Bone

Question 1

Describe osteoclasts

Answer 1

very large and multiple nuclei and motile. essential for matrix reabsorption during bone growth and remodeling. they originate from monocytes. they require the RANKL to differentiate.

Question 2

How do osteoclasts remodel bone?

Answer 2

proton pumps acidify and promote dissolution of the hydroxyapatite and release proteinases and other hydrolytic enzymes from lysosome related secretory vesicles.

Question 3

how are osteoclasts regulated?

Answer 3

controlled by signaling factors from other bone cells. they are activated by parathyroid hormone and produce RANKL and other factors that regulate their activity.

Question 4

describe osteoblasts

Answer 4

originate from mesenchymal stem cells, they produce components of bone matrix including collagen fibers, proteoglycans and matricellular glycoproteins like osteonectin.

Question 5

osteoblast activity

Answer 5

they secrete a collagen rich material called osteoid between the osteoblast layer and the preexisting bone surface. they process of growth is completed by deposition of calcium salts into the matrix.

Question 6

mineralization of osteoblasts

Answer 6

osteoblasts release matrix vesicles, the released matrix vesicles are with collagen fibers, there is mineralization around the vesicles and then hydroxyapatite crystals form and begin calcification. eventually this produces calcified materials embedding the collagen fibers and proteoglycans

Question 7

describe osteocytes

Answer 7

osteoblasts become surrounded by the material they secrete and then they become osteocytes enclosed within the lacunae throughout the mineralized matrix.

Question 8

Mineralization of bone from osteoblasts

Answer 8

1. Osteocalcin – binds Ca²⁺ increase local Ca²⁺
2. Matrix vesicles of alkaline phosphatase – increases PO₄⁻ locally 3. Ca and PO form calcified nanocrystal
3. Nanocrystals merge and grow, forming hydroxyapatite crystals → merge into solid bone matrix

Question 9

Composition of the bone matrix

Answer 9

90% type 1 collagen, small proteoglycans, multiadhesive glycoproteins such as osteonectin which is a calcium binding protein

Question 10

Periosteum

Answer 10

Two layers, inner stem cells, outer dense CT

mostly cellular, includes osteoblasts, bone lining cells, and mesenchymal cells (osteoprotenitor cells). potential to proliferate extensively producing osteoblasts and osteoprogenitor cells. play major role.

Question 11

Endosteum

Answer 11

covers small trabeculae of matrix and contains osteoprogenitor cells, osteoblasts, and bone lining cells with a sparse delicate mix of collagen fibers

Question 12

Epiphyses

Answer 12

in long bones; the bulbous ends. composed of cancellous bone covered by a thin layer of cortical bone.

Question 13

Diaphysis

Answer 13

the cylindrical part, totally dense compact bone with a thin region of cancellous bone on the inner surface around the central marrow cavity.

Question 14

Where are osteogenic stem cells?

Answer 14

periosteum and endostieum

Question 15

Intramembranous ossification

Answer 15

osteoblasts differentiate from mesenchyme and begin secreting osteoid. (most bones of the skull, jaws, scapula and clavicle are formed embryonically by intramembranous ossification.

Question 16

process of intramembranous ossification

Answer 16

1) bone formation begins in ossification centers
2) osteoprogenitor cells arise, proliferate, adn form incomplete layers of osteoblasts around a network of developing capillaries
3) osteoid secreted by the osteoblasts calcifies forming irregular areas of woven bone with osteocytes in lacunae and canniculi

bone forms gradually and is replaced by cancellous bone with marrow and larger blood vessels.

Question 17

Endochondral ossification

Answer 17

takes place within hyaline cartilage, shaped as a small version or model of the bone to be formed. it forms most bodies especially long bones

Question 18

Endochondral ossification process

Answer 18

1) late in first semester, bone collar develops beneath periosteum
2) capillaries invade and osteoprogenitor cells which produce a primary ossification center in diaphysis
3) osteoid is deposited by osteoblasts and under goes calcification into woven bone
4) remodeled into compact bone
5) at the time of birth, secondary ossification centers develop.
6) during childhood, primary and secondary ossification centers are separated by the epiphyseal plate which allows for continued bone elongation
7) two ossification centers do not merge until the epiphyseal plate disappears and the full stature is achieved

Question 19

Bone fracture repair

Answer 19

1) blood vessels torn within the fracture release blood that clots to produce a large fracture hematoma
2) clot gradually removed by macrophages and replaced by a soft fibrcartilage like mass called a procallus tissue. of torn by the break, the periosteum establishes its continuity over the tissue.
3) the procallus is invaded by regenerating blood vessels and proliferating osteoblasts. over the next few weeks fibrocartilage is replaced by woven bone that forms a hard callus.
4) over time the woven bone is remodeled to produce compact and cancellous bone

Question 20

spongey bone

Answer 20

1. LINED WITH OSTEOBLASTS (simple cuboidal layer) and OSTEOCLASTS (form a multinucleated large cell on spicule)
2. REMODELING HERE!

Question 21

compact bone

Answer 21

MANY OSTEONS

1. Osteocytes in lacunae
2. Haversian canals (neurovascular structure)

Question 22

osteopetrosis vs. ostoporosis

Answer 22

petrosis - heavy bones

porosis - brittle bones

Question 23

Parathyroid hormone

Answer 23

PTH → stimulates osteoblasts → secrete RANKL → mature osteoclasts → INCREASE Calcium in blood

Question 24

Calcitonin

Answer 24

Calcitonin → opposite → inhibits osteoclasts → Lower net reabsorption → DECREASE BLOOD CALCIUM

Question 25

Sharpey’s fibers

Answer 25

Interdigitations of collagen and bone periosteum outer layer

Question 26

histological prep of bone

Answer 26

know that newer formed osteons are darker, older are lighter 33.

Question 27

Describe the canals in osteon

Answer 27

(Haversion (CENTRAL) vs Volkmann’s (TRANSVERSE))