Bone histology.pptx

Bone both transverse and longitudinal sections are described in detail.

1. Histology of bone Dr. P. Christabel Divya

2. Introduction Solid support for the body Protects vital organs such as those in the cranial and thoracic cavities Harbors cavities containing bone marrow where blood cells are formed Reservoir of calcium, phosphorous and other ions that can be released or stored in a controlled fashion to maintain constant concentration in body fluids

3. Constituents Specialized connective tissue Cells Osteoprogenitor cells Osteoblasts Osteocytes Osteoclasts Calcified extracellular matrix Organic matter Fibres – Type 1 collagen Ground substances – Proteoglycans ( aggregcan ) and Glycoproteins ( Osteonectin ) and water Inorganic material – 50% of dry weight Calcium hydroxyapatite Other ions - Bicarbonate, citrate, magnesium, potassium, sodium ions

4. Bone membranes Bones are lined on both internal and external surfaces by layer of connective tissue containing osteoprogenitor cells Endosteum – On the internal surface surrounding the marrow cavity Periosteum – On the external surface

5. Bone Cells Osteoprogenitor cells Osteoblasts Osteocytes Osteoclasts

6. Osteoprogenitor cells Stem cells of mesenchymal origin Resembles fibroblast in appearance Located over the bone surfaces (on both the periosteal and endosteal aspects) Can proliferate and convert themselves into osteoblasts

7. Osteoblast Bone forming cell Cuboidal to columnar shape with basophilic cytoplasm Located at the surfaces of bone matrix, usually side by side in a layer Synthesize and secrete the organic components of bone matrix, including type I collagen fibres , proteoglycans and glycoproteins ( osteonectin )

8. Osteoblast contd Secrete matrix components at the cell surface in contact with the existing bone matrix, producing a layer of new material called osteoid (but not yet calcified) between osteoblast layer and pre existing bone surface Completed by subsequent deposition of calcium salts into the newly formed matrix

9. Osteocytes Cells of mature bone Lie in the lacunae of bone that lies in between the successive lamellae and are regularly spaced through out the mineralized matrix Osteoblasts that have become imprisoned in the matrix during bone formation and differentiate further as osteocyte

10. Osteocytes contd In the transistion from osteoblast to osteocyte, cells extend many long dendritic process arising from osteocytes Establishes contacts with other osteocytes and with bone lining cells present on the surface of bone Maintain bone matrix and their death is followed by matrix resorption Additional role in calcium homeostasis

11. Osteoclasts Bone removing cells Very large motile cells with multiple nuclei, the surface of the cell is folded into irregular projections (Ruffled border) Found in relation to surface where bone removal is taking place, lies within enzymatically etched depression or cavities in the matrix (Resorption bays or Howship’s lacunae) Removal of bone by osteoclast involves demineralization and removal of matrix

12. Periosteum External surface of any bone Consists of two layers Outer Inner Outer layer – Fibrous layer Inner layer – Cellular layer. Contains osteoprogenitor cells (Osteogenic layer) Richly supplied with blood.

13. Functions of periosteum Provides a medium through which muscles, tendons and ligaments are attached to bone. Fibers of the tendon continue into the outer layers of bone as perforating fibers of sharpey Performs a nutritive function because of the blood vessels supplying it

14. Functions of periosteum contd Can form bone when required because of the presence of osteoprogenitor cells in its deeper layer Limiting membrane that prevents bone tissue from spilling out into neighbouring tissues. Ridges and tubercles are formed on the surface where a tendon pulls upon the periosteum

15. Types of bone Based on the gross appearance Compact bone (cortical) Cancellous bone (spongy) Compact – Dense area near the surface (80% of mass) Cancellous – Deeper areas with numerous interconnecting cavities (20% of mass)

16. In long bones Epiphysis – spongy bone are covered by a thin layer of compact bone Diaphysis – Composed of contact bone with a thin region of spongy bone on the inner surface around the central marrow cavity Short bones Cores of spongy bone surrounded by compact bone Flat bone Have two layers of compact bone called plates, separated by a thick layer of spongy bone called diploe

17. Types of bone contd Based on the microscopic examination Lamellar bone – Mature Woven bone - Immature

18. Lamellar bone Made up of layers or lamellae Lamellus – thin plate of bone consisting of collagen fibers and mineral salts that are deposited in a gelatinous ground substance Mainly depends on the arrangement of collagen fibers Fibers of one lamellus run parallel to each other but those of adjoining lamellae runs at perpendicular direction

19. Woven bone Newly formed bone does not have a lamellar structure Collagen fibers present in bundles that appear to run randomly in different directions interlacing with each other Later replaced by lamellar bone

20. Micro structure of bone Lamellae are organized around a central canal (Haversian canal) and parallel to each other Osteon (Haversian system) – Complex of concentric lamellae surrounding a small central canal that contains nerves, blood vessels and loose connective tissue Between successive lamellae are lacunae, each with one osteocyte, interconnected by canaliculi containing the cells dendritic process Receives nutrients and oxygen from the microvasculature in the central canal Outer boundary of each osteon is cement line, which is a more collagen rich layer

21. Micro structure of bone Osteons arranged as long cylinder parallel to the long axis of the diaphysis Central canal surrounded by 4-10 concentric lamellae Central canal communicate with marrow cavity & periosteum and with one another through perforating channels (or Volkmann canals) Scattered among the intact osteon, numerous irregular shaped groups of parallel lamellae called interstitial lamellae Lamellae remaining from osteons partially destroyed by osteoclast during growth and remodeling of bone

22. Micro structure of bone External circumferential lamellae – located immediately beneath the periosteum Inner circumferential lamellae – Located around the marrow cavity

23. Compact bone TS Ring like osteons (or haversian systems) At the center of each osteon, there is haversian canal Around the canal, there are concentric lamellae of bone amongst which there are small spaces called lacunae (containing osteocytes) Delicate canaliculi radiate from the lacunae; these contain cytoplasmic processes of osteocytes

24. Compact bone TS Interstitial lamellae fill intervals between haversian systems Near the surface of compact bone, the lamellae are arranged in a parallel manner. These are circumferential lamellae Volkmann’s canal interconnecting the adjacent Haversian canal may be seen

25. Compact bone LS Volkmann’s canal connecting Haversian canal is seen Osteocytes within lacunae is seen

26. The end