090314 bone

Question 1

how is bone specialized CT?

Answer 1

it is CALCIFIED extracellular matrix

Question 2

what is bone a reservoir of

Answer 2

Ca, phosphate

Question 3

what 3 cell types are in bone?

Answer 3

osteoblasts
osteocytes (maintain bone)
osteoclasts (activated by PTH of the parathyroid, inhibited by calcitonin of the thyroid)

Question 4

what is in the matrix of bone?

Answer 4

inorganic stuff is 70%

organic stuff is 30%

Question 5

what’s in the inorganic stuff of the matrix of bone?

Answer 5

Ca + phosphorus = hydroxyapatite

Question 6

what’s in the organic stuff of the matrix of bone?

Answer 6

type I collagen
proteoglycans (less than in cartilage)
glycoproteins (promote hydroxyapatite formation)

Question 7

what does type I collagen stain

Answer 7

acidophilia, red

Question 8

what is a glycoprotein that is bone specific?

Answer 8

osteocalcin

Question 9

what is the organic matter of the matrix of bone called?

Answer 9

the osteoid

Question 10

why is bone so hard?

Answer 10

combined hydroxyapatite AND collagen type I

Question 11

diff btwn bone and cartilage?

Answer 11

bone has 70% hydroxyapatite/mineral content, whereas hyaline cartilage has none

bone is 25% water, hyaline cartilage is 75%

bone has type I collagen, hyaline cartilage has type II (softer) collagen

bone has neuronal and vascular structures, but hyaline cartilage has none

Question 12

osteoblasts are what kind of cell

Answer 12

fibroblast (specialized)

Question 13

the only osteoblast specific genes

Answer 13

Cbfa-1 (master gene transcription factor)

Osteocalcin

Question 14

what growth factors induce osteoblast differentiation?

Answer 14

bone morphogenetic proteins (BMPs)

Question 15

what do osteoblasts do?

Answer 15

make osteoid (type I collagen and glycoproteins)

Question 16

how is bone formation completed?

Answer 16

osteocalcin-mediated deposition of calcium within the osteoid

Question 17

what do osteocytes occupy

Answer 17

lacunae (1 osteocyte per lacuna)

Question 18

what is the function of osteocytes

Answer 18

maintaining bone matrix

Question 19

what runs in the canaliculi of lacuna?

Answer 19

the cytoplasmic processes of osteocytes (they extend to join those of other osteocytes via gap jxns)

Question 20

role of osteoclasts

Answer 20

destroy or remodel bone matrix

Question 21

what is special about the nucleus of osteoclasts

Answer 21

multinuclear-developed from macrophages that fused together

Question 22

where do osteoclasts reside

Answer 22

hollow areas of matrix called Howship’s lacunae

Question 23

what does the ruffled border of the osteoclast do?

Answer 23

attaches to ECM and provides microenvironment promoting bone resorption

Question 24

how are osteoclasts regulated?

Answer 24

by HORMONES (calcitonin, PTH)

Question 25

how does PTH activate an osteoclast

Answer 25

lysosomes manufacture cathepsin K, which is secreted into microenvironment; promotes secretion of acid, which activates the Cathepsin K

Question 26

where are cells of bone located

Answer 26

osteoblasts-periosteum, with smaller numbers in endosteum osteocytes-within lacunae of bony matrix between periosteum and endosteum osteoclasts-mostly attached to bony matrix on endosteal side

Question 27

compact bone

Answer 27

also called cortical bone dense, no cavitation

Question 28

spongy bone

Answer 28

also called cancellous, trabecular bone has cavitations

Question 29

microscopic appearance of compact vs spongy bone

Answer 29

identical

Question 30

flat bone

Answer 30

2 plates of compact bone surrounding diploe of spongy bone

Question 31

long bones

Answer 31

have diaphysis and epiphyses diaphysis is compact with spongy bone lining marrow epiphysis has cap of compact bone around spongy bone

Question 32

osteon

Answer 32

cylinder in long bone with concentric lamellae

Question 33

what does the innermost lamella in an osteon surround

Answer 33

Haversian canal

Question 34

HOw are Haversian canals connected

Answer 34

volkmann's canals

Question 35

primary bone vs secondary bone

Answer 35

primary is immature (fetus, or broken bone, or in remodeling process) secondary is mature/lamellar

Question 36

two ways in which bone develops

Answer 36

intramembranous (osteoblasts deposit osteoid onto mesoderm) endochondral (osteoblasts deposit osteoid onto cartilage)

Question 37

endochondral bone development

Answer 37

bone forms on hyaline cartilage at diaphysis-osteoblasts invade CALCIFIED cartilage--secrete osteoid to get ossification at the epiphyses-same process as above. articular cartilage remains at ends of bones. epiphyseal plate cartilage remains for growth in length for fetus development and natural repair of fractures

Question 38

how do long bones get long (part one)

Answer 38

sex steroid hormones influence pituitary, which secretes growth hormone (GH/somatotropin), which caues liver to make somatomedin (or IGF-1), which goes to the epiphyseal plate at epiphyseal plate: there's reserve cartilage, and beneath that-there's a zone of proliferation, which is induced by somatomedin (IGF-1)

Question 39

how do long bones get long (part two)

Answer 39

the zone of proliferation has chondrocytes next is the zone of hypertrophy (20% of fractures)

Question 40

how do long bones get long (part three)

Answer 40

next is the zone of calcification (basophilic), where you will find collagen X, not collagen II). This will be calcified cartilage. next is the zone of ossification, which is eosinophilic due to the deposition of collagen I by osteoblasts

Question 41

how does fracture repair occur?

Answer 41

macrophages remove debris chondroblasts secrete callus of hyaline cartilage osteoblasts replace cartilaginous callus with bony callus primary bone replaced by secondary bone

Question 42

what happens with difficult fractures that don't heal?

Answer 42

they require grafting

Question 43

what are therapeutic targets for osteoporosis

Answer 43

osteoclasts and osteoblasts

Question 44

how are osteoclasts regulated by PTH?

Answer 44

stromal cells in bone marrow are induce by PTH to secrete three factors that regulate osteoclasts the three factors are: RANKL, OPG, M-CSF

Question 45

role of M-CSF

Answer 45

induces macrophage proliferation

Question 46

RANK-L

Answer 46

induces macrophage differentiation into osteoclasts

Question 47

OPG

Answer 47

osteoprotegerin - it antagonizes RANK-L by binding to its receptor

Question 48

alpha5beta3

Answer 48

enalbes attachment of osteoclasts to bone

Question 49

leptin has what action

Answer 49

inhibts osteoblasts

Question 50

what is induced by PTH?

Answer 50

osteoblasts (when there's spikes of PTH) and osteoclasts

Question 51

anabolic drugs

Answer 51

pro-osteoblast PTH 1-34 (teriparatide/Forteo)

Question 52

anti resorptive drugs

Answer 52

anti-osteoclast SERMs (raloxifene) bisphosphonates (ibandronate/Boniva) calcitonin