Bone Flashcards
(40 cards)
Makes up the epiphysis:
-cancellous
-medullary
-trabecular
Matrix is lamellar and only has osteons if it’s sufficiently thick
-marrow cavity diffusion nourishes it
-woven bone
Spongy bones
Consist of: woven bone
-interstitial lamellae between osteons
-circumferential lamellae beneath periosteum beneath endosteum of marrow cavity & reticular tissue (in)
-periosteum with volkmann’s canals (out)
-Sharpey’s fibers (out)
-osteogenic cells (in)
Compact bone
Hollow cylinder of long bone filled with spongy bone and bone marrow
Medullary cavity
-Mechanosensor using piezoelectricity & fluid
-surrounded by transported bone fluid
-promotes CaPO4 disposition by lacking PPi
-form gap junctions with osteoblasts
-stimulate/ inhibit osteoblasts
Osteocytes
-produces ECM & cytokines
-deposits Ca2+ & Pi into matrix via vesicles
-target of PTH, estrogen, IGF-1,& vitamin D
-High alkaline phosphatase (ALP) activity
-basophilic cytoplasm & cuboidal
-secrete osteoid
-integrins anchored it via sialoprotein
Osteoblasts
-RANK ligand (RANKL)
-osteoprotegerin (OPG)
Cytokines
Receptor activator of nuclear factor kB on the surface of osteoclasts and activates them
-Decreased by estrogen influenced osteoblasts
-stimulated by PTH
-osteoprotegerin blocks RANK binding
RANKL
Competitively binds to RANKL and prevents it from activating RANK
OPG
-Stimulates osteoclasts function indirectly through osteoblasts (short-t) activation
-increase Ca2+ serum
-increase bone resorption of Ca2+
-increase renal resorption of Ca2+
-activate vitamin D in kidney (calcitriol)
-decrease renal PO4 reabsorption (long-t), in ECF
PTH
Formed by: type I collagen (procollagen)
-osteocalcin & non-collagen proteins, GAGs, Proteoglycans, 🦴 sialoprotein, osteopontin
Acts as a scaffold for deposition of minerals
Osteoid
-Prevents Ca2+ & Pi precipitation by breaking down phosphate (PPi)
- promotes bone mineralization
ALP
-Stimulates osteoblast differentiation & increases OPG release
-inhibit/ stimulate osteoclasts & osteoblasts
-vitamin D, in stratum basale & spinosum
-increase Ca2+ & PO4 serum & intestinal absorption 🥛
Calcitriol
-Create Howship’s lacuna and releases acid into it so that Ca2+ & Pi are dissolved
-release proteolytic enzymes to break down collagen fibers
-integrins anchored it via osteopontin
-active after sealing zone and ruffled border appears
-multinucleated monocyte from 🦴 marrow
Osteoclasts
-Piezoelectricity in bone
-bone will remodel to meet its mechanical demands
Wolff’s law
-osteonectin binds it to type I collagen -sequestered into mitochondria & ER to keep intracellular Ca2+ low
-50% ionized formed
-40% albumin bound
-10% PO4 & citrate anion complexed
Pi bind to Ca2+
Hydroxyapatite crystals
-decrease Ca2+ & PO4 serum by inhibiting: dietary Ca2+ absorption
-osteoblastic resorption
-osteoclasts
-renal reabsorption of Ca2+ & PO4
Calcitonin
-trabeculae replaced by compact 🦴
-lamellar 🦴 is formed
3weeks
Hard callous remodeling
Hyaline cartilage chondrocytes hypertrophy
-VEGF is released (vascularize perichondrium & make bone collar)
Under high O2 tension
-woven 🦴 replaces cartilage via endochondral 🦴 formation
-In shaft 2-3weeks
Bony callus formation
-phagocytic cells remove dead tissue
-osteogenitor cells differentiate into chondroblasts in low O2 tension
- granulation tissue becomes hyaline cartilage
-fractured 🦴 bonded
1-2weeks
Soft callus formation
Clot forms from granulation tissue
5days
Procallus formation
Decreased by estrogen influenced osteoclasts
-start osteoclastogenesis when RANKL expressed by osteoblasts binds to it
RANK
Transverse
-house periosteal arteries
Volkmann’s canal
Nutrient & periosteal artery vascular supply
-scapula, vertebrae, os coxae
-have multiple primary & secondary ossification centers
-undergoes endochondral bone formation from hyaline cartilage
Irregular bone
Nutrient & periosteal artery vascular supply
-skull & sternum
-intramembranous 🦴 formation from mesenchyme occurs here (has anastomosing trabeculae)
Flat bone
