Bone Flashcards
Osteoblast originate from
osteoprogenitor cells and produce the organic components of the matrix including collagen
Osteoblasts are located exclusively at the surfaces of bone matrix as
A single layer of cuboidal cells producing a layer of collagen-rich uncalcified material called osteoid
What is calcification?
Deposition of calcium salts into the osteoid, followed by remodeling, known as ossification
Important components of osteoid include
Collagen and chondroitin sulfate, and GAG.
What causes formation of hydroxyapatite crystals
High concentration of Ca++ and PO4 ions
Communication between these structures through which nutrients derived blood vessels diffuse from cell to cell
Lacunae and canaliculi
Mechanostat
-network of dendritic processes which are part of the osteocytes
-monitors areas where loading has been increasing or decreasing and adjusts ion levels
Lack of exercise leads to
decreased bone density because of osteocyte death
Osteoclasts
Monocyte-derived white blood cells that remodel bone
Two components of bone ECM
Inorganic matter: 50% of dry bone weight is inorganic. Hydroxyapatite is the most abundant inorganic compound
-Organic matter: 90% of calcified matrix is collagen
Periosteum and endosteum connective tissue cover
external and internal surfaces of all bone
Perforating or sharpey fibers
Binds the periosteum to the bone
Periosteal blood vessels
Carry metabolites to and from bone cells
Types of bones
-Woven bones
-Lamellar bone
-Compact bone
-Cancellous bone
Woven bone (immature bone)
-Irregular and random arrangement of cells and collagen
-Developing in growing bones, hard callus of bone fractures
Lamellar bone
-Parallel bundles of collagen in thin layers
-Adult bone
-Mature bone ossified
Compact bone
80% of lamellar bone
Thick outer regions of bones
Cortical bone
Cancellous bone
20% of lamellar bone
The inner region of bones
Spongy bone, trabecular bone, medullary bone
Trabeculae serve a
supportive struts providing strength without greatly increasing the bone’s weight
Diaphysis
The cylindrical part is almost totally compact bone
Bone growth involves
Continuous resorption of older bone tissue and simultaneously laying down new bone faster than bone renewal
Bone remodeling
Conflict between osteoclasts and osteoblasts
Bone has excellent capacity of repair because
-It contains osteoprogenitor stem cells in the periosteum, endosteum, and marrow, and is vascularized
Two processes of osteogenesis
-Intramembranous ossification
-Endochoral ossfication
Intramembranous ossification
-Osteoblast differentiates directly from mesenchyme and secrete osteoid
Endochondral ossification
-A preexisting matrix of hyaline cartilage is eroded and invaded by osteoblasts which produce osteoid
Longitudinal growth in long bones is regulated by
epiphyseal plate which separates the epiphysis from the diaphysis
The primary ossification center in long bone and the secondary ossification center are separated by
Plate of cartilage called the epiphyseal plate
Appositional growth
Occurs by formation of a periosteal bone collar around the diaphysis
Epiphyseal plate
narrow regions of lower density between the denser ossification
Fracture repair
-Production of a large hematoma
-Hematoma removed by macrophages and procallus is produced
-Fibrocartilage is replaced by woven bone which forms a hard callus throughout area of fracture
-Woven then remodoles as compact and cancellous bone
Calcium are required for
activity of many enzymes and proteins
The skeleton is
90% of the calcium reservoir contained in hydroxyapatite crystals
Parathyroid hormone
Raises blood calcium levels by stimulating osteoclasts and osteocytes to resorb bone matrix and release Ca++
Calcitonin
Reduces blood calcium levels by opposing the effects of PHT
Primary bone tumor
Fairly uncommon but osteosarcoma can arise in osteoprogenitor cells
Secondary metastatic tumors
cancer cells move into bones via circulatory system from malignancies in other organs
