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40 Cards in this Set

  • Front
  • Back
What is bone?
CT specialized for strength, support, and protection.
T/F Bone is a mobilizable store for Ca and PO4 ions.
what is the main constiuent of the adult skeletal system?
What is the difference between bone tissue, and bone (the organ)
bone tissue is just that, the bone organ refers to bone tissue + marrow+ vessels+ nerves
Bone EC matrix is _______?
What is the compostition of bone?
10% of matrix is water
90-95% of organic matrix=type I collagen
what is the inorganic component of bone?
Hydroxyapetite crystals [Ca10(PO4)6(OH)2]

Composes 75% of bone weight and about 45% of the volume
where are hydroxyapetite crystals found?
gaps within collagen fibrils
what are the organic components of bone?

EC Matrix: collagen (90%); Ground Substance (GAGs and glycoproteins).
Macroscopic divisions of bone
Spongy (trabecular/cancellous): #D lattice with open spaces for blood and matrix.

Compact (dense/cortical): lacks large spaces and trabeculae, is the dense, outer portion of bone
Histological divisions of bone
Immature (primary/woven): developing skeleton, high concentration of cells and matrix has more ground substance, random arrangement.

Mature (secondary/lamellar): composed of osteons (structural unit), structurally superior, replaces woven bone throughout life.
What is an osteon?
structural unit of compact bone; "Haversian system." Cylindrical with concentric lamellae.
what are interstial lamellae?
irregularly arranged lamellae inbetween osteons
Outer and Inner Cirumferential Lamellae?
Parallel to outer/inner surfaces of the shaft of long bones.
Cementing Line?
mark the resumption of circumferential growth, does not contain collagen
Volkmann's Canals?
Nutrient Canals with blood vessels, not surrounded by concentric lamellae, run transversely/obliquely, connect haversian systems with periosteum or marrow
Outer fiberous CT layer, and inner potential osteogenic layers; surrounds bone, EXCEPT when articular cartilage is present
Cellular, potentially osteogenic layer that lines all internal surfaces of bone
Sharpey's Fibers?
Bundles of collagen that are embedded in bone so as to attach the periosteum to the bone.

Continuous with collagen bundles of a tendon, ligament, or fiberous periosteum.
What is an osteoblast?
at surface of bone, derived from osteoprogenitor cells. Responsible for matrix mineralization, with membrane receptors for hormones and cytokines.

resemble CUBOIDAL epi, with basophilic cytoplasm.

synthesize "osteiod" (unmineralized collagen with ground substance).
What does PTH do?
Secreted in response to low blood Ca levels, inhibits osteoblasts from producing more bone.
What is an osteocyte?
Cell surrounded by bone, connected to the Haversian canal via canaliculi, and one another via gap junctions.

Have surface receptors for hormones and cytokines, derived from osteoblasts.
How does bone mineralize?
Ca2+ and alkaline phosphotase vesicles are released from osteoblasts, PO4 is recruited from the matrix, and hydroxyapeptite is formed.
What are osteoprogenitor cells?
relatively undifferentiated stem cells (mesenchymal), capable of mitotic division and transformation into osteoblasts.
Where are osteoprogenitor cells found?
What are bone lining cells?
Also called "periosteal/endosteal" cells; form an attenduated layer of squamous cells on all bone surfaces.

Compoesed of quiescent osteoblasts that are connected via gap junctions.
What are osteoclasts?
Large, multinucleate cells, derived from monocytes and found in Howship's lacunae or "resorption tunnels"

Have a ruffled border, and release hydrolytic enzymes that acidify the bone surface.

Respond indirectly to PTH

Provide an acidic microenvironment to demineralized osteiod to provide optimal activity for acidic hydrolases
What does calcitonin do?
inhibits osteoclast activity in response to elevated Ca2+ levels
What is intramembranous ossification?
transformation of CT to bone via condensation of mesenchyme.
What bones are produced via endochondral ossification?
Flat bones of the face and skull, mandible, and the clavicle.
What is the progression of intramembranous ossification (i.e.steps)
1. Appearance of eosinophilic matrix with an increase in size of chondroblasts
2. Collagen runs randomly as a network of primary bone is formed.
3. Mesenchyme between spicules of bone participates in marrow formation
What is endochondral ossification?
Formation of bone from cartilage.
What bones form via endochondral ossification?
The axial skeleton that bears weight, and the appendicular skeleton (almost all, except head)
What is the progression of endochondral ossification? (i.e. steps) (**Warning: Long)
1. formation of cartilage model
2. formation of periosteal bone collar between the periosteum and the shaft of the cartilage model
3. Hypertrophy of chondrocytes (eventual death via expression of Type X collagen and alkaline phosphotase)
4. Cartilage model calcification (b/c no more diffusion of chemicals/nutrients, chondrocytes degenerate)
5. Invasion of blood vessels by periosteal bud penetration of the primary marrow cavity thru the periosteal collar, Osteoprogenitor and hematopoietic cells enter
6. Porduction of bone matrix on a calcificed cartilage backbone.
What are the regions of the epiphyseal plate?
1) Resting Cartilage: young, even cell distribution
2) Zone of Proliferation: dividing chondrocytes
3) Zone of Maturation: cells produce collagen and ground substance
4) Zone of calcification: septra of cartilage calcify and chondrocytes die
5) Zone of Ossification: osteoblasts invade
Define bone modeling, where does it take place?
Alteration in size and shape of bone

Shape the metaphysis, and plays a role is successful orthodonture
Define bone REmodeling, what are the steps?
Replacement of old, woven, or structurally inferior bone by resorption or production of new lamellar bone.

1) Clasts drill a tunnel
2) clasts disapear and blasts appear w/vessel
3) Blasts form epithelial layer lining the tunnel and begin secreting matrix. They soon become cytes
4) tunnel grows concentrically until 20-23mm in diameter
what are the steps in fracture repair? (Long)
1. Neutrophils, then macrophage arrive to the site of injury
2. Fibroblasts and capillaries proliferate
3. Osteoprogenitor cell proliferation
4. Small hyaline cartilage fragments appear in new CT
5. Dense CT and cart. form a callus to stabilize the site
6. Osteoblasts from periosteum deposit bone on the surface to from a bony sheath (intramem ossification)
7. Osteoblasts from endosteum make bone
8. Woven bone is formed by calcified cartilage (endochondral ossification)
9. Primary bone is replaced by secondary bone
10. Osteoclasts remodel the bony callus
T/F Intramembraneous and Endochondral ossification are involved in Fracture repair
T/F Bone grows both appositionally and interstitially
False...just appositional growth in bone (both in cartilage)