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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
- modeling
- remodeling


What is the general consistency of substances in the bone? (%)

9% water
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?

- Periosteum
- Endosteum


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?

- growth
- 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


woven bone

-immature bone present during fetal development and in early stages of bone repair
-collagen fibers make a crisscross woven pattern


lamellar bone

-mature bone, collagen fibers arranged in parallel pattern


what are the two ways in which fetal bones form

intramembranous ossification and endochondral ossificationi


intramembranous ossification

-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


endochondral ossfication

-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