Flashcards in Bones Deck (56):
The structure of individual bones is designed to provide what?
maximum resistance to mechanical stress while maintaining the least body mass
What is bone?
specialized connective tissue consisting of cells embedded within a gel-like substance that becomes mineralized
- marked rigidity and strength while retaining a degree of elasticity
- both a tissue and an organ
what is an organ?
a group of tissues that perform a specific function or group of functions
What are the functions of bones?
-support and protection
- shape and movement
- source of calcium reserve (99%) and storage of other inorganic ions
- active participation in the maintenance of calcium homeostasis in the body
How do bones accommodate changes related to mechanical stresses and demands on calcium homeostasis?
by being in a dynamic state of growth and resorption throughout their life
What is the osteoid?
the matrix of organic extracellular material that primarily contains glycoproteins and colagen fibers
What happens to the osteoid in order to form bone?
rapidly undergoes mineralization by deposition of inorganic salts, mainly calcium hydroxyapatite (CHAP) crystals, to form bone
The variety of growth factors in the matrix probably play an important role in what?
- bone development
What is the general consistency of substances in the bone? (%)
22% Organic matrix
69% Inorganic matrix
What is the primary component of the organic matrix? What feature is it responsible for?
collagen type I - responsible for the tensile strength
What is the inorganic matrix of bone mainly composed of?
hydroxyapatite crystals deposited within collagen fibrils to enhance tensile strength
What are the main minerals in bone?
Calcium phosphate (85%)
Calcium carbonate (10%)
Na, Mg, Fe (>5%)
What are collagen fibers produced by? What do they provide?
produced by osteoblasts and provide framework and necessary tensile strength
What do the proteoglycans of the bone that are embeded in collagen fibers do?
serve as a carrier for minerals
How does the bone matrix harden (becomes mineralized)?
by deposition mainly of hydroxyapatite
What are the envelopes of bone?
What is the Periosteum?
a fibrous connective tissue layer that covers outer/external surfaces of bones
- a site of insertion of muscles, tendons and ligaments
What is the Endosteum?
the inner delicate connective tissue surface of the bone
- lines the trabeculae of spongey bone
What cells are contained in both the periosteum and endosteum?
osteogenic stem cells
What are the functions of osteogenic stem cells?
- continuous remodeling
- repair of bone fractures
What are the characteristics of bone lining cells?
- flat, elongated cells
- generally inactive
- cover surfaces of inactive bone
- precursor cells to osteoblasts
What are the characteristics of osteoblasts?
- matrix formation
- secrete type I collagen
- regulate mineralization
- positioned external to osteoid matrix
- differentiate to become osteocytes
What are the characteristics of osteocytes?
- originate from osteoblasts
- maintain bone matrix
- occupy lacunae
- extend filopodia through canaliculi
- form gap junctions with neighboring cells
What are the characteristics of osteoclasts?
- digest bone
- large multinucleated cells
- exhibit ruffled border and clear zone
- exhibit polarity with nuclei away from bone surface
- originate from pluripotent stem cells of bone marrow
What are the types of bone based on maturity
woven bone and lamellar bone
-immature bone present during fetal development and in early stages of bone repair
-collagen fibers make a crisscross woven pattern
-mature bone, collagen fibers arranged in parallel pattern
what are the two ways in which fetal bones form
intramembranous ossification and endochondral ossificationi
-occurs within condensed mesenchymal tissue; ie. flat bones of the skull
-also occurs at periosteal surfaces post-natally, and thus causes growth of width in long bones
-occurs in most skeletal bones; allows length growth in long bones
-bones develop from hyaline cartilage by replacing it with ossesous tissues via ossification centers
-ossification occurs at oss. centers of immature bone and growth plates/epiphyseal plates of developing bone
-once the growth plate closes no further length can be achieved
Cartilage or bone: this tissue is avascular, cells are separate, and there are no nerves in the matrix
cartilage or bone: poor healing potential, and appositional and interstitial growth
osteoblasts originate from
osteoblasts are found exclusively
on surface of bones
synthesis and secretion of collagen and osteoid: the organic components of extracellular matrix of bone
-osteoblasts are also cuboidal
-an osteoblast that has had its surrounding osteoids mineralize and encase them
-mature bone cells enclosed in bone matrix within lacunae
how do osteocytes maintain contact with adjacent cells and transfer nutrients?
-via filipodia: cytoplasmic branching processes connecting osteocytes via canaliculi (small tunnels)
-nutrients are transfered via gap junctions
true or false: osteocytes undergo mitosis
-synthesize and reabsorb their matrix to maintain homeostasis of Ca++
-large multinucleated cells, closely related to macrophages
osteoclasts originate from
bone marrow, from monocytes
osteolysis, the breakdown of bone matrix to maintain Ca++ homeostasis and remodel matrix in response to growth or changes in mechanical strength
-when activated while within contact with bone surface they release enzymes to decalcify bone
lamellar bone is composed of
successive layers of osteocytes and bone matrix
lamellar bone may be formed as either
compact bone (solid) or cancellous bone (spongy mass)
haversian system arrangement of osteocytes
-form concentrically around blood vessels, nerves, and osteogentic/osteoclastic cells
-vessels, etc lie within harvesian canal
concentric lamellae contain
osteocytes surrounded by mineralized bone, each connected by canaliculi
harvesian canals are interconnected, and connected to endosteum and periosteum via
Volkmann's canals, which run at right angles to harversian canals
what is the functional unit of mature bone
osteon: concentric layers of osteocytes and mineralized bone surrounding a harvesian canal
2 factors that influence formation and reabsorption of bone
parathyroid hormone (PTH) and vitamin D
parathyroid hormone function
increases development and activity of osteoblasts and osteoclasts
vitamin D function
increases recruitment of osteoclasts, and mineralization of bone matrix
increased osteoclastic activity, results in osteolysis
-serum Ca++ increases, and estrogen inhibits bone resorption
-stimulates bone formation via inhibition of osteoclastic action
-serum Ca++ decreases, and osteoblsts are stimulated to form osteoids
cavity between two movable bones
-bone surfaces are covered in Articular cartilage
-synovial membrane is highly vascularized, and lined with epitheloid cells that secrete hyaluronic acid to phagocytize debris