Bone

Question 1

Describe the matrix mineralization.

Answer 1

-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

Question 2

What are the functions of the bone?

Answer 2

1. Protect organs (brain)
2. Produce hematopoietic cells
3. Store minerals
4. Provide structure & support

Question 3

Describe the trabecular bone vs the cortical bone.

Answer 3

1. Trabecular
   -cancellous/spongy
   -large surface area
   -bone marrow
2. Cortical
   -compact
   -dense

E = epiphysis D = diaphysis M = metaphysis P = physis (growth plate) AC = cartilage

Question 4

Adult bone structure picture.

Answer 4

Question 5

Describe lamellar bone.

Answer 5

-strong, mature, forms slowly
-collagen fibers in parallel layers (lamellae) = osteoid
-organized into osteons (haversian system) in mature cortical & trabecular bone

Question 6

Describe woven bone.

Answer 6

-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

Question 7

Describe osteon.

Answer 7

-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

Question 8

Haversian system (picture)

Answer 8

Question 9

Osteon picture.

Answer 9

small holes = lacunae with osteocytes

Question 10

Femoral head picture.

Answer 10

1. C = articular cartilage
   -chondrocytes form cartilage = dark cells
   -cartilage matrix = pale
2. Tb = trabecular bone (bone spicules)
   -extends into epiphysis
   -constituted by osteocytes
3. BM = bone marrow fills the spaces between trabecular bone

Question 11

Cellular elements of bone tissue.

Question 12

Describe the structure of the trabecular bone.

Answer 12

-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

Question 13

Describe osteoblasts.

Answer 13

-produce osteoid (organic)
-initiate mineralization
-surrounded by osteoid & embedded in bone (osteocytes)

Two dots = osteocytes. Far right = osteoblasts.

Question 14

Describe osteocytes.

Answer 14

-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

Question 15

Describe osteoclasts.

Answer 15

-PTH stimulates activity
-bone resorption
-reside in shallow pits (howships lacunae)
-acid demineralization bone & enhances activity of acid hydrolases released from osteoclasts (extracellular digestion)

Question 16

Describe bone cells.

Answer 16

1. Osteoblasts = rounded, single row of cells along trabeculae
2. Osteocytes = thinner & located within lacunae
3. Osteoclasts = multinucleated along trabeculae & reabsorb bone via stimulation of cytokines secreted by osteoblasts/inflammatory cells

Question 17

Summary of cellular elements of bone.

Answer 17

Question 18

Describe the systemic hormones affecting bone.

Answer 18

1. PTH = promotes bone resorption
2. 1,25-dihydroxy Vitamin D3 = bone growth, mineralization, & stimulates bone reabsorption
3. Calcitonin = inhibits bone resorption
4. Glucocorticoids = inhibit formation & stimulate resorption
5. Estrogen = inhibits bone resorption
   insulin, growth hormone, androgens, thyroid hormone = bone metabolism

Question 19

Describe what the osteoid contains.

Answer 19

1. Type 1 collagen [main component]
2. Osteonectin = mineralization
3. Osteocalcin = Vit K
4. Proteoglycans
5. Growth factors
   *Hydroxyapatite

Question 20

Osteoid picture. [van kossa stain]

Answer 20

-unmineralized bone (osteoid) = blue
>produced by osteoblasts (ob)
-mineralized bone = black
-osteoclasts (oc) = remove mineralized bone
process of formation & resorption = coupled
>when uncoupled = disease

Question 21

Describe intramembranous ossification.

Answer 21

-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

Question 22

Describe endochondral ossification.

Answer 22

-increases length in young
-from hyaline cartilage
-precursors in physes = growth in bones (growth plate located at ends)
-hyaline cartilage precedes & is scaffold

Question 23

What are the stages of endochondral ossification?

Answer 23

1. Early cartilage (fetus)
2. Formation of primary ossification center, bony collar & periosteum
3. Vascular invasion = formation of primary marrow cavity & secondary ossification center
4. Bone at birth = enlarged primary marrow cavity & secondary marrow cavity in one epiphysis
5. Bone of child = epiphyseal plate at distal end
6. Adult bone with single marrow cavity & closed epiphyseal plate.

Question 24

Distal femur of healthy newborn calf. (Picture)

Answer 24

-metaphysis (upper)
-physis (middle)
-epiphysis (lower)

Question 25

Describe primary spongiosa.

Answer 25

-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