Basics of the bone histology
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This document summarizes bone histology and cellular biology. It describes that bone is composed of bone cells, bone matrix, periosteum, and endosteum. The main bone cells are osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts. Osteoblasts form bone matrix and regulate osteoclasts, osteocytes maintain bone, and osteoclasts resorb bone. Bone formation occurs through either intramembranous or endochondral ossification. Cortical bone consists of tightly packed osteons, while cancellous bone is less dense and more elastic.
Basics of the bone histology
- 1. Bone Hisotology By Mohamed Attia MD, Ph.D Azhar Medical School 2020 Mohamed Attia MD, Ph.D 1
- 2. Bone is formed of Bone cells Bone matrix Perisoteum Endosteum Mohamed Attia MD, Ph.D 2
- 3. Bone cells Osteoprogenitor cells Osteoblast Osteocyte Osteoclast Mohamed Attia MD, Ph.D 3
- 4. Bone matrix Organic component 1- Collagenous fibers : type one collagen 2- Ground substance Mucopolysaccarides, osteocalcin, osteopontin In organic component Ca, Phosphorus form (OH) apatite crystals Mohamed Attia MD, Ph.D 4
- 5. Histologic features of bone ■ Types • Normal bone: lamellar or mature; either cortical or cancellous • Immature and pathologic bone: woven; more random, more osteocytes, increased turnover, weaker Mohamed Attia MD, Ph.D 5
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- 7. Cortical (compact) bone • Constitutes 80% of the skeleton • Consists of tightly packed osteons or haversian systems • Connected by haversian (or Volkmann) canals • Contains arterioles, venules, capillaries, nerves, possibly lymphatic channels Mohamed Attia MD, Ph.D 7
- 8. • Interstitial lamellae: between osteons • Fibrils connect lamellae but do not cross cement lines. • Cement lines define the outer border of an osteon. • Bone resorption has stopped and new bone formation has begun. • Nutrition provided by intraosseous circulation through canals and canaliculi (cell processes of osteocytes) • Characterized by slow turnover rate, higher Young’s modulus of elasticity, more stiffness Mohamed Attia MD, Ph.D 8
- 9. Cancellous bone (spongy or trabecular bone) • Less dense, more remodeling according to lines of stress (Wolff’s law) • Characterized by high turnover rate, smaller Young’s modulus, more elasticity Mohamed Attia MD, Ph.D 9
- 10. Cellular biology I- Osteoprogenitor cells Falt cells. Falt nucleus, pale basophilic cytoplasm Arises from pericytes around the caplillaries Mohamed Attia MD, Ph.D 10
- 11. Cellular biology Osteoblasts • Appear as cuboid cells aligned in layers along immature osteoid • Derived from undifferentiated mesenchymal stem cells • Have more endoplasmic reticulum, Golgi apparatus, and mitochondria than do other cells (for synthesis and secretion of matrix) Mohamed Attia MD, Ph.D 11
- 12. • RUNX2 is a multifunctional transcription factor that directs mesenchymal cells to the osteoblast lineage. • Bone surfaces lined by more differentiated, metabolically active cells • “Entrapped cells”: less active cells in “resting regions”; maintain the ionic milieu of bone • Disruption of the active lining cell layer activates entrapped cells. Osteoblast has two main functions: • Form bone • Regulate osteoclastic activityMohamed Attia MD, Ph.D 12
- 13. • Osteoblasts produce the following: • Alkaline phosphatase • Osteocalcin (stimulated by 1,25 dihydroxyvitamin D) • Type I collagen • Bone sialoprotein • Receptor activator of nuclear factor (NF)-κB ligand (RANKL) • Osteoprotegrin—binds RANKL to limit its activity Mohamed Attia MD, Ph.D 13
- 14. Osteoblast activity is stimulated by intermittent (pulsatile) exposure to parathyroid hormone (PTH) Osteoblast activity is inhibited by tumor necrosis factor (TNF)-α • Wnts are proteins that promote osteoblast survival and proliferation. • Deficient wnts causes osteopenia; excessive wnt expression causes high bone mass. Mohamed Attia MD, Ph.D 14
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- 18. Osteocytes • Maintain bone • Constitute 90% of the cells in the mature skeleton • Former osteoblasts surrounded by newly formed matrix High nucleus/cytoplasm ratio Long interconnecting cytoplasmic processes projecting through the canaliculi Mohamed Attia MD, Ph.D 18
- 19. Less active in matrix production than are osteoblasts Important for control of extracellular calcium and phosphorus concentration Directly stimulated by calcitonin, inhibited by PTH Sclerostin secreted by osteocytes helps negative feedback on osteoblasts’ bone deposition Mohamed Attia MD, Ph.D 19
- 20. Osteoclasts Formation • Multinucleated irregular giant cells • Derived from hematopoietic cells in macrophage lineage • Monocyte progenitors form giant cells by fusion Mohamed Attia MD, Ph.D 20
- 21. Osteoclast Function Resorb bone Synthesize tartrate-resistant acid phosphate Bind to bone surfaces through cell attachment (anchoring) proteins Mohamed Attia MD, Ph.D 21
- 22. Bone resorbtion which occurs both normally and in certain conditions including multiple myeloma and metastatic bone disease • Possess a ruffled (“brush”) border and surrounding clear zone • Border consists of plasma membrane enfoldings that increase surface area for resorption. Bone resorption occurs in depressions: Howship lacunae. • Formation and resorption are linked (“coupled”). • Resorption occurs more rapidly Mohamed Attia MD, Ph.D 22
- 23. Osteoclasts • Produce hydrogen ions through carbonic anhydrase • Lower PH • Increase solubility of hydroxyapatite crystals • Organic matrix then removed by proteolytic digestion through activity of the lysosomal enzyme cathepsin K Mohamed Attia MD, Ph.D 23
- 24. Control and function of the osteoclast. OPG, Osteoprotegerin; PTH, parathyroid hormone; RANKL, receptor activator of nuclear factor κB ligand; Vit, vitamin. Mohamed Attia MD, Ph.D 24
- 25. Osteoblasts (and tumor cells) express RANKL which acts as follows: • Binds to receptors on osteoclasts • Stimulates differentiation into mature osteoclasts • Increases bone resorption • Inhibited by osteoprotegerin binding to RANKL Mohamed Attia MD, Ph.D 25
- 26. Bisphosphonates • Inhibit osteoclastic bone resorption—direct anabolic effect on bone , so it is used for the treating Osteoporosis Mohamed Attia MD, Ph.D 26
- 27. Tissues surrounding bone Periosteum : Outer fibrous layer : Connective tissue membrane covers bone. • More highly developed in children • is less cellular and is contiguous with joint capsules. Protection, nutrition, attachment of tendons, ligaments, muscles Inner cellular layer , or cambium, is loose and vascular and contains cells capable of becoming osteoblasts. • Cells enlarge the diameter of bone during growth and form periosteal callus during fracture healing. Mohamed Attia MD, Ph.D 27
- 28. Endosteum It lines the bone marrow cavity , Mohamed Attia MD, Ph.D 28
- 29. T.S in Decalcified Cortical bone Mohamed Attia MD, Ph.D 29
- 30. Cortical bone Mohamed Attia MD, Ph.D 30
- 31. Cancellous bone Mohamed Attia MD, Ph.D 31
- 32. Development of the bone Mohamed Attia MD, Ph.D 32
- 33. 1- Intramembranous ossification Mesenchymal CT is converted to bone without passing through cartilagenous stage , occur in flat, short, irregular bone Mohamed Attia MD, Ph.D 33
- 34. 2- Endochondral ossification Mohamed Attia MD, Ph.D 34
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- 36. Thank you If there be any queries, please do not hesitate to contact me orthobiologist@gmail.com 010-2728-3050 Mohamed Attia MD, Ph.D 36