Bone Histology PDF - University of Northern Philippines

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC9 BONE HISTOLOGY COLLEGE OF MEDICINE, BATCH 2026 Transcribers/ Editors: Guzman...

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC9 BONE HISTOLOGY COLLEGE OF MEDICINE, BATCH 2026 Transcribers/ Editors: Guzman, A.L., Maligpas, X.E., Dr. Modesto David A. Bolislis | Nov. 14, 2022 Matanguihan, N., Nericua, N. BONE HISTOLOGY - Magnesium - Potassium I. FUNCTIONS - Sodium II. COMPONENTS - Non-crystalline calcium phosphate A. Bone Matrix The organic matter embedded in the calcified matrix is 90% B. Bone Cells type I collagen, but also includes mostly small III. COVERINGS OF THE BONE proteoglycans and multiadhesive glycoproteins such as A. Periosteum B. Endosteum osteonectin IV. TYPES OF BONES Calcium binding proteins (Osteocalcin) and phosphates A. According to Structure promote calcification of matrices. B. According to Shape Association of minerals with collagen fibers during C. According to the Pattern of Collagen calcification contributes to the hardness and resistance of V. OSTEOGENESIS the bone. A. Intramembranous B. Endochondral VI. BONE GROWTH B. BONE CELLS A. Longitudinal growth a. Osteocytes B. Growth in circumference (appositional growth) found in cavities (lacunae) between bone matrix layers VII. BONE REMODELING AND REPAIR (lamellae) with cytoplasmic processes into small VIII. METABOLIC ROLE OF THE BONE canaliculi IX. JOINTS A. Synarthroses B. Diarthroses I. FUNCTIONS Provides solid support for the body Protects vital organs such as those in the cranial and thoracic cavities Encloses internal (medullary) cavities containing bone marrow where blood cells are formed Reservoir of calcium, phosphate, and other ions The connections between the bones will form a system of levers that multiply the forces generated during skeletal muscle contraction and transform them into bodily movements (ex: flexion, extension, Figure 1. Osteocytes in lacunae abduction, adduction, etc.) b. Osteoblasts II. COMPONENTS growing cells that synthesize and secrete organic Bone is a specialized connective tissue composed of the following components of the matrix including type I collagen components: fibers, proteoglycans, and matricellular glycoproteins such as osteonectin. A. BONE MATRIX Deposit inorganic components in he bone Calcified extracellular material active osteoblasts at the surfaces of bone matrix are About 50% of the dry weight of bone matrix is inorganic bound by integrins, typically forming a single layer of materials. cuboidal cells joined by adherent and gap junctions - Calcium hydroxyapatite: most abundant during the processes of matrix synthesis and - Bicarbonate calcification, osteoblasts are polarized cells with - Citrate ultrastructural features denoting active protein synthesis and secretion 1 [HISTOLOGY] 1.09 BONE HISTOLOGY – Dr. Modesto David A. Bolislis matrix components secreted at the cell surface produce ○ binds the cell tightly to the bone matrix and a layer of unique collagen-rich material called osteoid surrounds an area with many surface the process of matrix mineralization is not completely projections, called the ruffled border understood, but basic aspects of the process are ○ allows formation of a specialized shown in the figure below: microenvironment between the osteoclast and the matrix where bone resorption occurs Figure 3. Osteoclast’s circumferential sealing zone Figure 2. Mineralization in bone matrix Osteoblasts will initially release your matrix vesicles → Formation of collagen fibers → Mineralization around the matrix vesicles → Mineralized bone Some osteoblasts become surrounded by the material they secrete and then differentiate as osteocytes are enclosed singly within the lacunae spaces throughout the mineralized matrix. c. OSTEOCLASTS Figure 4. Diagram showing the relationship of osteoblasts are very large, motile cells with multiple nuclei that are to the newly formed matrix called “osteoid”, bone matrix and essential for matrix resorption during bone growth and osteocytes bone tissue remodeling origin: fusion of bone marrow-derived monocytes III. COVERINGS OF THE BONE development requires 2 polypeptides produced by osteoblasts: External and internal surfaces of all bones are covered by ○ Macrophage colony stimulating factor (M-CSF) connective tissue. ○ Receptor activator of nuclear factor k-B ligand (RANKL) A. PERIOSTEUM - external surface Resorption Lacunae (Howship's lacunae) - same as perichondrium depressions or cavities in the matrix where the layers: osteoclasts lie during bone resorption ○ outer fibrous layer - dense connective tissue containing mostly bundled type 1 collagen Circular Sealing Zone ○ inner cellular layer - contains osteoblasts, bone lining ○ formed by the membrane domain that contacts cells, and osteoprogenitor cells (play a role in bone the bone in an active osteoclast growth and repair 2 [HISTOLOGY] 1.09 BONE HISTOLOGY – Dr. Modesto David A. Bolislis Perforating fibers (Sharpey fibers) - periosteal collagen that bone remodeling resorbs parts of old osteons and penetrates the bone matrix and bind the periosteum to the produces new ones, and it occurs continuously bone throughout life and resorbs parts of old osteons and produces new ones 2. CANCELLOUS (TRABECULAR) deeper areas with numerous interconnecting cavities 20% of total bone mass B. According to Shape 1. LONG BONE - arms and legs Epiphyses - bulbous ends of long bones ○ composed of cancellous bone covered by a thin layer of compact cortical bone Diaphysis - body of the long bone ○ almost totally dense compact bone with a thin Figure 5. Periosteum in a Compact Bone region of cancellous bone on the inner surface around the central marrow cavity B. ENDOSTEUM - internal surface very thin layer 2. SHORT BONE - wrist and ankle covers small trabeculae of bony matrix that projects into has cores of cancellous bone surrounded completely marrow cavities by compact bone also contains osteoprogenitor cells, osteoblasts, and bone lining cells, but within a sparse delicate matrix of collagen 3. FLAT BONE - calvaria (skullcap) fibers has 2 layers of compact bone called plates, separated by a thick layer of cancellous bone called diploe C. According to Pattern of Collagen Bones show 2 types of organization at microscopic level: 1. LAMELLAR BONE mature - most bones in adults, compact or cancellous, is organized as lamellar bone with matrix - multiple layers or lamellae of calcified matrix existing as discrete sheets - organized as parallel Figure 6. Endosteum in a Cancellous bone sheets or concentrically around a central canal In each lamella, type I collagen fibers are aligned, with IV. TYPES OF BONES the pitch of the fibers’ orientation shifted orthogonally (by about 90 degrees) in successive lamellae A. According to Structure alternating orientation of the collagen fibers (first layer going to the right, then the next is going the left) contributes greatly to the strength of lamellar bone 1. COMPACT (CORTICAL) dense area near the surface(immediately beneath the OSTEON (HAVERSIAN SYSTEM) periosteum) - functional unit of the bone 80% of the total bone mass - complex of concentric lamellae, surrounding a central includes parallel lamellae organized as multiple canal that contains small blood vessels, nerves, and external circumferential lamellae immediately beneath endosteum the periosteum and fewer inner circumferential lamellae around the marrow cavity 3 [HISTOLOGY] 1.09 BONE HISTOLOGY – Dr. Modesto David A. Bolislis - each functional unit is a long, sometimes bifurcated, cylinder generally parallel to the long axis of the diaphysis - 5-20 concentric lamellae around the central canal that communicates with the marrow cavity and periosteum - canals communicate with one another through transverse perforating canals (or Volkmann canals) - scattered among the intact osteons are numerous irregularly shaped groups of parallel lamellae called interstitial lamellae. Contributing to the formation of the interstitial lamellae are the following generations of osteons with different degrees of mineralization First Generation Osteons - least mineralized Second Generation Osteons Third Generation Osteons - most mineralized Figure 9. Successive generations of osteons - Figure 10. Development of Osteon Figure 7. Osteon (Haversian System). Shown here are the lamellae (L), central canal (CC), osteocytes 2. WOVEN BONE (O), canaliculi (C) and the interstitial membrane (I) newly formed with randomly arranged components (immature bone) non lamellar and characterized by random disposition of type I collagen fibers in a calcified matrix first bone tissue to appear in embryonic development and in fracture repair usually temporary and is replaced in adults by lamellar bone except in the sutures of the calvaria and tendon insertions has low mineral content that’s why it is more easily penetrated by x-rays has higher proportion of osteocytes than lamellar bone forms more quickly but has less strength than lamellar bone Figure 8. Volkmann Canals (P) 4 [HISTOLOGY] 1.09 BONE HISTOLOGY – Dr. Modesto David A. Bolislis pre-existing matrix of hyaline cartilage is eroded and invaded by osteoblasts, which then begin osteoid production all other bones; especially well studied in developing long bones Figure 11. Summary of bone types and their organization V. OSTEOGENESIS OSTEOGENESIS - bone development or bone formation that occurs by one of the two processes: A. INTRAMEMBRANOUS OSSIFICATION osteoprogenitor cells arise, proliferate, and form incomplete layers of osteoblasts around a network of developing capillaries osteoblasts differentiate within the condensed sheets (membranes) of embryonic mesenchymal tissue and begin secreting osteoid, which calcifies and forms the small irregular areas of woven bone with osteocytes in Figure 13. Osteogenesis of long bones by endochondral lacunae and canaliculi ossification. the following bones begin to form embryonically by intramembranous ossification: In both processes, woven bone is produced first and is ○ most flat bones soon replaced by stronger lamellar bone. ○ most bones of the skull and jaws ○ scapula In the process of endochondral ossification, two ○ clavicle ossification centers are formed: in cranial flat bones, lamellar bone formation predominates over bone resorption at both the internal and external 1. PRIMARY OSSIFICATION CENTER surfaces - diaphyses of fetal long bones ○ internal and external plates of compact bone arise - form when chondrocytes die after enclosure of the ○ central portion (diploe) maintains its cancellous cartilage within a collar of woven bone, creating an nature initial cavity that is entered by periosteal Example: fontanelles on the heads of newborn infants osteoblasts and vasculature where membranous tissue not yet ossified 2. SECONDARY OSSIFICATION CENTER - develop similarly within the epiphyses, with cartilage of the epiphyseal growth plate between the primary and secondary ossification sites With the primary and secondary ossification centers, two regions of cartilage remain: 1. ARTICULAR CARTILAGE - within the joints between long bones - persists through adult life Figure 12. Intramembranous ossification 2. EPIPHYSEAL CARTILAGE/EPIPHYSEAL PLATE/GROWTH PLATE B. ENDOCHONDRAL OSSIFICATION - connects each epiphysis to the diaphysis takes place within hyaline cartilage shaped as a small - longitudinal bone growth version or model of the bone to be formed 5 [HISTOLOGY] 1.09 BONE HISTOLOGY – Dr. Modesto David A. Bolislis - disappears upon completion of bone development B. APPOSITIONAL GROWTH at adulthood growth in the circumference of long bones does not involve - epiphyseal closure occurs at various times with endochondral ossification but occurs through the activity of different bones osteoblasts developing from osteoprogenitor cells in the - about age 20, bone growth is complete periosteum and further growth in bone length is no accompanied by enlargement of the medullary marrow longer possible (height during 20’s will be cavity most probably your height through begins with formation of the bone collar on the cartilaginous adulthood) diaphysis Epiphyseal growth plate shows distinct regions of cellular activity and often discussed in terms of overlapping but histologically distinct zones (distal to proximal zone): 1. Resting or reserve zone - composed of hyaline cartilage 2. Proliferative zone - cartilage cells divide repeatedly, enlarge and secrete type II collagen and proteoglycans 3. Hypertrophic zone - swollen terminally differentiated Figure 15. Appositional Bone Growth chondrocytes which compress matrix by type X collagen secretion VII. BONE REMODELING AND REPAIR 4. Zone of calcified cartilage - chondrocytes undergo apoptosis (program cell death) and the matrix Bone growth involves both the continuous resorption of bone tissue calcification begins by hydroxyapatite formation formed earlier and the simultaneous laying down of new bone at a rate exceeding that of bone removal. 5. Zone of ossification - bone tissue first appears; bones change size and shape according to changes in capillaries and osteoprogenitor cells invade the vacant mechanical stress chondrocytic lacunae going to bone marrow cavity bone turnover is very active in young children (200 times faster than adults) adult skeleton is also renewed continuously (bone remodeling that involves the coordinated, localized cellular activities for bone resorption and bone formation) constant bone remodeling ensures: ○ tissue remains plastic despite its hardness ○ capable of adapting its internal structure in the face of changing stresses Bone repair after a fracture or other damage uses cells, signaling molecules, and processes already active in bone remodeling. Major phases that occur during bone fracture: ○ Initial formation of fibrocartilage - activation of Figure 14. Epiphyseal growth plate: Locations and zones of activity. periosteal fibroblasts to produce an initial soft callus of fibrocartilage-like tissue Diseases that affects some of the zones of locality ○ Replacement with a temporary callus of woven - gigantism bone - soft callus is gradually replaced by a hard - acromegaly callus of woven bone and is remodeled to produce stronger lamellar bone VI. BONE GROWTH A. LONGITUDINAL GROWTH OF BONE occurs by cell proliferation in the epiphyseal plate cartilage 6 [HISTOLOGY] 1.09 BONE HISTOLOGY – Dr. Modesto David A. Bolislis children and young adults: sutures b. Syndesmoses join bones by dense connective tissue only interosseous ligament of the inferior tibiofibular joint; posterior region of sacroiliac joints c. Symphyses Figure 16. Main feature of bone fracture repair thick pad of fibrocartilage between the thin articular cartilage covering the ends of the bones. VIII. METABOLIC ROLE OF THE BONE Symphysis pubis; IV (intervertebral) disk Intervertebral discs are large symphyses between the Calcium ions are required for the activity of many enzymes and articular surfaces of successive bony vertebral bodies. many proteins mediating cell adhesion, cytoskeletal Each disc has: movements, exocytosis, membrane permeability, and other cellular function. 1. Annulus fibrosus The skeleton serves as the calcium reservoir containing 99% of - outer portion total body calcium in the form of hydroxyapatite crystals - consists of concentric fibrocartilage laminae in The principal mechanism for raising blood calcium levels is the which collagen bundles are arranged orthogonally mobilization of ions from hydroxyapatite to interstitial fluid, in adjacent layers. primarily in cancellous bone 2. Nucleus pulposus Two polypeptide hormones target bone cells to influence - inner portion; gel-like body calcium homeostasis: - consists of a viscous fluid matrix rich in hyaluronan a. Parathyroid hormone and type II collagen fibers - raises low blood calcium levels - scattered, vacuolated cells derived from the - stimulates osteoclasts and osteocytes to resorb embryonic notochord bone matrix and release calcium - shock absorber - it absorbs forces that are being - PTH (parathyroid hormone) receptors occur on acted upon by the superior portion of your spinal osteoblasts, which respond by secreting RANKL column and other paracrine factors - large in children, but gradually become smaller with b. Calcitonin age and are partially replaced by fibrocartilage - produced in the thyroid gland - reduces elevated calcium levels - counteracts PTH - directly targets osteoclasts to slow matrix resorption and bone turnover IX. JOINTS Joints are regions where adjacent bones are capped and held together firmly by other connective tissues. The type of joint determines the degree of movement between bones. A. SYNARTHROSES - allow very limited or no movement - subdivided into fibrous and cartilaginous joints Figure 17. Intervertebral Disc. Shown here are Annulus Fibrosus a. Synostoses (AF), Nucleus Pulposus (NP). bones linked to other bones no movement adults: skull bones 7 [HISTOLOGY] 1.09 BONE HISTOLOGY – Dr. Modesto David A. Bolislis B. DIARTHROSES - permit free bone movement - examples of which are metacarpophalangeal joint or knuckle, knees and elbows Figure 18. Diarthroses or Synovial Joints Figure 19. Articular cartilage of Diarthroses - in different diarthrotic joints, the synovial membrane may have prominent regions with dense connective tissue or fat. This area is characterized by two specialized cells with distinctly different functions and origins: REFERENCES a. Macrophage synovial like cells Mescher, A. L. (2016). Junqueira’s Basic Histology Text and Atlas Type A cells (Fourteenth Edition). McGraw-Hill Education derived from blood monocytes remove wear-and-tear debris from the synovial Powerpoint Presentation of Dr. M. Bolislis. S.Y. 2023-2023.Bone fluid Histology. University of Northern Philippines - College of Medicine important in regulating inflammatory events within diarthrotic joints b. Fibroblastic synovial cells Type B cells produce abundant hyaluronan and smaller amounts of proteoglycans. form the synovial fluid which: - lubricates the joint - reducing friction on all internal surfaces - supplies nutrients and oxygen to the articular cartilage. - The collagen fibers of the hyaline articular cartilage are disposed as arches with their tops near the exposed surface which, unlike most hyaline cartilage, is not covered by perichondrium. 8