Histo – bone

1. Histology of the Bone By: Dr Mohammed Faez

2. Objective of The Lecture To know about definition of the bone. To master the basic structure of the bone. To know about bone matrix and bone cells. Illustrate and differentiate the three type of bone cells. To know about the periosteum & endosteum.

3. Bone Bone is a dense, semirigid , porous, calcified connective tissue forming the major portion of the skeleton. It consists of a dense organic matrix and an inorganic, mineral component.

4. Bone Bone is a specialized connective tissue composed of intercellular calcified material, the bone matrix , and three cell types: osteocytes , osteoblasts and osteoclasts All bones are lined on both internal and external surfaces by layers of tissue containing osteogenic cells endosteum on the internal surface and periosteum on the external surface.

5. Bone Functions Protects vital organs Supports soft tissue Movement Mineral storage Blood cell production

6. Microscopic structure of compact bone The structural unit of Compact bone is the osteon,or haversian system. Each osteon Is an elongated cylinder Oriented parallel to the Long axis of the bone.

7. Microscopic structure of compact bone Osteon System : A central ( Haversian) canal with concentric rings ( lamellae ) of bone matrix running lengthwise. Very strong!

8. Microscopic structure of compact bone Central, or haversian canal carries blood vessels and nerves to all areas of the bone. Canaliculi tiny canals that radiate outward from the central canals to each lacunae space. Volkmann’s Canals : canals that run at right angles to the central canals and perforate the shaft of the bone.

9. Microscopic structure of compact bone

10. Osteon Central Canal w/ blood vessels, nerves Lacunae w/ bone cells

11. Compact bone structure

12. Compact bone structure

13. Spongy Bone Spongy bone contains trabeculae and spicules giving it a honeycomb appearance. Trabeculae : are irregularly arranged and contain lamellae and osteocytes , but contain no osteons as they receive nutrients from the marrow tissue.

14. Spongy bone histology

15. Bone Matrix 25% Water 25% Protein or organic matrix 95% Collagen Fibers 5% Chondroitin Sulfate 50% Crystalized Mineral Salts Hydroxyapatite (Calcium Phosphate) Other substances: Lead, Gold, Strontium, Plutonium, etc. Combination provides strength and rigidity Laid down by osteoblasts

16. Bone Matrix If mineral removed, bone is too bendable If collagen removed, bone is too brittle

17. Bone Cells Osteoblasts : Bone generating cells “B” means building Osteocytes : Mature bone cells, spider shaped and maintain bone tissue Osteoclasts : Bone destroying cells “C” means chewing

18. Osteoblasts Osteoblasts are responsible for the synthesis of the organic components of bone matrix (type I collagen, proteoglycans , and glycoproteins ). Osteoblasts depends on deposition of the inorganic components of bone.

19. Osteoblasts Osteoblasts are exclusively located at the surfaces of bone tissue, side by side, in a way that resembles simple epithelium. When they are actively engaged in matrix synthesis, osteoblasts have a cuboidal to columnar shape and basophilic cytoplasm. When their synthesizing activity declines, they flatten, and cytoplasmic basophilia declines.

20. Osteoblasts

21. Osteocytes Osteocytes , which derive from osteoblasts , lie in the lacunae situated between lamellae of matrix. Only one osteocyte is found in each lacuna. Lacunae : spaces occupied by osteocyte cell body

22. Osteocytes

23. Osteocytes

24. Osteoclasts Osteoclasts are very large and branched motile cells. Dilated portions of the cell body contain from 5 to 50 (or more) nuclei. Osteoclasts are derived from the mononucleated cells; (engulf bony material). Active osteoblasts stimulate osteoclast activity .

25. Osteoclasts Resorption of bone Ruffled border: where cell membrane borders bone and resorption is taking place. H ions pumped across membrane, acid forms, eats away bone. Release enzymes that digest the bone.

26. Osteoclasts

27. Bone Resorption

28. Periosteum It consists of an outer layer of collagen fibers and fibroblasts. Bundles of periosteal collagen fibers, called Sharpey's fibers , penetrate the bone matrix, binding the periosteum to bone.

29. Periosteum

30. Endosteum It lines all internal cavities within the bone and is composed of a single layer of flattened osteoprogenitor cells and a very small amount of connective tissue. The endosteum is therefore considerably thinner than the periosteum.

31. Periosteum & Endosteum The principal functions of periosteum and endosteum are nutrition of osseous tissue and provision of a continuous supply of new osteoblasts for repair or growth of bone.

32. Periosteum & Endosteum