D4H4 Bone

Question 1

5 main functions of bone

Answer 1

1) support to resist physical stress
2) protection of soft organs
3) levers for muscle action
4) reservoir for calcium/phosphorus ions
5) blood cell production (marrow cavity)

Question 2

Why are long bones tubes, not rods?

Answer 2

• there’s no stress in middle of rod; the stress is all in the margin
• so that’s why you don’t deposit bone into middle
• space in middle lets you deposit other things in there

Question 3

spongy bone (cancellous or trabecular bone)

Answer 3

• allow for give

- spicules or trabeculae that support the interior of the bone metaphyses

Question 4

compact bone (dense)

Answer 4

-bigger & more robust lamellae (closely arranged layers of bone)

Question 5

diaphysis

Answer 5

middle part of bone

Question 6

metaphyses

Answer 6

transitioning from middle part of bone to epiphysis

Question 7

epihysis

Answer 7

ends of bones

Question 8

woven (aka primary) bone

Answer 8

• no sense of organization

- immature or non-lamellar, first to form during embryonic development and fracture repair

Question 9

lamellar (aka secondary) bone

Answer 9

• secondary or mature bone

- high mineral content, parallel collagen arrangement, composed of parallel or concentric thin layers of bone

Question 10

intramembranous ossification

Answer 10

• creating within the membrane
• mesenchyme –> osteoblasts (which then secrete osteoid)
• produces woven bone
• occurs in most of facial bones (parts of skull, jaw, clavicle), which are flat bones

Question 11

endochondral ossification

Answer 11

• osteoblasts produce osteoid on a pre-existing hyaline cartilage model
• produces woven bone
• occurs in long bones

Question 12

ossification (definition)

Answer 12

process of new bone formation on organic matrix

Question 13

What provides the toughness in bones?

Answer 13

• calcified extracellular matrix (ECM)

- this organic matrix is like scaffolding, mostly made up of collagen, proteoglycans, and glycoproteins

Question 14

What provides the hardness in bones?

Answer 14

• mineral crystals that precipitate within the organic matrix, and form the “cement”
• inorganic calcium and phosphate salts –> hydroxyapatite crystals

Question 15

osteoblasts

Answer 15

• bone forming cells (gonna “blast” you with bone)
• secrete osteoid
• found along periosteal and endosteal surfaces

Question 16

osteocytes

Answer 16

• “trapped” osteoblasts (cyte = cell, so these are bone cells)
• reside within lacunae (lacunae = coccoon-ae)
• communicate via canaliculi (small canals in bone)
• help maintain bone

Question 17

osteoclasts

Answer 17

• like bone macrophages, that eats bone for bone resorption
• large, motile, multinucleated cells
• produces an acidic enviro (via lysosomal enzymes and protons) to digest bone surface and crease Howship’s lacunae

Question 18

How are osteoclasts activated?

Answer 18

Parathyroid hormone activates osteoblast –> osteoblasts release RANKL –> this activates osteoclasts –> osteoclasts begin resorption of bone –> this releases calcium into the blood

Question 19

endosteum

Answer 19

• line the central cavity of bones and trabeculae

- helps the bone grow from the inside (has osteoprogenitor cells, osteoblasts, osteoclasts)

Question 20

periosteum

Answer 20

• 2 layers:
  1) outer dense connective tissue (connected to exterior surface of bone)
  2) inner cellular layer (w/ osteoprogenitor cells and osteoblasts)

Question 21

woven (immature or non-lamellar) bone

Answer 21

• primary bone (1st to form during embryonic development, fracture repair)
• low mineral content, irregular collagen bundles, many osteocytes
• replaced by lamellar bone later

Question 22

lamellar bone

Answer 22

• secondary (mature) bone
• high mineral content, parallel collagen arrangement, has parallel or concentric layers of bone
• can be spongy or compact bone
• replaces woven (primary) bone

Question 23

lamellae

Answer 23

layers of bone

Question 24

ossification

Answer 24

process of new bone formation on organic matrix

Question 25

calcifcation

Answer 25

formation of mineral salts in soft tissue

Question 26

interstitial vs appositional growth

Answer 26

• interstitial = I (looong) = growth in length of bones

- appositional growth = fat Apple = growth in width

Question 27

hormonal control of osteoclasts/osteoblasts

Answer 27

low serum calcium level: parathyroid gland releases parathyroid hormone –> sends message to osteoblasts –> stimulates osteoclasts to eat at bone –> liberate calcium ions into serum

high serum calcium level: thyroid gland makes calcitonin –> inhibits osteoclast activity –> calcium NOT released, instead calcium deposited in bones

Question 28

scurvy

Answer 28

• vitamin C deficiency

- impairs collagen and osteoid secretion

Question 29

rickets

Answer 29

• calcium/phosphate or vitamin D deficiency in kids
• bone poorly mineralized/bone deformities
• bowed/knock-kneed legs (think rickety stairs)

Question 30

osteomalacia

Answer 30

• phosphate or vitamin D deficiency in adults
• bone poorly mineralized
• osteo (bone) is “mal” (bad)

Question 31

osteoporosis

Answer 31

• rate of bone resorption is greater than bone deposition
• loss of bone strength
• ostea (bone) pores (holes) –> weak bones

Question 32

osteopenia

Answer 32

• pre-osteoporosis
• lower mineral density
• not yet at osteoporsis, but still a “pain” (penia)

Question 33

osteopetrosis

Answer 33

• impaired osteoclast function –> failure to remodel bone properly –> loss of normal marrow compartment
• more mineralized bone = more brittle and prone to fracture
• “petrified”, so hard and brittle