Bone tissue ppt.pptx

Bone tissue for Biomedical students

1. Outlines Introduction to Bone tissue Functions Parts of bone tissue Components Cells Classifications Compact bone Spongy Bone Formation HISTOLOGY ASSIGNMENT ON BONE TISSUE prepared by : A manuel Ibrahim Submitted to:Mr Tilahun A (Asst pro Anatomy) Date of presentation April/2023

2. OUTLINES Introduction to Bone tissue Components of bone Functions of bone Cells of bone tissue Bone matrix Classifications Bone formation Bone fracture Bone Remodeling

3. Introduction to Bone tissue Bone is a connective tissue characterized by a mineralized extracellular matrix . The mineralization of the matrix of bone sets bone different from other connective tissues and results in an incredibly tough structure that can support and protect. The mineral is calcium phosphate in the form of hydroxyapatite crystals [Ca10(PO4)6(OH)2].

4. Bone matrix contains mainly type I collagen along with other matrix . The major structural component of bone matrix is type I collagen and , to a lesser extent , type V collagen . Trace amounts of other types such as type III , XI , and XIII collagens have also been found in the matrix. All collagen molecules constitute about 90% of the total weight of the bone matrix proteins .

5. The bone also contains other ( non collagenous proteins ) that constitute the ground substance of bone. As a minor component of bone, constituting only 10% of the total weight of bone matrix proteins . T hey are essential to bone development , growth , remodeling , and repair . In order to create bone tissue, both the collagen and the ground substance undergo mineralization.

6. Components of Bone Bone membranes Periosteum & Endosteum Cells Osteoblast - Osteocyte – Osteoclast Extra cellular matrix (ECM) Fibres (95%) - collagen fibre Type1 Noncollagenous proteins Ground substance (5%)

7. Periosteum Dense CT surrounding bone important in bone repair Outer fibrous layer superficial layer is more vascular and receives periosteal vessels. Deep layer  is a fibro-elastic. Inner layer ( osteogenic layer ) with bone cells, precursors, and blood vessels .

8. Endosteum Thin layer of CT lining inner surface of bone facing marrow consists of a layer of flattened osteoprogenitor cells and a type-III collagenous fibers. classified into three types based on their site: Cortical endosteum : lining the bone marrow cavity Osteon endosteum : lining the osteons mainly contains nerves and blood vessels. Trabecular endosteum : Lines the trabecula near the developing part of the bone.

9. F our main groups of noncollagenous proteins Proteoglycan macromolecules Comprise a core protein with a variety of covalently linked glycosaminoglycan side chains . Key ingredients include hyaluronan, chondroitin sulphite, and keratan sulfate . They contribute to the compressive strength of bone .

10. 2. Multiadhesive glycoproteins Are responsible for attachment of bone cells and collagen fibers to the mineralized ground substance. One of the more important glycoproteins is osteonectin , which functions as a binding agent between the collagen and hydroxyapatite crystals.

11. Podoplanin , which is produced exclusively by osteocytes in response to mechanical stress. protects against increases in osteoclast formation and activity. Dentin matrix protein , which is critical for bone matrix mineralization . Multiadhesive glycoproteins cont…

12. One of the more significant glycoproteins is osteonectin, which acts as a binder between collagen and hydroxyapatite crystals . Other key glycoproteins include osteopontin, which facilitates cell attachment to bone matrix. Osteonectin which mediates cell attachment and initiates calcium phosphate formation during the mineralization process.

13. 3 . Bone-specific , vitamin K–dependent proteins Containing:- osteocalcin , which draws calcium from the bloodstream and attracts and encourages osteoclasts during bone remodeling . protein S , which assists in the removal of cells undergoing apoptosis. matrix Gla -protein (MGP ), which participates in the development of vascular calcifications .

14. 4. Growth factors and cytokines S mall regulatory proteins such as insulin-like growth factors ( IGFs ) tumor necrosis factor ( TNF - ) transforming growth factor ( TGF - ) platelet-derived growth factors ( PDGFs ) bone morphogenic proteins ( BMPs )

15. Growth factors and cytokines cont… sclerostin ( BMP antagonist ) interleukins ( IL-1,IL-6 ). N.B ; containing osteocalcin, which draws calcium from the bloodstream and attracts and encourages osteoclasts during bone remodeling . Cytokines;-are small secreted proteins released by cells have a specific effect on the interaction and communications between cells

16. Functions of bone tissue Locomotion Support and protects internal organs. Storage site for calcium( 99%) and phosphate( 85%) . Regulates blood calcium level. Blood cell production . ( harbors bone marrow)

17. CELLS OF BONE TISSUE Five designated cell types are associated with bone tissue: osteoprogenitor cells osteoblasts osteocytes bone-lining cells osteoclasts .

18. CELLS cont… With the exception of the osteoclast, all of these cells can be thought of as distinct varieties of the same basic cell type. Each undergoes transformation from a less mature form to a more mature form in relation to functional activity (growth of bone)

19. Osteoprogenitor cells As a pleuripotent stem cell, mesenchymal stem cells in the bone marrow have the capacity to develop into a wide variety of cell types. In Adults found in the deepest layer of periosteum and endosteum . Osteogenic – gives rise to osteoblasts where ever there is need for bone formation.

20. Osteoblast Drived from osteoprogenitor cells (osteoblast precursor cells) . found Lining growing surface of bone. Roughly cuboidal . Nucleus eccentric , ovoid . Cytoplasm deeply basophilic (RER)

21. Osteoblast cont’ Electron microscope reveal typical protien secreting cells ( increased in Golgi complexes ). Form bone tissue = synthesis and secretion of osteoids (collagen fibers and ground substances ). Only 10% to 20% of osteoblasts differentiate into osteocytes.

22. Osteoblast cont’ Others transform into inactive cells and become either periosteal or endosteal bone-lining cells majority of osteoblasts undergo apoptosis . The cytoplasm of the osteoblast is markedly basophilic Golgi apparatus sometimes observed as a clear area adjacent to the nucleus.

23. Histologic slide of osteoblast

24. Osteocytes The osteocyte is the mature bone cell enclosed by bone matrix that was previously secreted as an osteoblast. formed from osteoblast When completely surrounded by osteoid or bone matrix , the osteoblast is referred to as an osteocyte smaller Less basophilic cytoplasm

25. Osteocytes Major cell type oval in long axis Prominent nucleus Cell trapped in a space in the matrix = lacunae Maintains bone tissue. The natural lifespan of osteocytes in humans is estimated to be about 10 to 20 years .

26. Histologic slide of Osteocyte

27. Osteoclasts Bone removing cells Large cells 20-100um Oval cells with multiple nucleii 15-20 or > Ruffled border Found where active bone resorption , remodeling and repair takes place. Cells are found in pits –resorption bays / lacunae of Howship ( As a result of osteoclast activity). Fxn - resorption and destruction of bone matrix.

28. Histologic slide of osteoclast

29. Histological slide of bone tissue Key:- CM, zone of calcified matrix C, calcified cartilage EB, endochondral bone HC,hypertrophic cartilage M, marrow Ob,osteoblast Oc , osteocyte Ocl , osteoclast PC, zone of proliferating cartilage RC, zone of reserve cartilage arrow, ruffled border of osteoclast R, zone of resorption

30. Bone-lining cells Derived from osteoblasts and cover bone that is not remodeling . In sites where remodeling is not occurring, the bone surface is covered by a layer of flat cells with attenuated cytoplasm and a paucity of organelles beyond the perinuclear region . These cells are designated simply as bone-lining cells.

31. Bone-lining cells on external bone surfaces are called periosteal cells, and those lining internal bone surfaces are often called endosteal cells. Gap junctions are present where the bone-lining cell processes contact one another. Function in the maintenance and nutritional support of the osteocytes. Regulate the movement of calcium and phosphate into and out of the bone. Bone-lining cells cont ’

32. Extracellular matrix surrounds widely separated cells 15% water 30% collagen fibers (organic materials) 55% crystallized mineral (inorganic materials)

33. Components of bone matrix INORGANIC 2/3 of bone matrix 65% of dry bone weight Ions – calcium , phosphate , magnesium , carbonate , Hydroxyl , chloride , citrate , Na+,k + Salts – crystals of hydroxyappetite Ca3( po =)6(oh)2 Calcium phosphate Ca3(PO4)2 calcium hydroxide Ca(OH)2

34. organic 1/3 of bone matrix 35% of dry bone weight ground substance & fibers Ground substance binds to calcium ions = mineralization of bone. -Glycosaminoglycans -Proteoglycans -Glycoprotiens -Chondrotin sulphate -Phospholipids -Phosphoprotiens -water

35. FIBERS Collagen Tyepe I Arranged in parellel layers Synthesized by osteoblasts Osteoids = (ground substance + collagen fibers) minus minerals.

36. Classification of bone Based on Histology compact bone spongy /cancellous/ Trabecular bone Based on Developmental orgin Membraneous cartilaginous Based on Maturity Non-lamellar bone / Woven / lmmature Lamellar bone/Mature

37. LAMELLAR BONE Adult bone is made up of layers called lamellae thus called lamellar bone. A lamella is thin plate of bone made up of ground substances with collagen fibers in it and mineral salts . Between each layers there are flat spaces called lacunae . Each lacuna contains one osteocyte .

38. LAMELLAR BONE CONT’ spreading out from each lacuna are fine canaliculi that communicates with those from other lacunae. In the canaliculi are fine cytoplasmic processess of osteocytes. Collagen fibers in one lamella run parallel to each other, but in adjoining lamellae they may be in different directions.

39. Woven bone It is the first formed bone in prenatal life . Does not have a clear lamellar structure . Ground substance , collagen fibers , cells , minerals are present. Collagen fibers are in different directions in one lamellar, they are interlaced with each other ‘ woven ’

40. Woven cont’ Mechanically it is weak Replaced by lamellar bone at a later date. Present in adulthood where new bone is forming, reparing and remodeling of bone is taking place.

41. SPONGY BONE Made up of meshwork of bony rods called trabeculae. Trabeculae Branching, anastmosing and curved. Have lamellae with lacunae (with osteocytes) Enclose within the trabeculae are spaces filled with haemopoetic tissu e/bone marrow. Trabeculae are covered extremely by endosteum . No haversian system( osteon ) .

42. Microscopic structures of spongy bone

43. COMPACT BONE Consists of layers called lamella , made up of collagen fibers embedded in ground substances which is mineralized. There are three types of lamellae Circumferential lamellae- outer and inner (inside periosteum and endosteum) Concentric lamellae (arround haversian canal) Interstitial lamellae (b/n haversians system)

44. Concentric lamellae (Oteon or Haversian System) Long, sometimes bifurcated , 100-250 μm diameter Cylinderical, generally running parallel to the long axis of the diaphysis. Contains 5-20 concentric lamellae around a Haversian canal that a re interconnected by perforating ( Volkmann’s) canals . Compact bone cont ’

45. Has blood vessels, nerves, & endosteum In each osteon, collagen bundles run parallel within a lamella, but perpendicular to those of adjacent lamellae Each osteon is bounded by cementing line composed mostly of calcified ground substance with a scant amount of collagen fibres. Compact bone cont’

46. Circumferential lamellae Outer circumferential lamellae Contain Sharpey’s fibres . Inner circumferential lamellae Not as extensive as the outer circumferential lamellae. Interstitial lamellae Irregular lamellae found between the osteons . Outlined by cement lines. Are remnants of osteon resorption as bone is remodeled.

47. Between adjoining lamellae are lacunae or spaces, with radiating canaliculi . inside a lacuna is present an osteocyte . In the radiating canaliculi lie cytoplasmic process of the osteocytes. They make gap junction ( connexins ) with processess of other osteocytes allowing for exchange of nutrients. Compact bone cont’

48. Compact bone cont ’ The structural and functional unit of compact bone is osteon/ haversian system. A central haversian canal contains blood vessels , nerve fibers and surronded by concentric lamellae. Compact bone. Stain: silver stain. Medium magnification

49. Histologic slide of compact bone

50. Compact bone ( section of long bone) Periosteum Haversian system/Osteon endosteum inner circumferential lamellae interstitial lamellae collagen fibers outer circumferential lamellae lacuna with osteocyte Haversian canal osteonal endosteum lamellae of bone Volkmann's canal Spongy bone

51. Compact bone The matrix in immature bone stains more intensely with hematoxylin, whereas the matrix of mature bone stains more intensely with eosin. GROUND SECTION PREPARATION H/E

52. Histogenesis of bone ( Osteogenesis ) Has 2 stages Formation of oteoid tissue ( organic matrix ) Mineralization of the osteoid tissue ( inorganic matrix )

53. Formation of bone tissue Osteoblasts form osteoid (the organic matrix) by secreting: Type I collagen, several glycoproteins, and proteoglycans such as osteocalcin that binds Ca 2+ together with various glycoproteins.   Matrix vesicles containing alkaline phosphatase and other enzymes that hydrolyze PO 4 ions from various macromolecules.

54. Mineralization of the bone tissue Crystals of CaPO 4 Are formed from the Ca 2+ and PO 4 ions on the matrix vesicles . Further grow and mineralize forming hydroxyapatite crystals [Ca 10 (PO 4 ) 6 (OH) 2 ] which surround the collagen fibers and all other macromolecules resulting in mineralized matrix .

55. Bone Development or Osteogenesis The development of a bone is traditionally classified as endochondral or intramembranous . The distinction between endochondral and intramembranous formation rests on whether a cartilage model serves as the precursor of the bone ( endochondral ossification) or whether the bone is formed by a simpler method, without the intervention o f a cartilage precursor ( intramembranous ossification).

56. Osteogenesis cont’ The bones of the extremities and those parts of the axial skeleton that bear weight (e.g., vertebrae ) develop by endochondral ossification . The flat bones of the skull , face , mandible , and clavicle develop by intramembranous ossification . The existence of two distinct types of ossification does not imply that existing bone is either membrane bone or endochondral bone. These names refer only to the mechanism by which a bone is initially formed .

57. Endochondral Ossification of Bone Ossify through a hyaline cartilage model . First bone collar is formed from the perichondrium by intramembranous ossification to prevent diffusion to the underlying avascular cartilage.

58. Endochondral ossification

59. Endochondral Ossification of Bone Lack of diffusion into the cartilage model, successively causes: Hypertrophy of the chondrocytes to compress the matrix into spicules and secrete type X collagen which limits diffusion . growth factors promotes vascularization as a primary ossification centre. 2. Apoptotic chondrocytes release matrix vesicles & osteocalcin for matrix calcification and formation of hydroxyapatite crystals .

60. Endochondral Ossification of Bone 3. Death of chondrocytes creates empty spaces with spicules of calcified cartilage matrix. 4. Osteoblasts arrive and line the spicules and form woven bone which will be remodeled as lamellar bone , forming diaphysis.

61. Endochondral Ossification of Bone Growth in the circumference of long bones occurs through appositional growth by: Osteoblasts develop from osteoprogenitor cells in the periosteum and forming bone collar. Enlargement of the marrow cavity by osteoclasts in the endosteum .

62. Endochondral Ossification of Bone Epiphyseal plate In between the primary and secondary centres of ossification. Shows five zones Gives metaphysis and articular cartilage .

63. Endochondrial ossification zones

64. Intramembranous ossification In utero before week 8 , all bone formed from hyaline cartilage and fibrous membranes . Intramembranous ossification give rise to cranial bones , clavicle and most flat bones . Formation Mesenchymal stem cells aggregate and form osteoblasts by differentiation. Then ossification center forms. osteblasts begin to secret osteoid (unmineralized bone)

65. Intramembranous ossification cont.. peripheral mesenchymal cells continue to differentiate. osteoblasts secrets osteoids inward toward ossification center . osteoblasts become trapped in osteoid, causing differentiation into osteocytes. osteoids calcified and hardens after several days. osteoids continue to be deposited , assembled in random manner around embryonic blood vessels .

66. Intramembranous ossification Finally woven/ trabecular forms. mesenchymal begins to differentiate into periosteum . Now compact bone replaces woven at outer edge(layered). But internal spongy bone remains . vascular tissue with trabecular space forms red marrow . osteoblasts remain on bone surface to remodel when needed.

67. Bone Remodeling involves bone resorption as well as bone formation . Occurs continuously throughout life with 5%-10% of the bone turnover annually in healthy adult humans. In compact bone , remodeling resorbs parts of old osteons and produces new ones . Osteoclast secrets lysosomal enzymes Collagenase digests collagen fibers ECM HCL dissolves hydroxyapetite (Ca2+, po4) Osteoblasts secrets osteoprotegerin = Bind to rankels and slow osteoclast activity = secret osteoid seam and fill lacunae =after mineralization occure osteocytes appear in lacunae.

68. Bone Remodeling Osteoclasts remove old bone and form small , tunnel-like cavities which will quickly be invaded by osteoprogenitor cells from the endosteum or periosteum and sprouting loops of capillaries . Osteoblasts develop , line the wall of the tunnels, and form a new osteon.

69. Bone Remodeling Show continuous exchange of calcium with blood and tissue by: A rapid transfer of calcium from hydroxyapatite crystals of mainly the young and lightly calcified lamellae of spongy bones. 2. A slower transfer of calcium under the regulation of: Parathyroid hormone - stimulate bone resorption. Calcitonin hormone from parafolicular cells of thyroid - inhibits bone resorption. 2.Vit –D stimulates calcium absorption from intestine thus it facilitates bone resorption.

70. Fracture Fracture is a break in the continuity of bone. Causes of fracture can be :- Trauma- a fall, motor vehicle accident or tackle during a football game can result in fracture. Osteoporosis-This disorder weakens bones and makes them more likely to break.

71. Bone remodeling and repair Bone remodeling is the replacement of old bone tissue by new bone tissue. Bone remodeling continues after birth into adulthood. It involves the process of bone deposition or bone production done by osteoclasts, which break down old bone.

72. A fractured bone undergoes repair through four stages Hematoma formation :- Blood vessels in the broken bone tear and hemorrhage, resulting the formation of clotted blood or a hematoma at the site of the break. The severed blood vessels at the broken ends of the bone are sealed by the clotting process. Bone cells deprived of nutrients begin to die.

73. 2 . Bone generation :- Within days of the fracture capillaries grow into the hematoma, while phagocytic cells begin to clear away the dead cells. Tough fragments of the blood clot will remain. Fibroblasts and osteoblasts enter the area and begin to reform bone. Fibroblasts produce collagen fibers that connect the broken bone ends.

74. Bone regeneration cont… While osteoblasts begin to form spongy bone. The repair tissue between the broken bone ends, the fibrocartlaginous callus is composed of both hyaline and fibrocartilage. Some bone spicules may also appear at this point.

75. 3 . Bony callous formation :- the fibrocartilaginous callus is converted in to a bony callus of spongy bone. It takes about two months for the broken bone ends to be firmly joined together after a fracture. This is similar to the endochondral bone formation when cartilage becomes ossified. Osteoblasts,osteoclasts and bone matrix are present .

76. 4 . Bone remodeling :- the bony callus is then remodelled by osteoclasts and osteoblasts with the excess material on the exterior of the bone and within the medullar cavity being removed. Compact bone is added to create bone tissue that is similar to the original unbroken bone This remodeling can take many months; the bone may remain uneven for years.

77. Joints Joints are the regions where adjacent bones are capped and held together firmly by other connective tissues . Functions of joints Facilitate bone growth Protecting vital organs Acts as shock absorber Facilitate all types of movement

78. Classification of joints Based on s tructure joints can be classified as:- Fibrous Cartilaginous Synovial Based on mobility Synarthroses No or limited movement Diarthroses Free movement

79. A) Synarthroses (Gr . syn , together + arthrosis , articulation). This joints allow very limited or no movement. Are subdivided based on the type of tissue joining the bones into F ibrous Synostoses Syndesmoses gomphosis Cartilaginous joints , synchondrosis , symphyses

80. 1.Synostoses Involve bones linked to other bones and allow essentially no movement . In older adults synostoses unite the skull bones, which in children and young adults are held together by sutures , or thin layers of dense connective tissue with osteogenic cells.

81. 2.Syndesmoses J oin bones by dense connective tissue only. Examples include the interosseous ligament of the inferior tibiofibular joint and the posterior region of the sacroiliac joints contains much more connective tissue than does a suture, allowing somewhat more movement .

82. 3.Gomphosis the, a peg-and-socket joint restricted to the fixation of teeth in the alveolar bone of the jaws. Periodontal ligament

83. Cartiliginous joints are present when bones are united by a continuous plate of hyaline cartilage or a disc of fibrocartilage. And can be S ynchondrosis Symphyses

84. Synchondrosis Are cartilaginous joints where bones are joined together by hyaline cartilage, or united by cartilage. It can be temporary or permanent Temporary – epiphyseal plate of long bone Permanent – first sternocostal joint.

85. Symphyses Cartilaganous joint where bones are joined by fibrocartilage. Fibrocartilage is very strong because it contains the numerous bundles of thick collagen fibers, thus giving it much greater ability to resist pulling and bending forces when compared with hyaline cartilage. Eg . Pubic symphysis M anubriosternal joint Intervertebral symphysis

86. Intervertebral discs A re large symphyses between the articular surfaces of successive bony vertebral bodies. Cushion the bones and facilitate limited movements of the vertebral column. Each disc has an outer portion, the annulus fibrosus , consisting of concentric fibrocartilage laminae in which collagen bundles are arranged orthogonally in adjacent layers In center it contains gel like body called the nucleus pulposus

87. Section of a rat tail showing an intervertebral disc and the two adjacent vertebrae with bone marrow (BM) cavities. The disc consists of concentric layers of fibrocartilage, comprising the annulus fibrosus (AF), which surrounds the nucleus pulposus (NP). The nucleus pulposus contains scattered residual cells of the embryonic notochord embedded in abundant gel-like matrix. The intervertebral discs function primarily as shock absorbers within the spinal column and allow greater mobility within the spinal column. (

88. Reference 1.Netters Essential Histology 2 nd edition 2.Junqueir as Histology 2013 3.Principles of Human anatomy G -Tortora 4.Ross Histology a text and an atlas 6 th edition

89. Thank you 4/7/2023 102