SCLEROUS TISSUE
•Cartilage
•Bone
CELLS OF BONE TISSUE
Solidified Matrix / Special / Skeletal Tissue
1- Cartilage
•Chondrous /cartilaginous/non-mineralized tissue
2– Bone
•Osseous/bony/mineralilzed tissue
“Bone is a specialized type of C.T. composed of calcified intercellular material, bone matrix & 3 cell types”.
Organic component
INORGANIC (MINERAL) COMPONENT (65%)
•The association of minerals with collagen fibers is responsible for hardness & resistance of bone
•Main components…….Ca & phosphorus {crystalline most abundant (hydroxyapatite); rod like crystals, non crystalline Ca PO4}
•Substantial quantities of Na, K, Mg, HCO3 & Citrate
•If we remove organic component of bone……
•If we remove inorganic component of bone…….
CELLS OF BONE TISSUE
CELLS OF BONE TISSUE
1.OSTEOPROGENITOR CELLS
•Developed from
•Present in
•Shape
•Nuclei
•Cytoplasm
•Under E/M
•Become active during growth and healing of bone.
•Can differentiate into Osteoblasts
2. OSTEOBLASTS
ÒDerived from
ÒSpecialized, non-dividing bone-forming cells
ÒSynthesize & secrete organic comp (OSTEOID) & AlkPO4
ÒUnder L/M
ÒUnder E/M
ÒTransforms into
ÒCytoplasmic-
processes
ÒGap junctions
ÒReceptors for PTH
ÒSecrete a cytokine
ÒOsteoclast stimulating factor
3. OSTEOCYTES
ÒMature bone cells
ÒDerived from
ÒNot capable of mitosis but are long living cells
ÒUnder L/M
ÒUnder E/M
ÒLacunae
ÒCanaliculi
ÒPeriosteocytic space
ÒCytoplasmic processes
ÒGap junctions
ÒMajor functions…..maintenance of bone matrix, & maintenance of adequate Ca level
4. OSTEOCLASTS
ÒDerived from
ÒSpecially meant for resorption of bone matrix
ÒImp for remodelling & renewal of bone
ÒFound where
ÒResorption bays (Howship’s lacunae)
ÒLarge, multinucleated, motile cells
ÒStrongly Acidophilic cytoplasm
ÒRuffled border & Clear zone
ÒSubosteoclastic compartment
ÒSecrete H+ ions, collagenase
& hydrolytic enzymes
ÒReceptors for calcitonin
Bone resorption by osteoclast
COMPARISON AMONG BONE CELLS
Osteoblasts secrete the matrix which then hardens by calcification, trapping the differentiating cells now called osteocytes in individual lacunae.
Osteocytes maintain the calcified matrix and receive nutrients from blood vessels via very small channels through the matrix called canaliculi.
Osteoclasts are monocyte—derived cells in bone which are important in bone remodeling.
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