Bone Flashcards
Describe the matrix mineralization.
-osteonectin & osteocalcin = absorb to type I collagen & bind Ca
-osteoid is not mineralized immediately after despoliation (delay 5-10 days)
>failure to mineralize bone = rickets = osteomalacia
>soft bones & fractures
What are the functions of the bone?
- Protect organs (brain)
- Produce hematopoietic cells
- Store minerals
- Provide structure & support
Describe the trabecular bone vs the cortical bone.
- Trabecular
-cancellous/spongy
-large surface area
-bone marrow - Cortical
-compact
-dense
Adult bone structure picture.
Describe lamellar bone.
-strong, mature, forms slowly
-collagen fibers in parallel layers (lamellae) = osteoid
-organized into osteons (haversian system) in mature cortical & trabecular bone
Describe woven bone.
-weak, immature, made quickly
-disorganized collagen fibers
-at sites of rapid bone formation (ex. Fracture repair, inflammation, neoplasia)
EX: periosteal new or reactive bone
woven bone can be remodeled into lamellar bone
Describe osteon.
-functional unit of lamellar bone
-located in cortex, trabeculae of bones (haversian) & in interstitial bone between circles of bone
-Haversian canal at center of each osteon
-volkmans canals are running in bone connecting haversian (central) canals blue line
Haversian system (picture)
Osteon picture.
small holes = lacunae with osteocytes
Femoral head picture.
- C = articular cartilage
-chondrocytes form cartilage = dark cells
-cartilage matrix = pale - Tb = trabecular bone (bone spicules)
-extends into epiphysis
-constituted by osteocytes - BM = bone marrow fills the spaces between trabecular bone
Cellular elements of bone tissue.
Describe the structure of the trabecular bone.
-osteoblasts along bone spicules = produce osteoid (a pivotal protein matrix)
-osteoblasts trapped in osteoid = become osteocytes
-osteocytes in bone lacunae = reabsorb bone (osteocytic/osteolysis) during remodeling, bone injury, or in response to hypocalcemic states
-osteoclasts = multinucleated phagocytic cells (responsible for bone resorption = osteoclastic/osteolysis)
-Howships lacunae = create small concavities in bone spicules
Describe osteoblasts.
-produce osteoid (organic)
-initiate mineralization
-surrounded by osteoid & embedded in bone (osteocytes)
Describe osteocytes.
-most abundant
-located in lacunae surrounded by mineralization matrix (long filipods increase cell area)
-regulate exchange of Ca
-fluid & ECF under influence of parathyroid hormone
Describe osteoclasts.
-PTH stimulates activity
-bone resorption
-reside in shallow pits (howships lacunae)
-acid demineralization bone & enhances activity of acid hydrolases released from osteoclasts (extracellular digestion)
Describe bone cells.
- Osteoblasts = rounded, single row of cells along trabeculae
- Osteocytes = thinner & located within lacunae
- Osteoclasts = multinucleated along trabeculae & reabsorb bone via stimulation of cytokines secreted by osteoblasts/inflammatory cells
Summary of cellular elements of bone.
Osteoid picture. [van kossa stain]
-unmineralized bone (osteoid) = blue
>produced by osteoblasts (ob)
-mineralized bone = black
-osteoclasts (oc) = remove mineralized bone
process of formation & resorption = coupled
>when uncoupled = disease
Describe intramembranous ossification.
-increase width in adult
-from mesenchymal tissue in periosteum at sides
-in flat bones of skull & pelvis
-on all periosteal surfaces throughout life
-growth of bones
>no cartilage needed first
Describe endochondral ossification.
-increases length in young
-from hyaline cartilage
-precursors in physes = growth in bones (growth plate located at ends)
-hyaline cartilage precedes & is scaffold
What are the stages of endochondral ossification?
- Early cartilage (fetus)
- Formation of primary ossification center, bony collar & periosteum
- Vascular invasion = formation of primary marrow cavity & secondary ossification center
- Bone at birth = enlarged primary marrow cavity & secondary marrow cavity in one epiphysis
- Bone of child = epiphyseal plate at distal end
- Adult bone with single marrow cavity & closed epiphyseal plate.
Distal femur of healthy newborn calf. (Picture)
-metaphysis (upper)
-physis (middle)
-epiphysis (lower)
Describe primary spongiosa.
-Endochondral bone formation is preceded by hyaline cartilage
-It occurs in physes when cartilage differentiates, matures, mineralizes, dies & is scaffold that osteoblasts reside on
-Osteoblasts produce osteoid on top of the spicules of dark blue cartilage (arrow) = Primary Spongiosa
-Osteoid is pink (unmineralized & soft)
-Cartilage is blue
-Bone produced in the primary spongiosa is remodeled & mineralized into mature lamellar bone
