. | 6 Bones and Skeletal Tissues: Part B Bone Development Osteogenesis (ossification)—bone tissue formation Stages Bone formation—begins in the 2nd month of development Postnatal bone growth—until early adulthood Bone remodeling and repair—lifelong Two Types of Ossification Intramembranous ossification Membrane bone develops from fibrous membrane Forms flat bones, . clavicles and cranial bones Endochondral ossification Cartilage (endochondral) bone forms by replacing hyaline cartilage Forms most of the rest of the skeleton Figure , (1 of 4) Mesenchymal cell Collagen fiber Ossification center Osteoid Osteoblast Ossification centers appear in the fibrous connective tissue membrane. • Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center. 1 Figure , (2 of 4) Osteoid Osteocyte Newly calcified bone matrix Osteoblast 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. 2 Figure , (3 of 4) Mesenchyme condensing to form the periosteum Blood vessel Trabeculae of woven bone Woven bone and periosteum form. • Accumulating osteoid is laid down between embryonic blood vessels in a random manner. The result is a network (instead of lamellae) of trabeculae called woven bone. • Vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum. 3 Figure , (4 of 4) Fibrous periosteum Osteoblast Plate of compact bone Diploë (spongy bone) cavities contain red marrow Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears. • Trabeculae just deep to the periosteum thicken, and are later replaced with mature lamellar bone, forming compact bone plates. • Spongy bone (diploë), consisting of distinct trabeculae, per- sists internally and its vascular tissue becomes red marrow. 4 Endochondral Ossification . | 6 Bones and Skeletal Tissues: Part B Bone Development Osteogenesis (ossification)—bone tissue formation Stages Bone formation—begins in the 2nd month of development Postnatal bone growth—until early adulthood Bone remodeling and repair—lifelong Two Types of Ossification Intramembranous ossification Membrane bone develops from fibrous membrane Forms flat bones, . clavicles and cranial bones Endochondral ossification Cartilage (endochondral) bone forms by replacing hyaline cartilage Forms most of the rest of the skeleton Figure , (1 of 4) Mesenchymal cell Collagen fiber Ossification center Osteoid Osteoblast Ossification centers appear in the fibrous connective tissue membrane. • Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center. 1 Figure , (2 of 4) Osteoid Osteocyte Newly calcified bone matrix Osteoblast Bone matrix (osteoid) is secreted within the fibrous membrane and calcifies. • Osteoblasts begin to .
