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Histo – bone
This document provides an overview of bone histology. It defines bone as a mineralized connective tissue composed of bone matrix and three cell types: osteoblasts, osteocytes, and osteoclasts. It describes the microscopic structure of compact and spongy bone, including osteons, central canals, lamellae, and trabeculae. It explains the functions of osteoblasts in bone formation, osteoclasts in bone resorption, and osteocytes in bone maintenance. Finally, it discusses the periosteum and endosteum, which cover the external and internal bone surfaces and provide nutrition and new osteoblasts.
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Histo – bone
- 1. Histology of theBone By: Dr Mohammed Faez
- 2. Objective of TheLecture • 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 isa 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 isa 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 • Protectsvital organs • Supports soft tissue • Movement • Mineral storage • Blood cell production
- 6. Microscopic structure of compactbone • 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 compactbone Osteon System: • A central (Haversian) canal with concentric rings (lamellae) of bone matrix running lengthwise. • Very strong!
- 8. Microscopic structure of compactbone • 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.
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- 10. Osteon Central Canal w/ bloodvessels, nerves Lacunae w/ bone cells
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- 13. Spongy Bone • Spongybone 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.
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- 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 • Ifmineral removed, bone is too bendable • If collagen removed, bone is too brittle
- 17. Bone Cells 1. Osteoblasts:Bone generating cells “B” means building 2. Osteocytes: Mature bone cells, spider shaped and maintain bone tissue 3. Osteoclasts: Bone destroying cells “C” means chewing
- 18. Osteoblasts • Osteoblasts are responsiblefor 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 areexclusively 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.
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- 21. Osteocytes • Osteocytes, which derivefrom 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
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- 24. Osteoclasts • Osteoclasts arevery 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.
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- 30. Periosteum • It consistsof 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.
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- 32. Endosteum • It linesall 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.
- 33. 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.
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