Bone Tissue

University:
Kentucky State University
Course:
BIO 301 | Human Anatomy
Academic year:

2022
Views:

211

Pages:

67
Author:

5prinzg1s

Bone Tissue Functions • Support • Protection (protect internal organs) • Movement (provide leverage system for skeletal muscles, tendons, ligaments and joints) • Mineral homeostasis (bones act as reserves of minerals important for the body like calcium or phosphorus) • Hematopoiesis: blood cell formation • Storage of adipose tissue: yellow marrow Types of Bones: • Gross observation: Compact (cortical) bone: a dense area near the surface, which represents 80% of the total bone mass. Spongy Bone Cancellous (trabecular or spongy) bone: deeper areas with numerous interconnecting cavities, consisting about 20 % of total bone mass. (Trabecular, Cancellous) Compact Bone (Dense, Cortical) Compact bone Spongy bone Types of Bone: • Anatomical: – Long – Short – Flat – Irregular – Sesamoid LONG BONES Head, Proximal end, Epiphysis Shaft , Body, Diaphysis Distal end, Epiphysis LONG BONES Line Spongy Bone Compact Bone Spongy Bone BONE ANATOMY Diaphysis: long shaft of bone Epiphysis: ends of bone Metaphysis: b/w epiphysis and diaphysis Epiphyseal (growth) plate: layer of hyaline cartilage that allows the bone to grow in length The cartilage in the epiphyseal plate is replaced by bone at the age of 18-21, and the resulting bony structure is called the epiphyseal line Epiphysis Metaphysis Epiphyseal line Diaphysis Nutrient artery Articular cartilage: thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms an articulation (joint). Function: reduces friction and absorbs shock. Articular cartilage lacks a perichondrium and lacks blood vessels, repair of damage is limited Periosteum: bone covering (pain sensitive) Sharpey’s fibers: thick bundles of collagen that extend from the periosteum into the bone extracellular matrix Medullary cavity: Hollow chamber in bone - red marrow produces blood cells - yellow marrow is adipose tissue Endosteum: thin layer lining the medullary cavity Diaphysis Epiphysis Metaphysis Epiphyseal (growth) plate/ line Medullary canal (cavity) Compact bone Cancellous (spongy) bone Endosteum: lines the internal surface of bones Periosteum: covers the external surface of bones Compact (cortical) bone  An osteon (or Haversian system): concentric lamellae surrounding a small canal containing blood vessels, nerves, loose CT and lined by endosteum.  Between successive lamellae are lacunae (each with one osteocyte).  The outer boundary of each osteon is called the cement line.  The central canals communicate with the marrow cavity and the periosteum and with one another through transverse Perforating canals (or Volkmann’s canal). Spongy bone lining the medullary canal/ cavity Central canals (or Haversian canals) Transverse Perforating canals (or Volkmann’s canals) Osteon Yellow bone marrow Periosteum Types of lamellae: • • • • Outer circumferential Concentric Interstitial Inner circumferential Concentric lamellae Interstitial lamellae - Scattered among the intact osteons. Are numerous irregularly shaped groups of parallel lamellae. Are lamellae remaining from osteons partially destroyed by osteoclasts during growth and remodeling of bone. Outer and inner circumferential lamellae  Outer circumferential: located immediately beneath the periosteum.  Inner circumferential: located around the marrow cavity. The Structure of Spongy Bone • No osteons • Lighter and porous • Trabeculae – Arches, rods, plates of bone – Branching network of bony tissue – Strong in many directions Spongy bone Trabecular bone tissue (haphazard arrangement) Spaces filled with red and yellow bone marrow Osteocytes get nutrients directly from circulating blood Short, flat and irregular bone is made up of mostly spongy bone Spongy bone PERIOSTEUM & ENDOSTEUM • Surfaces of bone are covered by tissue layers with bone forming cells. • External surfaces: Periosteum. • Internal surfaces: Endosteum. • Functions: – Nutrition of bone. – Continuous supplying of osteoblasts from progenitor cells for bone growth or repair. Endosteum: • Lines the internal cavity of the bone. • Covers trabeculae of spongy bone • Composed of a single layer of flat osteoprogenitor cells. • Has the same functions as periosteum. Periosteum: • Outer fibrous – Some fibers penetrate through bone substance Sharpey’s fibers. • Inner cellular contains osteoprogenitor cells. Short, Irregular, and Flat Bones • Compact bone on the outside with spongy bone (diploë) on the inside • Have no diaphysis or epiphyses • Contain bone marrow between the trabeculae Bone Matrix: • Inorganic matter = ~ 67% of dry weight. – Most of ions are: Ca+2 & PO-4 – Others: Mg, K, HCO3, Citrate. – Ca+2 & PO-4 form C10(PO4)6(OH)2 = hydroxyapatite • Surface ions are hydrated hydration shell – Facilitates fluid exchange • Organic matter = collagen type I & ground substance. Bone cells: Situated inside lacuna Found in both the periosteum and the endosteum Osteoblasts Osteoclasts Bone building cells Bone cutting cells Bone deposition Bone resorption Bone remodeling Osteoprogenitor (osteogenic) Cells • Derived from embryonic mesenchymal cells • Located in the inner cellular layer of the periosteum and in the endosteum. • Have the potential to differentiate into osteoblasts. Osteoblast • Responsible for synthesis of the organic components of the matrix. • Deposition of inorganic components also depends on osteoblasts. • When active, appear cuboidal-columnar, typical protein synthesizing cells. • The newly laid matrix is not calcified and called osteoid. • Osteoblast  Osteocyte Osteoblast  Inactive osteoblasts are flat cells that cover the bone surface. These cells resemble bone lining cells in both the endosteum and periosteum.  Secrete alkaline phosphatase (ALP) and osteocalcin, their circulating levels are used clinically as markers of osteoblast activity.  The newly deposited matrix is not immediately calcified. It stains lightly or not at all compared with the mature mineralized matrix, which stains heavily with eosin.  Because of this staining property of the newly formed matrix, osteoblasts appear to be separated from the bone by a light band.  This band represents the osteoid, the nonmineralized matrix, between the osteoblast layer and the preexisting bone surface Figure 8-3 - Osteogenic cell Osteocyte • Smaller than osteoblasts, almond shaped, with fewer rER, and condensed Golgi. • Situated inside lacuna, one cell in each lacuna. • Cells have processes (filopodial) passing through canaliculi in the thin surrounding matrix. • Adjacent cells make contact through gap junctions in the processes. • Involved in maintenance of matrix. Osteoclast • • • • Large, branched motile, multinucleated cells. Originates from fusion of monocytes. Secretes collagenase and some enzymes. When active, they lie in Howship’s lacuna: – Enzymatically etched depression on the surface. • The surface facing the matrix shows irregular foldings; ruffled border. – The ruffled border is surrounded by clear zone: • Clear of organelles, rich in actin. • Creates microenvironment for bone resorption. Figure 8-6 Copyright © McGraw-Hill Companies TECHNIQUE OF PREPARATION • Ground bone: • Decalcified bone: Because of its hardness, bone cannot be sectioned routinely. Bone matrix is softened by immersion in a decalcifying solution before paraffin embedding. Decalcified bone section Figure 8-9 Copyright © McGraw-Hill Companies Histological Classification • Primary = Immature = Woven • Secondary = Mature = lamellar Lamellar Bone  Most bone in adults, compact or cancellous , is organized as lamellar bone.  Is multiple layers or lamellae of calcified matrix.  The lamellae are organized either parallel to each other (cancellous) or concentrically around a central canal (compact).  In each lamella = mainly collagen fibers type I Woven Bone • Is nonlamellar. • Is the first bone tissue to appear in embryonic development and in fracture repair. • Temporary, is replaced in adult by lamellar bone. • Random deposition of type I collagen fibers • Lower mineral content. • Easily penetrated by x-ray. • Number of osteocytes is relatively high. Bone repair Repair process involves the formation of a fibrocartilaginous callus over the break, which is subsequently replaced by a bony callus. The area surrounding the break is finally remodeled to create a strong, healed bone. Terms: • • • • • • • • • • • • • • Matrix periosteum Osteoprogenitor cells (osteogenic cells) Osteoblasts Osteocytes Lacuna Osteoclasts Canaliculi Filopodial process Haversian canal, system Osteon Volkmann canal Endosteum Osteoid

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