MSS 1 Bone

Question 1

Characteristis of osteoblasts?

Answer 1

Osteoblasts are specialized fibroblasts that make osteoid. Located in periosteum.
Cbfa-1: regulates osteoblast differentiation
Osteocalcin: deposition of calcium into osteoid

Question 2

Characteristis of osteoclasts?

Answer 2

Osteoclasts destroy/remodel bone matrix. They develop from macrophages that fuse together. They reside in Howship’s lacunae. Ruffled border of the osteoclasts form a microenvironment that promotes bone resorption. Found attached to bony matrix on endosteal side.

Question 3

Characteristis of osteocytes?

Answer 3

Osteocytes maintain bone matrix. They occupy lacunae between lamellae.

Question 4

Distinguish between compact vs spongy bone.

Answer 4

Compact/ Cortical bone- dense, no cavitation. Spongy/Cancellous/trabecular: cavitation.

Question 5

Distinguish between long vs. flat bones

Answer 5

Flat bones: 2 plates of compact bone surround diploe of spongy bone.
Long bones: Diaphysis- compact w/ spongy bone lining marrow. Epiphyses: caps of compact bone around spongy bone

Question 6

What is the cellular mechanism by which bones develop?

Answer 6

Intramembranous: osteoblasts deposit osteoid onto mesoderm.
Endochondral: osteoblasts deposit osteoid onto cartilage

Question 7

What are the growth factors that acclerate bone repair?

Answer 7

Bone orphogenetic proteins (BMPs) stimulates bone differentiation.

Question 8

What are the mechanisms that regulate anti-resorptive and anabolic drugs for osteoporosis treatment?

Answer 8

Anabolic drug= pro-osteoblasts (PTH 1-34: teriparatide). Anti-resorptive drugs= anti-osteoclasts (SERM, raloxifene, biphosphonates, calcitonin).

Question 9

What is the function of bone?

Answer 9

Provides infrastructure
Bone marrow
Resevoir of ca2+

Question 10

What composes the matrix of bone?

Answer 10

Inorganic (70%): Ca2+ and phosphorus= hydroxyapatite
Organic (30%): osteoid= type 1 collagen, proteoglycans, glycoproteins: promotes hydroxyapatite formation (osteocalcin)

Question 11

Why is bone so hard?

Answer 11

combined hydroxyapatite & collagen type I

Question 12

Bone vs. cartilage: Mineral/ Water/ Collagen/ Neurovascular structure

Answer 12

Cartilage: no minerals, 75% water, Type II, no neurovascular structure
Bone: 70% minerals, 25% water, Type I collagen, neurovascular structures present

Question 13

What are the components of osteoid?

Answer 13

Type I collagen and glycoproteins

Question 14

What hormones regulate osteoclasts?

Answer 14

Calcitonin inhibits osteoclasts.
PTH: activates osteoclasts (Lysosomes make cathepskin K, H+ acidify environment)

Question 15

What is an osteon?

Answer 15

An osteon is cylinder w/ concentric lamellae ( which have osteocytes), communicate via canaliculi and surrounds Haversian canal ( which have BV, Lymphs, nerves)

Question 16

What is the process of bone formation at the diaphysis of long bones? At the epiphyses?

Answer 16

Bone forms on hyaline cartilage.
Diaphysis: osteoblasts invade calcified cartilage and secrete osteoid–> ossification
Epiphyses: by the same proces but articular cartilage remains at the ends of bones. Epiphyseal plate cartilage remains for growth in length

Question 17

How do long bones get long? What are the different zones?

Answer 17

Sex steroid hormones–> pituitary–> GH; somatrophin-> liver–> somatomedin (IGF-1)–>epiphyseal plate.
Zone of proliferation; induced by somatomedin
Zone of hypertrophy:
Zone of calcification (calcified cartilage)– Collagen X (basophilic)
Zone of ossification: deposition of Collagen I by osteoblasts (eosinophilic)

Question 18

What is the mechanism for fracture repair?

Answer 18

Macrophages remove debris–> chondroblasts secrete a callus of hyaline cartilage–> Osteoblasts replace cartilaginous callus w/ bony callus. Primary bone is replaced by lamellar secondary bone.

Question 19

What characterizes osteopetrosis? What is the defect?

Answer 19

Dense heavy bone. Osteoclasts lack ruffled border

Question 20

What is osteoporosis? What characterizes it?

Answer 20

Resorption by osteoclasts outpaces osteogenesis= hollow fragile bones.

Question 21

What is bone mineral densitometry?

Answer 21

BMD shows areas of bone density. Yellow/orange= low. T score is number of standard deviations below young normal mean.

Question 22

What regulates osteoclast production?

Answer 22

M-CSF ( induces macrophage prolferation)
RANK-L (induces macrophage differentiation into osteoclasts (receptor for NfKB)
OPG (Osteoprotegrin antagonizes RANK-L by binding to its receptor)

Question 23

What inhibits osteoblasts? Osteoclasts?

Answer 23

Osteoblasts are inhibited by leptin. Osteoclasts are inhibited by calcitonin, osteoprotergrin.

Question 24

What induces osteoblasts? Osteoclasts?

Answer 24

Osteoblasts are induced by BMP. Osteoclasts are induced by RANK-L. PTH induces both. Spkes of OTH–> osteoblasts production. Constant PTH–> osteoclasts.