Bone Flashcards
Function of the bone
Support, Movement, Protection, Hematopoiesis, Storage (calcium)
Bone
Specialized dynamic connective tissue with a calcified extracellular matrix (bone matrix)
Piezoelectric potential
An electrical potential generated by the bone that causes bone reabsorption because the bone is crystalized
Mechanical stress
responsible for the dynamic functions (compression/movement) and remodeling of the bone.
Type I collagen (bone matrix)
Makes up 90% of bone matrix and provides elasticity and tensile strength
Organic component of bone matrix
25% of bone matrix that consist of type I collagen, amorphous components (glycosaminoglycans, glycoproteins), and osteoid.
Osteoid
Type I collagen-rich material secreted by osteoblast. This material undergoes calcification and hardens into a new organic matrix (non-mineralized)
Osteocalcin
High affinity calcium binding protein that is secreted by osteoblast. It is a vitamin K-dependent polypeptide.
Inorganic component of bone matrix
50-70% of bone matrix that provides compressive strength to bone and mainly consist of salts of calcium phosphate.
Hydration shell
Facilitates calcium exchange with fluids in the surroundings
Bone remodeling (turnover)
The process of bone resorption and formation. It helps maintain calcium homeostasis. The turnover rate describes the period of time bone takes to remodel. Much faster in children than in adults.
Canaliculi
Small canals connecting cells in the bone matrix. They contain the dendritic processes of osteocytes that radiate from each lacuna. The canals contain a small amount of interstitial fluid that allows diffusion of metabolites between osteocytes and blood vessels.
Methods to prepare bone sections
Decalcification (flexible tissue) and grinding
Osteocyte
Terminally differentiated cells located in the lacunae. They are differentiated osteoblast that were trapped in the matrix of the bone, but ultimately maintain it. The death of these cells trigger rapid matrix resorption and activity in osteoblast and osteoclast.
Osteogenic cell
Stem cells that are the mesenchymal osteoprogenitor cells of the bone. They are located on the inner and outer linings of the bone and self renew as well as differentiate into osteoblast
Osteogenin
Bone morphogenic proteins that control the commitment of mesenchymal cells (osteogenic cells)
Osteoblast
Bone forming cells that produce the organic components of bone matrix. They are located on the matrix surface and secrete osteoids between the osteoblast layer and the existing bone layer. Their high secretory activity is due to abundant RER and Golgi. When their activity is done, they differentiate into osteocytes, form bone lining cells, or apoptosis.
Filopodia
Small microvilli located in the canaliculi (gap junctions) that allow cells to communicate between each other.
Osteoclast
Large, motile bone reabsorbing cells that break down the tissue in the bone and release minerals thus resulting in the release of calcium into the blood. They are multi-nucleated cells that are located within cavities in the matrix (Howship lacunae). Tissue is broken down through hydrolytic enzymes for proteolysis.
Howship lacunae
Also known as resorption lacunae, they are enzymaticallly etched depressions or cavities within the bone matrix that are the location of osteoclast.
Ruffled border
Bone resorption zone inside the Howship lacunae. They contain surface projections around the sealing zone that bind to the bone matrix.
Sealing (clear) zone
The membrane domain that contacts the bone during osteoclast activity. It allows the formation of a microenvironment where bone is resorbed between the matrix and osteoclast.
Proteolysis
Breakdown of proteins into smaller polypeptides or amino acids.
Periosteum
Covers the outer surface of the bone with a fibrous layer of dense connective tissue containing type I collagen, fibroblast and blood vessels. It is attached to the bone by Sharpey’s fibers and it is a point of origin for Volkmann’s canals.
Endosteum
Thin , single layer membrane that lines internal surfaces of the bone and contains osteogenic cells. It is important for bone nutrition and maintenance.
Osteogenic periosteum
Inner cellular layer that contains osteogenic cells and osteoblasts
Sharpey’s (perforating) fibers
Bundles of periosteal collagen that penetrate the bone matrix and bind the periosteum to the bone. Also are within ligaments and tendons attached to bone.