General Histology: Bone (Supporting CT) PDF - Lecture Notes, 11/9/2024

11/9/2024 Course Title : General Histology Lecture Title : Bone (supporting CT) Lecturer Name : Omayma Kamel Afifi Professor of Histology & Cell Biology, Faculty of Medicine, Tanta University Asso...

11/9/2024 Course Title : General Histology Lecture Title : Bone (supporting CT) Lecturer Name : Omayma Kamel Afifi Professor of Histology & Cell Biology, Faculty of Medicine, Tanta University Associate Trainer In IBCT and NCFLD Arbitrator in the Promotion Committee of the Supreme Council Reviewer in NAQAAE Prof Dr Omayma Kamel Afifi 1 Lecture ILOs/ Objectives: Identify the structural characteristics of the bone & how to prepare Distinguish between different types of bone cells Differentiate between the microscopic structure of different bone types. Differentiate between cartilage and bone Prof Dr Omayma Kamel Afifi 2 1  11/9/2024 II-Bone A specialized CT whose extracellular matrix is calcified. 1- Protects & supports vital organs of the body as brain & spinal cord 2- A storage site for the calcium & phosphate. 3- Contains bone marrow which acts as a haemopoietic organ. 4- Serves as a lever for skeletal muscles. Prof Dr Omayma Kamel Afifi 11/9/2024 3 Preparation of bone tissue for microscopic examination: ‫بحث الصور عن‬ decalcified bone ‫نتيجة‬ labeled ▪Decalcified sections: the bone is treated with dilute acid solution (5% nitric acid). Then, sections are prepared & stained in ordinary manner. Cells & organic components are preserved. ▪Ground section: grinding a thin piece of bone until it become transparent. Sections are obtained & examined with the microscope. No stains, the bone cells are destroyed, so lacunae & canaliculi appear black due to the entrapped air. Prof Dr Omayma Kamel Afifi 11/9/2024 4 2  11/9/2024 Structure of bone tissue Bone is composed of: a) Bone cells (4 types; origin, site, L/M, E/M, function of each cell) 1-Osteogenic (quiescent stem cells) 2-Osteoblast (bone formation) 3-Osteocyte (mature cells) 4-Osteoclast (bone resorption) b) Extracellular calcified matrix: Collagen fibers (type I) & Ground substance. Covered externally by periosteum & Lined by endosteum Prof Dr Omayma Kamel Afifi 11/9/2024 5 Periosteum Endosteum External covering, formed of Lines all internal surfaces or two layers: bone cavities within the bone 1.Outer fibrous: dense CT Single cellular layer: osteogenic 2.Inner cellular: osteogenic cells cells & & osteoblasts. Image result for periosteum and endosteum Functions: both are important for bone nutrition, growth & repair. Prof Dr Omayma Kamel Afifi 11/9/2024 6 3  11/9/2024 Bone matrix: (extracellular matrix) Inorganic Components: ▪ About 50-60% of the dry weight of bone. ▪ Composed mainly of calcium salts (ca hydroxyapatite) & phosphate. Organic Components: ▪ About 40-50% of the dry weight of bone. Composed of: - Collagen fibers type I in the form of collagen bundles. - Ground substance: a.Glycosaminoglycans [GAGs]. B.Proteoglycans. c. Glycoproteins. The matrix acidophilic (collagen) in Hx &E sections & it is PAS +ve. Prof Dr Omayma Kamel Afifi 11/9/2024 7 Bone cells Prof Dr Omayma Kamel Afifi 11/9/2024 8 4  11/9/2024 1- Osteogenic cells Origin Mesenchyme (UMC( Site Osteogenic layer of periosteum & endosteum L/M Small spindle-shaped, with pale nuclei & basophilic cytoplasm E/M Abundant free ribosomes, mitochondria, RER. Function Stem cell; can undergo mitotic division & differentiate into osteoblasts Prof Dr Omayma Kamel Afifi 11/9/2024 9 2- Osteoblasts Origin Osteogenic cells Site On the surfaces of bone (like arrangement of simple cuboidal) L/M Active, deeply basophilic cytoplasm with -ve Golgi image, large, pale rounded nucleus, very thin cytoplasmic processes extending to those of adjacent cells E/M, Actively secreting cells (abundant rER, well-developed Golgi, numerous secretory vesicles, many ribosomes & mitochondria. nucleus with extended chromatin), Function Synthesis of the organic bone matrix, secrete alkaline phosphatase enzyme which precipitate ca salts in the matrix Prof Dr Omayma Kamel Afifi 11/9/2024 10 5  11/9/2024 3-Osteocytes (mature) Origin Osteoblasts when surround themselves with the matrix. Site Each osteocyte are imprisoned in a lacuna within calcified bony matrix, one cell in each lacuna, processes in canaliculi to contact the processes of adjacent cells L/M Smaller than osteoblasts, less basophilic, flattened & deeply stained nucleus E/M Poor in organelles; scanty RER, & Golgi, central nucleus with condensed chromatin, processes joined inside canaliculi by gap junctions Function Maintain the bone Matrix Prof Dr Omayma Kamel Afifi 11/9/2024 11 4-Osteoclasts Origin Fusion of blood monocytes Site Bone surface in shallow depressions (Howship's lacunae) L/M Giant motile branched cells, multinucleated (up to 50 nuclei), acidophilic cytoplasm, surface facing bone is irregular (ruffled or striated border). E/M Many zones; ruffled border (cell membrane enfolding), clear zone (actin filaments), vesicular zone (endocytic vesicles, lysosomes & vacuoles, basal zone (organelles & multiple nuclei) Prof Dr Omayma Kamel Afifi Function 11/9/2024 Bone resorption & remodeling 12 6  11/9/2024 Prof Dr Omayma Kamel Afifi 11/9/2024 13 Microscopic types of bone 1.Spongy (cancellous) bone: irregular bone trabeculae enclosing spaces filled with bone marrow. 2.Compact bone: solid dense mass of bone without cavities. Both types are present in every bone, in varying distribution & amount Prof Dr Omayma Kamel Afifi 11/9/2024 14 7  11/9/2024 Microscopic structure of decalcified compact bone: e.g. the diaphysis of long bones Composed of four lamellar systems: 1-Outer circumferential lamellae: just beneath the periosteum 2-Inner circumferential lamellae: between endosteum & the marrow cavity 3-Haversian system (osteon): parallel to the long axis of bone 4-Interstitial lamellae: in-between Haversian systems. Prof Dr Omayma Kamel Afifi 11/9/2024 15 Prof Dr Omayma Kamel Afifi 11/9/2024 16 8  11/9/2024 Haversian system (osteon): - Concentric lamellae of regularly arranged collagenous fibers around a vascular Haversian canal. - Each canal is lined with endosteum (osteoblasts & osteogenic cells) & contains blood vessels & nerves with C.T. - The canal run parallel to the long axis of the bone & connected with each other, periosteum & endosteum by Volkmann's canals. - Volkmann's canals are, transverse or oblique, lined with endosteum & contain blood vessel, nerves & C.T. Prof Dr Omayma Kamel Afifi 11/9/2024 17 Microscopic structure of spongy (cancellous) bone: 1- Bone trabeculae (irregular bone lamellae that branch & unit with one another enclosing marrow spaces & scattered osteocytes between these lamellae). No Haversian system. 2- Bone marrow cavities: multiple between the bone trabeculae. Prof Dr Omayma Kamel Afifi 11/9/2024 18 9  11/9/2024 Types according to development & healing Primary (1ry) (Immature; woven) Secondary (2ry) (mature or lamellar) First bone to appear in development, fracture & repair Replace the 1ry bone Temporary, replaced by 2ry, except in few areas Permanent (e.g. near sutures). Usually in adults. a) More Cells (osteocytes). a)More calcified (more stronger) b) Irregular Collagen. b)Regular collagen c) Less Calcium (Less mineral). c)Evenly acidophilic d) More proteoglycans & glycoproteins (the d)Organized to compact or spongy matrix is unevenly stained, with areas of basophilia) 19 Disturbance of the normal balance between Bone formation (by osteoblasts) & Bone resorption (by osteoclasts) resulting in: Osteopetrosis (too much bone) Osteoporosis (low bone density) Genetic disease (lack of a ruffled Aging disease; more rapidly in border of osteoclasts) women after menopause Bone resorption is defective Bone formation is defective The bones are dense, heavy Bone density decreases Prevents enlargement of marrow Fragile bone with an increased cavities, leading to hematological susceptibility to fracture failure Prof Dr Omayma Kamel Afifi 20 10  11/9/2024 Cartilage Bone 1.Soft, elastic, flexible 1.Hard, inelastic & tough 2.Nonvascular 2.Vascular 3.Two main cell` types: chondroblast & 3.Four cell` types: osteogenic, osteoblast, chondrocytes osteocyte & osteoclast 4.Homogenous non-lamellar matrix 4.Lamellar matrix 5.Organic matrix 5.Organic & nonorganic matrix 6.No calcium 6.Has calcium 7.Each lacuna has more than one cells up 7.Each lacuna has one cell to 8 8.No canaliculi 8.Has canaliculi 9.Haversian & Volkman canals are absent 9.Haversian & volkman canals are present 10.Three types (hyaline, elastic & (in compact) fibrocartilage) 10.Two types (compact & spongy), or primary & secondary Prof Dr Omayma Kamel Afifi 11/9/2024 21 Volkman's canals are characterized by which of the following? A- Contains no blood vessels. B- Are at the centre of the osteon. C- Communicate with Haversian canals. D- Are arranged parallel to the bone surface Osteoclasts are characterized by which of the following? A- Derived from fusion of monocytes. B- Bone forming cells. C- Large cells with a single kidney shaped nucleus. D-Present in the bone matrix 22 11  11/9/2024 Osteoblasts synthesize the collagen fibers, mainly of type: A- I B- II C- III D- IV Which of the following cells is joined with each other by gap junctions inside canaliculi? A.Osteoblasts B.Osteocytes C.Osteoclasts D.Osteogenic Thank You Enumerate types of bone cells? Mention three differences between cartilage and bone? 23 12