Bone 1 PDF, SAM 2024

Bone 1 By staff member of histology General Characters of Bone 1- It is a special type of connective tissue with hard matrix. Function of bone: 1. Forms body skeleton and protects vital organ. 2. Acts as a store of Ca and other ions. 3. Contains bone morrow, the factory of blood cells. ...

Bone 1 By staff member of histology General Characters of Bone 1- It is a special type of connective tissue with hard matrix. Function of bone: 1. Forms body skeleton and protects vital organ. 2. Acts as a store of Ca and other ions. 3. Contains bone morrow, the factory of blood cells.  Structure of bone: A.Cells: B.Matrix 1. Osteogenic (osteoprogenitor) 1. Organic component ▪ Mainly type I collagen fibers "90% of organic 2. Osteoblasts matrix". 3. Osteocytes ▪ Ground substance: proteoglycans glycoprotein. 4. Osteoclasts 1. Inorganic component: Calcium, phosphorous. Bone cells  Bone Cells: 1- Osteogenic (osteoprogenitor) cells Origin: Mesenchymal stem cells Site: periosteum and endosteum LM: Flat cell, faint basophilic and pale nucleus. EM: Free ribosomes Function: they give rise to osteoblasts  2- Osteoblasts (bone forming cells) Origin: osteogenic cells Site: the same as osteogenic LM: Large rounded cells with short processes. Deep Basophilic cytoplasm(-ve Golgi image) EM: (protein secreting cells). Abundant RER and free ribosomes, Well-developed Golgi apparatus with numerous mitochondria Function: (Bone forming cells): 1. Secretion of bone matrix. 2. Calcification (mineralization) of bone matrix. 3. Transformed into osteocytes. 3- Osteocytes (bone maintaining cells) Origin: Osteoblasts imprisoned in lacuna and surrounded by hard matrix. LM: Small, branched cells present inside lacunae, weak basophilic cytoplasm, and oval nuclei. EM: RER, Golgi apparatus, and mitochondria. Cytoplasmic processes extend through canaliculi in bone matrix to contact processes of neighboring cells. Function: Osteocytes maintain the calcified Matrix. 4- Osteoclasts (Bone-eating cells) Origin: from the fusion of monocytes. Site: Occupy shallow depressions in bone matrix called "Howshipꞌs lacunae". Endosteum LM: Large cell with striated (ruffled) border. Strongly acidophilic cytoplasm. Multinucleated (5- 50 nuclei). Function: Bone resorption during osteogenesis, growth & repair by releasing lysosomal enzymes into extracellular space.  Osteoprogenitor Osteoblast Osteocyte Osteoclast Origin Undifferentiated Osteoprogenitor Osteoblast Blood monocytes mesenchymal cells LM: Shape Small ( few organelles) large rounded cells with Flattened with Giant (resulted from Flat cell short processes. processes fusion of 50 cells) Irregular with ruffled border. Nucleus Oval,pale (division) Eccentric, pale Dark Multinucleated (up to 50) Pale basophilic (few Cytoplasm organelles mainly free Deep basophilic (rER) & Pale basophilic Deep acidophilic ribosomes) negative Golgi image ( ( moderate (mitochondria) & Golgi) organelles) vacuolated ( lysosomes) Types Osteoprogenitor Osteoblast Osteocyte Osteoclast EM few organelles mainly Protein synthesizing cell Moderate amount of Large number of free ribosomes for abundant rER, Golgi& organelles (less active) lysosomes (resorption), division secretory vesicles. Cells are within lacunae. Processes are within canaliculi. Sites 1- inner cellular layer of The same as Within lacunae while - Within depressions periosteum. osteoprogenitor their processes within called Howship s 2- endosteum canaliculi. lacunae. 3- lining Haversian - endoesteum canal.  Osteoprogenitor Osteoblast Osteocyte Osteoclast Functions The mother cell of the Bone forming cell The unit bone cell; The bone eating cell; bone; 1- secretion of organic maintain matrix bone resorption during Divide and give matrix. osteogenesis, growth & osteoblasts 2- precipitate Ca repair. (calcification) 3- transformed into osteocytes.  Types of Bone Compact Bone Spongy Bone 1. Compact bone: Dense, hard and without cavities. In outer layer of all bones (especially shaft of long bones)  Structure of compact bone a- Periosteum. b- Endosteum. c- Haversian system. d- outer circumferential bone lamellae. e. Inner circumferential bone lamellae f- Interstitial bone lamellae. g- Volkmann's canal. a. Periosteum Covers the outer surface of the bone. It consists of 2 layers: - Outer (fibrous) layer: formed of dense C.T. and blood vessels. - Inner Cellular: osteogenic cells and osteoblasts.  b. Endosteum 1. Single layer of osteogenic cells. 2. Lines marrow cavities. c. Haversian system (osteon): Structural unit of compact bone formed of:.Haversian canal: loose CT rich in blood vessels and nerves. runs parallel to long axis of bone..Concentric bone lamellae: which are calcified osteoid tissue arranged in concentric layers (4-20 layers) separated by osteocytes inside lacunae. d. Volkmann's Canals: Transverse or oblique canals that connect haversian canals together and with periosteum and endosteum. e. Inner circumferential lamellae: Calcified osteoid tissue parallel to endosteum. f. Outer circumferential lamellae: Calcified osteoid tissue parallel to periosteum. g. Interstitial Lamellae: Irregularly arranged lamellae in-between haversian systems.  2. Spongy bone Spongy-like meshwork with cavities. Site: interior of all bones mainly flat bones. Structure: Irregular trabeculae of bone tissue Numerous interconnecting bone marrow spaces. Bone marrow cavity Osteoid tissue / bone trabecul ae  Thank you And KEEP SMILING