Study Guide - Connective Tissue - Bone.pdf

Study Guide Connective Tissue - Bone A. Describe the general structure of bone 1. Cortical bone (also known as Compact Bone) i. Tough outer layer ii. Majority of bone in the body iii. Cover...

Study Guide Connective Tissue - Bone A. Describe the general structure of bone 1. Cortical bone (also known as Compact Bone) i. Tough outer layer ii. Majority of bone in the body iii. Covered by periosteum on superficial surface (a) This contains blood vessels 2. Cancellous Bone (also known as Trabecular Bone or Spongy Bone) i. Spongy, mesh plates ii. In contact with bone marrow B. Describe the cellular and non-cellular components of bone 1. Cellular Component i. Osteoblasts (a) Immature bone cells (b) Secrete extra-cellular matrix to give bone its material properties (c) Eventually can: (a) Become osteocytes (see below) (b) Become bone lining cells (c) Die via apoptosis ii. Osteocytes (a) Mature bone cells (b) Maintain extracellular matrix (a) Response to mechanical loading (b) Response to hormones iii. Osteoclasts (a) Break down extracellular matrix (a) Releases minerals into the blood stream (b) Provides space for osteoblasts to secrete new extracellular matrix iv. Bone Lining Cells 2. Non-cellular Component (extracellular matrix, secreted by osteoblasts) i. Non-mineralized (a) Osteoid is the main non-mineralized component (a) Collagen is main protein in osteoid ii. Mineralized (a) Hydroxyapatite is main mineralized component C. Differentiate between the two classifications of bone based on the tissue’s maturity level 1. Immature bone = woven bone i. Also known as “primary bone” ii. Found during fracture repair process (and also in fetal growth) iii. Weaker than mature bone (a) Irregular collagen structure  (b) Less mineral content in osteoid 2. Mature bone = lamellar bone i. Also known as “secondary bone” ii. Forms in remodeling process (i.e. woven bone has stressors placed upon it, and remodels) iii. Stronger than woven bone (a) Osteon structure of concentric rings (a) Adapted based on stressors placed upon it (b) Osteocytes houses in lacunae (c) Haversian canals contain blood vessels and lymphatic vessels (d) Volkmann’s canals connect osteons together (b) More mineral content in osteoid 3. Both, cortical bone and cancellous bone can exist in immature forms D. Describe the process of fracture repair 1. Occurs by regeneration and remodeling i. No scar ii. Return to optimal functioning possible 2. Duration is dependent upon multiple factors i. Fracture site ii. Type iii. Treatment iv. Soft tissue involvement v. Individual factors, including (a) Age (b) Immunocompetency (c) Nutritional status 3. Phases of healing i. Internal bleeding delivers cells to the site of injury, which secrete a number of growth factors, and eventually results in clotting (a) Fibroblasts (b) Platelets (c) Osteoprogenitor cells (a) Bone precursor cells (b) Can become osteoblasts, osteoclasts, etc. (d) Mesenchymal cells (a) Can become (i) Fibroblasts (ii) Chondroblasts (produce cartilage) (iii) Osteoprogenitor cells (e) Inflammatory cells ii. Hematoma forms (a) Lasts about a week iii. Inflammation occurs (a) Granulation tissue forms (a) Fibrosis  (b) Neovascularization (new blood vessel formation) iv. Soft callus forms after about 2 weeks (a) Osteoclasts clear necrotic bone (b) Periosteum and endosteum regenerate (a) Different into (i) Hyaline cartilage (soft callus) (ii) Bony spicules (hard callus) (c) Soft callus formation immobilizes fracture site v. Hard callus begins to develop (1+ week after soft callus) (a) Fibrocartilage (b) Endochondral ossification occurs (a) Transformation of cartilage to bone vi. Remodeling occurs (a) Months to years (b) Woven bone replaced with lamellar bone (c) Excessive callus is resorbed (d) Bone remodels in relation to mechanical stresses placed upon it (Wolff’s law!)