bone

bone is

highly vascular

3 types of cells of bones

osteoblasts, osteocytes, osteoclasts

osteoblasts

cover outer & inner surfaces of bone, not located within lacunae

osteocytes

derived from osteoblasts, located within lacunae

osteocytes extend

through microscopic canals within the matrix called canaliculi

canaliculi purposes

intercellular communication, nutrient and waste flow

osteoclasts

are multinucleated giant cells

osteoclasts produce

lysosomal enzymes that digest collagenous matrix, organic acids that dissolve mineralized matrix

osteoclasts digest

bone cavity between cell and matrix called erosion lacunae

osteoid

matrix of bone

organic components of the matrix

fibers (type 1) and ground substance

organic components accounts for

tensile strength of bone, resisting breakage under tension

inorganic component of the matrix

hydroxyapatite crystals

inorganic component accounts for

the compressive strength of bone

bone formation occurs in two steps

matrix secretion by osteoblasts followed by, and mineralization of the matrix into bone

types of bone (microscopic)

woven bone, lamellar

woven bone

immature bone, no haversian systems

woven bones are formed

rapidly so cells and collagen fibers are arranged irregularly

woven bones found in

developing bone

woven bone is

replaced by lamellar bone

lamellar bone

mature bone, has haversian systems

lamellar is formed

slowly by remodeling woven bone precursor

lamellar cells and collagen fibers

are arranged in organized layers (lamellae)

types of bone, gross

compact/cortical, cancellous/trabecular/spongy

compact/cortical bones

dense shell of outer bone that microscopically may be woven bone, lamellar bone, or mixed

cancellous bone

small spicules of inner bone that microscopically may be woven bone, lamellar bone or mixed

haversian system

aka osteon

haversian system, structural unit of mature bone

consists of concentric layers of lamellae around a central canal, forms a tubular unit that runs the length of the bone

central canal

center of osteon

central canal contains

blood & lymphatic vessels and nerve fibers

lamellae has

concentric layers of bone matrix, the direction of the collagen fibers alternates in each layer

osteocytes

reside in lacunae located at regular intervals between the lamellae

lacunae

houses the osteocyte

canaliculi

connect adjacent lacunae and enable cell-cell communication between osteocytes and nutrient and waste flow

perforating canals

act to interconnect longitudinally arranged central canals with each other and the medullary cavity of the bone

interstitial lamellae

orphan fragments of partially-degraded osteons, no central canals

inner circumferential lamellae

not part of the osteons, arranged in circular pattern around marrow cavity

inner circumferential lamellae is

covered by endosteum

outer circumferential lamellae

not part of osteons, smooths the outer surface of the bone

outer circumferential lamellae is covered

by the periosteum

3 type of CT coverings of bone

endosteum, periosteum, perforating fibers

endosteum

inner CT lining of bone

endosteum covers

all inner surfaces and surrounds blood vessels

endosteum is made up of

fine, loosely-organized collagen fibers

periosteum

outer CT lining of bone

periosteum is

highly vascularized and innervated, source of pain

2 components of periosteum

fibrous layer and cellular layer

fibrous layer (periosteum)

composed of dense regular to irregular CT, acts as a capsule

predominant cell type of fibrous layer

fibroblast

cellular layer (periosteum)

btwn the fibrous layer and the cortical bone

cellular layer is

highly cellular, filled with osteoprogenitor cells

perforating fibers