Osseous Tissue Structure

Concentric lamellae of osteon

Location: Osteon of compact bone Description: Concentric lamellae (layers) composed of bone matrix (ground substance) Bone matrix includes calcium hydroxyapatite and type I collagen Lamellae surround a central canal that contains blood vessels and nerves Function: Add structural support of compact bone Comment: Osteon also known as Haversian canal system Compact bone also known as dense or cortical bone

osteocyte

Location: Calcified bone matrix (extracellular matrix) Description: Osteocyte is a mature bone cell Stellate (star shaped) cell Function: Secrete substances that maintain bone matrix Detect and respond to mechanical stress on bone Comment: Latin: lacus = a lake or hollow Plural of lacuna is lacunae

Central canal of osteon

Location: Center of osteon Description: Longitudinal channel at core of concentric lamellae of osteon 20-100 µm in diameter Contains blood vessels, lymphatics, and nerves Also known as: Haversian canal Comment: Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

perforating canal

Location: Compact bone Description: Minute channel containing blood vessels and nerves Connects central canal of adjacent osteons Normally pierces oseton at right angle to central canal Also known as: Volkmann's canal

osteon (plural: ostea)

Location: Compact bone Description: Structural unit of compact bone Main components include: concentric lamellae (layers), central canal (Haversian system), osteocytes, and canaliculi Concentric lamellae of compact bone surround a central canal that contains blood vessels and nerves Osteocytes, which reside in lacunae, have processes that extend into canaliculae (a network of small canals) and contact processes of other osteocytes Function: Functional unit of compact bone Structural support of compact bone Comment: Osteon also known as Haversian canal system Compact bone also known as dense or cortical bone Other structures in compact bone, but not part of osteon, include: perforating (Volkmann) canals, circumferential lamellae, and interstitial lamellae

lacuna (plural: lacunae) of compact bone

Location: Compact bone Within matrix Description: Small space that contains cell body of osteocyte Also contains extracellular fluid

spongy bone

Location: Inner core of bones Description: System of plates and trabeculae separated by spaces that contain bone marrow Composed of mineralized, interstital substance (bone matrix) Spongy bone always surrounded by compact bone Function: Plate and trabecular structure (rather than solid) very important in keeping bone light-weight but strong Site for hematopoiesis and fat storage Also known as: Cancellous bone Comment: Trabeculae form along stress vectors for a bone

lamella (plural: lamellae) in osteon of compact bone

Location: Osteon Description: Thin layer of bone Concentric lamellae around central (Haversian) canal comprise osteon of compact bone Function: Deposit bone matrix in layers to form osteon Comment: Latin: lamina = plate Four lamellar systems in compact bone: (1) outer circumferential lamellae, located just deep to periosteum; (2) inner circumferential lamellae, which surround marrow cavity; (3) concentric lamellae that form osteons; and (4) interstitial lamellae, which are remnants of osteons

periosteum

Location: Outer surface of most bone Description: Fibrous layer of condensed connective tissue covering bone Bound to underlying bone by collagen fibers Contains numerous osteoprogenitor cells Does not cover articular surfaces or attachment sites of tendons and ligaments Comment: During bone growth or repair osteoprogenitor cells differentiate into osteoblasts Essential to bone nutrition, growth, and repair

Compact bone

Location: Outer surfaces of bones Description: Composed of mineralized interstital substance (bone matrix) Osteon is basic structural unit: concentric layers of bone matrix that surround a central canal Contains lacunae (microscopic, uniformly spaced cavities) Lacunae contain osteocytes (bone cells) Lacunae interconnected by canaliculi (tubular passages) Comment: In flat bones of skull, compact bone forms plates on the inner and outer surfaces; plates are separated by spongy bone called diploe

red bone marrow

Location: Spongy bone Between trabeculae Description: Spaces between trabeculae that contains marrow Red marrow dominated by maturing erythrocytes; found in ends (epiphyses and metaphyses) of long bones Yellow marrow dominated by adipocytes; found in shafts (diaphysis) of long bones and in flat bones (e.g., hip bones, skull, vertebrae, and scapulae) Function: Red marrow (or active marrow): hematopoiesis (i.e., production of blood cells) Yellow marrow (or inactive marrow): fat storage Comment: At birth, all marrow is red; with age, red marrow converted to yellow marrow Spongy bone also known as cancellous or trabecular bone

trabecula (plural: trabeculae) of spongy bone

Location: Spongy bone Description: Network of fine, irregular plates (lamellae) of bone Bony plates are separated by communicating spaces Function: Delineates marrow cavities Distributes stresses and forces Comment: Spongy bone also known as cancellous or trabecular bone Latin: trabs = beam (plural, trabeculae)

Canaliculus (plural: canaliculi)

Location:Matrix of compact bone Description:Minute channels extending from lacuna Connects adjacent lacunae Contains fine cytoplasmic processes of osteocytes and extracellular fluid Comment: Pathway for diffusion of nutrients, gases, and metabolites for osteocyte

nutrient foramen

Opening through compact bone, allows passage of artery into medullary cavity

dense regular connective tissue

collagen fibers oriented in the same direction found in tendons and ligaments

dense irregular connective tissue

collagen fibers woven in multiple directions found in periosteum, deeper portion of dermis skin, capsules and around viscera such as kidney, liver, spleen; fibrous sheaths around cartilages and bone