MSS 1 Bone Flashcards
Characteristis of osteoblasts?
Osteoblasts are specialized fibroblasts that make osteoid. Located in periosteum.
Cbfa-1: regulates osteoblast differentiation
Osteocalcin: deposition of calcium into osteoid
Characteristis of osteoclasts?
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.
Characteristis of osteocytes?
Osteocytes maintain bone matrix. They occupy lacunae between lamellae.
Distinguish between compact vs spongy bone.
Compact/ Cortical bone- dense, no cavitation. Spongy/Cancellous/trabecular: cavitation.
Distinguish between long vs. flat bones
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
What is the cellular mechanism by which bones develop?
Intramembranous: osteoblasts deposit osteoid onto mesoderm.
Endochondral: osteoblasts deposit osteoid onto cartilage
What are the growth factors that acclerate bone repair?
Bone orphogenetic proteins (BMPs) stimulates bone differentiation.
What are the mechanisms that regulate anti-resorptive and anabolic drugs for osteoporosis treatment?
Anabolic drug= pro-osteoblasts (PTH 1-34: teriparatide). Anti-resorptive drugs= anti-osteoclasts (SERM, raloxifene, biphosphonates, calcitonin).
What is the function of bone?
Provides infrastructure
Bone marrow
Resevoir of ca2+
What composes the matrix of bone?
Inorganic (70%): Ca2+ and phosphorus= hydroxyapatite
Organic (30%): osteoid= type 1 collagen, proteoglycans, glycoproteins: promotes hydroxyapatite formation (osteocalcin)
Why is bone so hard?
combined hydroxyapatite & collagen type I
Bone vs. cartilage: Mineral/ Water/ Collagen/ Neurovascular structure
Cartilage: no minerals, 75% water, Type II, no neurovascular structure
Bone: 70% minerals, 25% water, Type I collagen, neurovascular structures present
What are the components of osteoid?
Type I collagen and glycoproteins
What hormones regulate osteoclasts?
Calcitonin inhibits osteoclasts.
PTH: activates osteoclasts (Lysosomes make cathepskin K, H+ acidify environment)
What is an osteon?
An osteon is cylinder w/ concentric lamellae ( which have osteocytes), communicate via canaliculi and surrounds Haversian canal ( which have BV, Lymphs, nerves)
What is the process of bone formation at the diaphysis of long bones? At the epiphyses?
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
How do long bones get long? What are the different zones?
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)
What is the mechanism for fracture repair?
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.
What characterizes osteopetrosis? What is the defect?
Dense heavy bone. Osteoclasts lack ruffled border
What is osteoporosis? What characterizes it?
Resorption by osteoclasts outpaces osteogenesis= hollow fragile bones.
What is bone mineral densitometry?
BMD shows areas of bone density. Yellow/orange= low. T score is number of standard deviations below young normal mean.
What regulates osteoclast production?
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)
What inhibits osteoblasts? Osteoclasts?
Osteoblasts are inhibited by leptin. Osteoclasts are inhibited by calcitonin, osteoprotergrin.
What induces osteoblasts? Osteoclasts?
Osteoblasts are induced by BMP. Osteoclasts are induced by RANK-L. PTH induces both. Spkes of OTH–> osteoblasts production. Constant PTH–> osteoclasts.
