Cartilage and Bone Flashcards
Cartilage consists of
cells (chondrocytes), ground substance, extracellular fibers
Histology of cartilage
pink background- matrix; dark pink and provides blood supply- perichondrium; gaps- lacunae housing the chondrocytes
Shock absorbing characterstic of hyalin cartilage
Due to water binding to negatively charged proteoglycans and is squeezed out of cartilage upon compression and comes back and binds to proteoglycan again when relaxed
Rigidity of hyalin cartilage
Due to interactions between type 2 collagen fibrils and GAGs
GAG
glycosaminoglycans: proteoglycans in cross linked matrix with hyaluronic acid
matrix components of cartilage
GAGs (chondroitin 4 sulfate, chondroitin 6 sulfate, keratan sulfate, and hyaluronic acid) and adhesive molecule (chondronectin)
synthesis of GAG
amino acids put together in the RER and sugars added in golgi apparatus
cartilage nutrition
cartilage lacks vasculature so nutrients must come in through diffusion; nutrients provided via perichondrium
3 types of bone cells
osteoblasts, osteoclasts, osteocytes
two types of long bones
compact, lamellar, or cortical bone; cancellous (trabecular) bone
compact bone
lamellar, cortical; dense area without cavities
cancellous bone
3-d lattice of branching bony spicules, forming tabeculae around narrow spaces
geography of long bone
epiphyses- two ends
diaphysis- shaft
metaphysis- growth plate between epiphyses and diaphysis
composition of bone matrix
35% organic matrix and 65% inorganic salts
organic matrix of bone
35% of bone; extracellular organic phase, composed of proteins (exogenously derived and trapped growth factors), glycoproteins, and proteoglycans synthesized by the osteogenic cell;
consists of type 1 collagen fibers (85-90%) embedded in an amorphous ground substance
inorganic content
65%; hydroxyapatite crystals [Ca10(OH2)(PO4)6]
osteoprogenitor cells
pluripotential, stem cells from mesenchyme; can differentiate into osteogenic cells-osteoblasts; found in periosteum and endosteum as bone lining cells and differentiate into osteoblasts following a fracture
osteblasts
synthesize and secrete the organic matrix of bone: type 1 collagen and non collagenous proteins and alkaline phosphatase
osteocytes
calcified osteoblasts; communicate via gap junctions
osteoclasts
multinucleated cells derived from monocytes; produce an acidic environment ideal for dissolution of bone matrix; plasmalemma of the osteoclast is thrown into folds and villous like processes constituting the ruffled border
origin of bone cells
mesenchyme–> osteoprogenitor –>osteoblasts (–> osteocytes) OR bone lining cells (stem cells);
bone marrow monocyte precursors–> monocytes–> osteoclasts
osteoblasts synthesize
osteoid, alkaline phosphatase, noncollagenous proteins
osteoid
type 1 collagen and proteoglycans
noncollagenous proteins synthesized by noncollagenous proteins
RANK-L- stimulated osteoclastogenesis Osteoprotegerin inhibiting factor- decoy receptor for RANK-L growth factors osteocalcin- mineralization osteopontin- forms sealing zones
skull
external table, diploe, internal table
architecture of long bone
periosteum and endosteum
periosteum
bone is surrounded by dense CT- has osteoprogenitor cells
absent at articulating surfaces and at attachment of tendons and ligaments
endosteum
lining the marrow cavity and have osteoprogenitor cells lining
ground substance
glycoproteins, glycosaminoglycans, proteoglycans, GF, peptides
calcium phosphate
magnesium phosphate
ARF cycle
activation–> resorption (by osteoclasts)–> reversal (osteoblasts grow)–> formation–> resting phase–> activation
PTH
parathyroid hormone; decreased blood calcium stimulates PTH–> bone releases calcium by increasing osteoclasts and ruffled border activity–> kidneys conserve Ca++–> intestine absorbs Ca++;
increased blood calcium inhibits PTH secretion (inhibitory)
Calcitonin
opposite of PTH; C cells of thyroid gland and decreases serum Ca++
osteoclasts in presence of PTH
do not have receptor for PTH; osteoblasts release RANK-L which binds to RANK on osteoclasts and pre-osteoclasats which increases activity of ruffle border
(osteoprotegrin counter RANK-L)
bisphosphonates
kill osteoclasts via apoptosis; inhibits osteoclast recruitment
MCSF and OPG
- Monocytes derived from vessels in the bone marrow express M-CSF receptor on their cell surface. 2. M-CSF binds to M-CSF receptor and induces the expression of RANK. 3. RANK ligand (RANKL) is produced by stromal cells/osteoblasts and binds to the receptor, RANK, on mononuclear osteoclast progenitors. 4. OPG, a decoy receptor that binds to RANKL and inhibits osteoclast differentiation. 5. Multiple factors including hormones and locally produced cytokines/growth factors and matrix proteins, mediate the activation (bone resorption) of osteoclasts
types of cartilage
hyaline, elastic, fibrocartilage
hyaline cartilage
in external auditory meatus, cartilage models of long bones; type 2 collagen; perichondrium (dense CT surrounding cartilage)
elastic cartilage
in pinna of ear and larynx; type 2 collagen and elastic fibers; perichodnrium
fibrocartilage
in intervertebral disks, pubic symphysis; type 1 collagen, no perichondrium
vitamin D
decrease in vitamin D increases calcium secretion from bones; vitamin D inhibits PTH
denosumab
inhibits rank-L
