4. BONE
• bone is a specialized form of dense connective tissue.
• The most hard of all connective tissues.
• Bone is the main component of the skeleton in the adult human.
• Bone gives the skeleton the necessary rigidity to function as
attachment and lever for muscles and supports the body against gravity.
8. HISTOLOGY
• Histos means Tissue logy means study
• Histology ---- Microscopic Anatomy
• Histology is mainly the study of microscopic structures like cells and tissues.
9. HISTOLOGY OF BONE
• Like other Connective Tissue, the bone is composed of cells and
matrix.
11. BONE CELLS
• Four types of cells are found in Bone.
1. Osteoprogenitor cells (or stem cells of bone)
2. Osteoblasts (Bone Forming Cells)
3. Osteocytes ( Mature Bone Cells)
4. Osteoclasts (Bone Resorbing Cells)
12. OSTEOPROGENITOR CELLS
• A stem cell that is the precursor of an osteoblast.
• Osteogenic cells are the only bone cells that divide.
• Osteogenic cells differentiate and develop into OSTEOBLASTS which, in turn, are
responsible for forming new bone.
• Osteoprogenitor cells are located in the inner cellular layer of the periosteum and the
endosteum.
13. OSTEOBLASTS
• Osteoblasts are bone forming cells.
• They originate from osteoprogenitor cells.
• They synthesize unmineralized bone matrix (Osteoid) and Alkaline Phosphatase that
bring about mineralization of osteoid.
• Active Osteoblasts are large cells and posses cytoplasmic processes which make contact
with those of other cells.
• Inactive osteoblasts are fusiform cells.
• they become trapped in their own secretions and differentiate into Osteocytes.
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15. OSTEOCYTES
• Osteocytes are mature bone cells and they are derived from Osteoblasts.
• Osteocytes are star shaped cells with fine cytoplasmic process.
• Osteocytes have an average half life of 25 years.
• Osteocytes lie within small cavities called lacunae.
• Although osteocytes are relatively inert cells Osteocytes synthesize sclerostin, a secreted
protein that inhibits bone formation by binding to LRP5/LRP6 coreceptors.
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17. OSTEOCLASTS
• Osteoclasts are bone resorbing cells.
• They are multinucleated giant cells containing 30 or more nuclei.
• Found in close association with bone surface located in shallow grooves called
Howship’s Lacunae.
• Osteoclasts secret several organic acids and lysosomal enzymes (cathepsin C, beta-
glycerophosphatase, beta-glucuronidase). Acids dissolve mineral component while
enzymes destroy organic matrix.
20. BONE MATRIX
• Bone matrix consist of :
1. Organic component
• Constitutes 35% of dry weight of bone.
• Consist of (i) Collagen Fibers & (ii) amorphous ground substance.
• Collagen fibers are type-I, making 95% of organic mass.
2. Inorganic Component
• Constitutes 65% of dry weight of bone.
• Calcium phosphate is the chief bone mineral deposited as crystal of calcium
hydroxyapatite over collagen fibers
22. MICROSCOPIC ARRANGEMENT
• The bone matrix is arrange in layers know as Lamellae.
• There are three type of lamellae based on their arrangement.
1. Concentric lamellae (surrounds Haversian canal)
2. Interstitial lamellae (present between two Haversian systems)
3. Circumferential lamellae (Present at periphery)
• The bone cells are present within spaces called lacunae between the lamellae.
• The Haversian canal is a longitudinal canal, around which lamellae are arranged in a
regular manner.
• Some small canals pierces the bone from periosteum and endosteum, these channels
are called Volkmann's canals.
• Periosteum: thick fibrous sheath covers the bone at outer side except articular
surfaces.
• Endosteum: Thin layer of connective tissue that lines the medullary cavity.
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25. Q#1: THE ONLY BONE OF THE BODY
WHICH IS VISIBLE TO EVERYONE?
