Bone Histology part 2.pdf

Bone Histology Part 2 Mechanical properties of bone 1. Tensile (collagen) 2. Compressive (minerals) Remember that compressive properties of bone are twice as tensile properties In other words, tensile fractures are more common than compression fractures. Homogenous Cellularity Mesench...

Bone Histology Part 2 Mechanical properties of bone 1. Tensile (collagen) 2. Compressive (minerals) Remember that compressive properties of bone are twice as tensile properties In other words, tensile fractures are more common than compression fractures. Homogenous Cellularity Mesenchymal cells osteoprogenitor cells osteoblasts (secretes osteoid) Osteocytes (in lacunae)  Homogenous Cellularity Active osteoblasts secretes matrix and appear columnar in shape. Inactive osteoblasts are flat and do not secrete matrix. Osteocytes occupy the whole lacuna. Homogenous Cellularity Osteocytes and osteoblasts are interconnected. Gap junctions are present for communication and ion flux to maintain a fine balance of calcium. Homogenous Cellularity Osteoclasts are fused macrophages that dissolve and phagocytize bone. i=they remove matrix and cellular components of the bone. Howship’s lacunae is a scooped (scalloped) edge of bone created by osteoclasts. Types of bone 1. Woven bone Characteristics: Immature or fibrous bone Can be sectioned easily b/c its not mineralized Lacunae are randomly distributed. Matrix is eosinophilic Found in developing bones, fracture sites, and bone cancer (osteosarcoma) Types of bones. Lamellar bone Characteristics: -It is a classic mature bone -Highly organized into layers containing lacunae. - Organized around osteonal (Haversian) canals that contain blood vessels. - Require special techniques to prepare histological slides such as demineralization or ground bone sections. Types of bone 2. Lamellar bone showing the organized Haversian systems (osteons). Configurations of Bone Bone configuration basically refers to the density of the bone: 1. Cancellous= spongy = trabecular bone Contains scattered bone spicules. Found in developing bones Predominant in the medullary cavity and the epiphysis. Configurations of Bone 2. Dense= compact=cortical bone Compact bone is densely arranged osteons or layers of bone. Found in the diaphysis in long bones. Organization of Lamellar Bone Lamellar bone is organized as: 1. Haversian Systems (osteons): organized osteocytes in concentric rings around a central canal. 2. non-Haversian Systems: osteons that don't surround a central canal. They are also called interstitial bone. 3. Circumferential bone: bone thickness is a result of adding layers of bone to the periosteum and endosteum by appositional growth. such a bone is called “circumferential bone” Thus, the bone made by the periosteum is called outer circumferential bone. The bone made by the endosteum is referred as inner circumferential bone. Organization of Lamellar Bone Bone Remodeling & Regulation of Serum Calcium 1. Daily calcium regulation: decrease in Ca levels will result in osteolysis where osteocytes will extract the calcium from its surrounding matrix (no structural changes will be made) 2. Long term high demand for calcium: in hypocalcemia (calcium deficiency disease). Osteoclasts will be in charge to remove entire osteons creating resorption spaces. If no calcium is available to fill in these spaces, OSTEOPOROSIS will be seen in such bones. Rickets is softening and weakening of the bone because of vitamin D deficiency which is essential to absorb calcium. Bone Remodeling & Regulation of Serum Calcium