histology lec (midterm)

• ECM - component of bone impedes the distribution of nutrients

  and oxygen to osteocytes
• compact bone - characterized by the presence of osteons
• osteocytic processes - in healthy bone, canaliculi are likely to contain
• endosteum - a thin layer of active and inactive

  osteoblasts, which lines all the internal surfaces within bone; osteoblasts here are also required for bone growth
• spongy bone - composed of trabeculae that form an interconnected network
• bone marrow cavity - contains red blood cells and fatty tissue
• zone of ossification - “zone” of endochondral ossification in the growing femur of

  an adolescent is the farthest from that bone’s secondary ossification center
• collagen is mainly type II - typical feature of elastic cartilage?
• territorial matrix - area in cartilage is relatively collagen-poor and proteoglycan-rich?
• what distinguishes cartilage from most other connective tissues? it lacks blood vessels.
• articular cartilage covers the articular surfaces of synovial joints
• how does articular cartilage differ from most other hyaline cartilage? it lacks a perichondrium.
• step occurs first in chondrogenesis? formation of mesenchymal condensations
• all forms of cartilage form from?

  embryonic mesenchyme
• osteoblast - growing cells which synthesize and secrete the organic components of the matrix
• secrete components of the initial matrix called

  osteoid, that allow matrix mineralization to occur
• osteiod - a layer of unique collagen material between the

  osteoblast layer and preexisting bone surface
• osteocytes - maintain the calcified matrix and detect

  mechanical stresses on bone and maintain communication with adjacent cells via gap junctions at the ends of their processes
• first bone tissue to appear in embryonic

  development and fracture repair and has type I collagen

  fibers and has lower mineral content

  woven bone
• lamellae organized concentrically around

  small central canals containing blood

  vessels and nerves (osteon or haversian

  system)
• refers to the complex of concentric

  lamellae surrounding a central canal that

  contains small blood vessels, nerves, and

  endosteum?

  osteon/harversian system
• Perforating canals/ Volkmann canals - allow canals to communicate with one another; have few concentric lamellae
• Interstitial lamellae - numerous irregularly shaped groups of parallel lamellae from remaining osteons

  partially destroyed by osteoclasts during

  growth and remodeling of bone
• intramembranous ossification - by which most flat bones begin to form, takes place within condensed sheets (“membranes”) of embryonic mesenchymal tissue.
• endochondrial ossification - ossification takes place within hyaline cartilage and type of ossification that forms most bones of the body
• interstitial growth – important in

  increasing length of lone bones
• appositional growth – important postnatal development
• articular cartilage – within the joints

  between long bones which normally persists

  through adult life
• epiphyseal cartilage - which connects each

  epiphysis to the diaphysis and allows longitudinal bone growth
• zone of reserve (or resting) cartilage is composed

  of typical hyaline cartilage.
• chondrocytes undergo mitosis and appear

  stacked within elongated lacunae - zone of proliferation
• most mature chondrocytes in these lacunae

  swell up, compress the matrix, and undergo apoptosis - zone of hypertrophy
• chondrocytes about to undergo apoptosis

  release matrix vesicles and osteocalcin to

  begin matrix calcification by the formation

  of hydroxyapatite crystals. - zone of calcified cartilage
• bone tissue first appears and woven bone is laid down initially by osteoblasts and remodeled into lamellae

  bone - zone of ossification
• lamellae and osteons - temporary structures and

  are replaced and rebuilt continuously in a process

  of bone remodeling by which bones change size

  and shape according to changes in mechanical

  stress.
• Soft, fibrocartilage-like callus – initial bone repair structure formed after fracture or other injury which involves the activation of periosteal fibroblasts.
• Hard callus of woven bone – replaces the

  soft callus that is soon remodeled to

  produce stronger lamellar bone
• calcium - a key ion for all cells, is stored in bone

  when dietary calcium is adequate and mobilized

  from bone when dietary calcium is deficient.
• Parathyroid hormone (PTH) - indirectly stimulates

  osteoclasts to elevate levels of calcium in blood

  Calcitonin - inhibit osteoclast activity, lowering

  blood calcium levels.
• perichondrium - essential for the growth and maintenance of cartilage, consists largely of collagen type I

  fibers and fibroblasts,