Histology - Bone

osteoblasts

cover outer and inner surfaces of bone, when inactive called bone lining cells, not located within lacunae

osteocytes

derived from osteoblasts, are located within lacunae and are embedded in the matrix

canaliculi

cytoplasmic processes of osteocytes within the matrix that aid in intercellular communication and nutrient/waste flow

osteocytes

multinucleated giant cells that digest collagenous matrix and dissolves mineralized matrix

osteoid

matrix of bone

organic components of bone

type 1 collagen and ground substance that contains GAGs and glycoproteins like condroitin sulfate and dermatin sulfate , accounts for TENSILE strength

inorganic components of bone

hydroxyapatite crystals, accounts for COMPRESSIVE strength of bone

woven bone

immature bone, no haversian systems, formed rapidly so cells and fibers are arranged irregularly, found in developing bone, replaced by lamellar bone

lamellar bone

mature bone, has haversian systems, formed slowly by remodeling woven bone, most of adult skeleton, cells and fibers are arranged in organized layers called lamellae

compact/cortical bone

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

cancellous/trabecular/spongy bone

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

haversian system

osteon, structural unit of mature bone that consists of concentric layers around a central canal

central canal

at center of osteon, contains blood, lymphatic vessels, and nerve fibers

lamellae

concentric layers of bone matrix

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/waste flow

perforating canals

volkman’s 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

arranged in a circular pattern around marrow cavity, smooths inner surface of bone, covered by endosteum

outer circumferential lamellae

smooths the outer surface of the bone, covered by periosteum

endosteum

inner CT lining of bone, covers all inner surfaces and surrounds blood vessels, fine and loosely organized collagen fibers, hard to id

periosteum

outer CT lining of bone, highly vascularized and innervated, has two subcomponents called the fibrous layer and the cellular layer

fibrous layer of periosteum

composed of dense regular to irregular CT, outer layer that acts as capsule, predominant cell type is fibroblast

cellular layer of periosteum

between the fibrous layer and corticaal bone, highly cellular and filled with osteoprogenitor cells

perforating fibers

sharpey’s fibers, bundles of type 1 collagen fibers from the outer fibrous layer of the periosteum that embed into the outer circumferential layer of the bone, anchors periosteum to bone, and is how tendons and ligaments anchor to bone

articular cartilage

not covered by a perichondrium so that diffusion can occur to provide nutrients and exchange gases with chondrocytes

subchondral bone

bone immediately beneath the articular cartilage, is initially compact bone but transitions to trabecular/cancellous bone

joint capsule

has two parts, inner synovial membrane and the outer fibrous collagenous layer

inner synovial membrane

specialized epithelium that secretes synovial fluid, an ultrafiltrate of blood with high hyaluronic acid content, forming viscous fluid that fills the joint space and lubricates and nourishes the articular cartilage