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.
Volkmann’s canals
Perforating canals that zig-zag through lamellar bone. They are carrying blood vessels to the bone marrow and into the circulatory system.
Chondroprogenitor
Mesenchymal cells that differentiate via a cartilage pathway (Chondroprogenitor -> Chondroblast -> Chondrocyte). They lack blood vessels.
Bone proper
It includes woven bone and lamellar bone. It is an organization of collagen fibers in matrix.
Woven bone
Primary, immature bone that is characterized by the random disposition of type I collagen fibrils. It appears in embryonic development and fracture repair but is only temporary and is replaced by lamellar bone in adults.
Lamellar bone
Secondary, mature bone that is an organization of heavily calcified, parallel type I collagen fibers (lamellae). It can either be compact or cancellous and is a result of remolding woven bone.
Compact bone
Dense, cortical bone that represents 80% of the total bone mass. It is located on the outer region of the bone and contains parallel lamellae and densely packed osteons.
Cancellous bone
Spongy bone with numerous interconnecting cavities. It makes up 20% of the total bone mass and is located on the inner regions of bones, adjacent to marrow cavities.
Trabeculae
Network of irregular lamellae, also called spicules
Anastomose
Fusion of trabeculae trapping blood and lymphatic vessels inside canals
Haversian system (Osteon)
Cylindrical columns of 4-15 concentric lamellae surrounding the Haversian canal. It is constantly being remodeled.
Epiphyses
Bulbous ends of long bones that are composed of cancellous bone covered by a thin layer of compact bone.
Diaphysis
Cylindrical part of long bones that is almost all compact bone, but has a thin region of cancellous bone on the inner surface around the central marrow cavity.
Diploë
Thick layer of cancellous bone in the skull that separates the two layers of compact bone (plates) to form the calvaria (skullcap)
Alkaline phosphatase
Promotes accumulation of inorganic phosphate in the osteoid
Osteonectin
High affinity calcium binding glycoprotein. Similar to osetocalcin.
Osteoporosis
Bone resorption is greater than bone deposition which leads to a loss of bone mass. Common in elderly people.
Osteopetrosis
Bone deposition is greater than bone resorption which leads to an excess in bone mass. Due to abnormal osteoclast.
Vitamin C deficiency
Can result in altered collagen formation, fragile bone, fractures, and scurvy.
Vitamin D deficiency
Impaired intestinal absorption of calcium.
Vitamin D excess
Abnormal calcification of soft tissues, toxic
Vitamin A deficiency
Results in skeletal deformities, slow bone growth, or premature epiphyseal closure
Vitamin A excess
Slow cartilage growth and accelerated ossification
Ossification canter
Area where osteoprogenitor cells arise, proliferate, and form incomplete layers of osteoblasts around a network of developing capillaries.
Primary ossification center
Located in the diaphysis, it is the beginning of the formation of primary bone and bone marrow through expansion and remodeling.
Secondary ossification center
Located in the epiphysis. Same process as the primary ossification center (invasion by epiphyseal artery, primary bone and marrow formation). Origin of the epiphyseal growth plate.
Epiphyseal growth plate
Connects each epiphysis to the diaphysis. Allows for longitudinal growth through the zones of epiphyseal cartilage. Eliminated upon completion of bone growth in adulthood.
5 Zones of epiphyseal cartilage
- Zone of reserve (resting) - hyaline tissue
- Proliferative zone - cell division by interstitial growth
- Zone of maturing - hypertrophy
- Zone of calcified cartilage - matrix calcification
- Zone of ossification - endochondral ossification
Hypertrophy
Swelling up of chondrocyte cells. This process causes the cells to die and leave empty spaces within the calcified matrix for periosteal buds to fill during endochondral ossification.
Bone repair
Endochondral ossification used to repair bone. A problem occurs (fracture/interruption of blood supply), then osteoprogenitor cells become chondrogenic. Cartilage forms (4 days), blood vessels reform, and then primary and secondary bone reforms (> 2 weeks). Mechanical stress and muscular activity necessary to restore bone shape.
Synarthrose joint
Joints that permit little to no movement. Can be fibrous or cartilaginous.
Synostoses
Immobolized, fused bone (skull)
Synchondrose
Bones joined by hyaline cartilage (rib/sternum)
Symphysis
Bones joined by fibrocartilage (pubic symphysis, intervertebral discs)
Diarthrose joint
Joints that allow movement between long bones. Contain articular cartilage, synovial fluid, and capsules. They are reinforced by ligaments and stabilized by muscles and tendons.
Synovial fluid
Viscous fluid that lubricates the joint, reduces friction on internal surfaces, and supplies nutrients & oxygen to articular cartilage
Type A cells
Macrophage-like synovial cells. Removes debris from the synovial fluid.
Type B cells
Fibroblastic synovial cells. Forms the synovial fluid
Rheumatoid Arthritis
Autoimmune disease causing chronic inflammation of the joints and tissue around the joints
Parathyroid hormone (PH)
Raises low blood calcium levels by stimulating osteoclasts and osteocytes to resorb bone matrix and release Ca2+
Calcitonin
Reduces elevated blood calcium levels. Directly targets osteoclasts to slow matrix resorption and bone turnover. Produced in thyroid gland.
Haversian canal
Contains blood, lymphatic vessels, and nerves. The central canal is the source of nutrients and oxygen.
