Bone and Cartilage Anatomy Lecture Notes PDF

ANATOMY-LEC: LE 2 | TRANS 1 CARTILAGE AND BONE MA. CARMERIZA B. BUNING, MD, FPOGS | 09/13/2024 OUTLINE B. FUNCTIONS I. Cartilage...

ANATOMY-LEC: LE 2 | TRANS 1 CARTILAGE AND BONE MA. CARMERIZA B. BUNING, MD, FPOGS | 09/13/2024 OUTLINE B. FUNCTIONS I. Cartilage A. Histologic/Microscopi Allows tissues to bear mechanical stress 📖 A. Definition c → Cartilage ECM’s firm consistency allows it to bear B. Functions B. Gross/Macroscopic mechanical stress without permanent distortion C. Components VIII. Bone Architecture → Ex. Cartilage in the Intervertebral discs D. Characteristics A. Long Bones Facilitates bone movements II. Types of Cartilage B. Lamellar Bones → Shock absorbing and sliding regions within joints A. Hyaline Cartilage IX. Histologic Preparations B. Elastic Cartilage A. Ground Bone ▪ Synovial joints 📖 C. Fibrocartilage B. Decalcified Bone ▪ Molecular basis for shock absorbing properties: 📣 III. Cartilage Formation, X. Bone Formation Hydration of GAGs Growth, & Repair A. Intramembranous → Cartilage has a smooth surface ( well-lubricated) , A. Chondrogenesis Ossification 📣 specifically in the articulating surface of bones, B. Cartilage Growth B. Endochondral permitting almost friction free ( gliding) movements C. Cartilage Ossification of the joints. Regeneration & XI. Epiphyseal Plate Repair A. Definition Forms the framework supporting soft tissues IV. Bone B. Epiphyseal Growth → Ear, nose, walls of the respiratory tract A. Definition & Plate Guides development and growth of long bones Components XII. Clinical Applications → Endochondral ossification B. Functions A. Osteoporosis V. Bone surfaces XIII. Bone Growth, C. COMPONENTS A. Periosteum Remodeling, and Repair Cartilage is a CT composed of cells and predominantly of B. Endosteum A. Bone Growth ECM VI. Bone Cells B. Bone Remodeling A. Osteoblasts C. Bone Repair B. Osteocytes XIV. Review Questions C. Osteoclasts XV. References VII. Bone Classification XVI. Appendix SUMMARY OF ABBREVIATIONS CT Connective Tissue ECM Extracellular matrix GAGs Glycosaminoglycans RER Rough Endoplasmic reticulum Figure 1. Hyaline cartilage. C - chondrocytes, P - perichondrium, ❗️ 📣 📖 📋 Must know Lecturer Book Previous Trans M - matrix[Mescher, 2018] EXTRACELLULAR MATRIX (ECM) LEARNING OBJECTIVES Composed of: At the end of the lecture, the students should be able to → Ground Substance characterize the histology of CARTILAGE and BONE by: ▪ High concentration of GAGs (shock absorber) and ✔ Describing component parts densely packed proteoglycans responsible for semi ✔ Differentiating the 3 types of CARTILAGE as to composition of the intercellular substance, histologic ▪ 📣 rigid consistency GAGs are hydrophilic, has high amount of water, the reason why there is a shock absorbing ability in features and functions the cartilage tissue ✔ Classifying BONE according to morphology → Fibers “CartilagE” ✔ Explaining the process of formation, growth and repair ▪ Collagen & Elastic and regenerative capacity SUBDIVISIONS OF ECM I. CARTILAGE Territorial Matrix → Immediately surrounds chondrocytes A. DEFINITION → Stains more intensely with hematoxylin dye (due to Tough, durable form of supporting connective tissue, higher proteoglycan content) characterized by presence of cells embedded in an Interterritorial Matrix extracellular matrix (ECM) with high concentrations of → Lighter staining (lower proteoglycan content) Glycosaminoglycans (GAGs) and proteoglycans, → Between isogenous groups (from the word “inter”) 📖 interacting with collagen and elastic fibers → Differs from other CT because of its avascularity LE 2 TRANS 1 TG-A1: D. Riñosa, J. Rivera,, L. Roda, M. Rodriguez, M.., TE: L. Rioflorido, A. AVPAA: A. Roluna Page 1 of 14 Rodrigueza, M. Roldan Rivadavia  CELLS → Inner chondrogenic layer ▪ Blends with the matrix proper ▪ Contains chondroblasts and mesenchymal stem cells ▪ Function: Chondroblast synthesis Figure 2. Hyaline cartilage.[Mescher, 2018] 1. Chondroblasts Immature cartilage forming cells Elliptical in shape Found in the periphery (inner chondrogenic layer) 📣❗️ Undergo mitosis Figure 4. Components of Hyaline cartilage.[Lecturer’s PPT] Primary role: to secrete ECM to become II. TYPES OF CARTILAGE ❗️ chondrocytes No lacuna 3 types depending on the content of its matrix, and predominant fibers: 2. Chondrocytes → Hyaline: non rigid support ❗️ Round, mature cells surrounded by ECM → Elastic: support with high flexibility Lie within lacunae → Fibrocartilage: strength under stress May occur singly or in clusters (isogenous groups or aggregates) ○ Cells in an isogenous groups are daughter cells from a mitotic event ○ As the chondrocytes continue secreting ECM, 📣❗️ they are pushed away from each other Primary role: to maintain ECM (also secretes) Figure 5. Distribution of Cartilage in Adults.[Lecturer’s PPT] Figure 3. Chondrocytes in isogenous groups.[Lecturer’s PPT] 📣 for easier understanding: MNEMONIC ChondroBlasts = Baby A. HYALINE CARTILAGE Most common type of cartilage Forms the temporary skeleton which is gradually replaced ChondroCytes = Child (baby grew up to child) by bone D. CHARACTERISTICS ECM: Type II collagen Avascular (no blood vessels) Aggrecan most abundant proteoglycan ○ Low metabolic activity Chondronectin - Multiadhesive glycoprotein responsible ❗️ No lymphatic vessels and nerves for adherence of chondrocytes to the ECM Nutrition: Homogenous and semi transparent in fresh state ○ Via diffusion from vascularized outer covering “glass-like” appearance perichondrium → Refractive index of the Type II collagen fibers and 📣 ○ Exception: Articular surfaces of joints & Epiphyseal ground substance are nearly the same plates → Collagen fibers blends well with the matrix proper causing glass-like appearance PERICHONDRIUM → Under the microscope: Comes from greek word peri meaning “around” and chondros meaning “cartilage” ▪ Basophilic/stains blue because of proteoglycans Structure that forms an interface between the cartilage and ▪ Chondrocytes appear in groups (isogenous 📋 📋 tissue being supported aggregate/s) Arise from superficial embryonic mesenchyme EXAMPLES Essential for growth and maintenance of the cartilage Connective tissue surrounding cartilage Fetal skeleton → Outer fibrous layer Walls of large respiratory passages (nose, larynx, ▪ Dense irregular CT (Type I collagen fibers), trachea, bronchi) fibroblasts and blood vessels Ventral ends of ribs ▪ Functions: Collagen synthesis, nutrition ANATOMY Page 2 of 14  Epiphyseal plates* Elastic doesn't show a glass-like appearance and 📣❗️ Articular surfaces of movable joints* actually looks dirty due to uneven distribution of elastic All hyaline cartilage have perichondrium except fibers. articular surface of joints and epiphyseal plates → Clinical significance: Damage to these areas would mean that there will be a poor regenerative capability and poor healing Figure 8. Elastic-Hyaline comparison.[Lecturer’s PPT] —-------------------------------------------------------------------------------------------------------------------------------------- Tip: Think of taho (silken tofu) Arnibal / syrup - can be compared to elastic fibers that are unevenly distributed within the matrix of the elastic cartilage Figure 6. Hyaline cartilage.[Lecturer’s PPT] B. ELASTIC CARTILAGE Similar to hyaline cartilage → Also made up of Type II collagen fibers Surrounded by perichondrium Figure 9. Taho as Elastic cartilage.[Lecturer’s PPT] ❗️ Abundant elastic fibers Dark bundles unevenly distributed - “looks dirty” C. FIBROCARTILAGE Fewer isogenous groups than hyaline cartilage In between hyaline cartilage and dense CT Fresh elastic cartilage has yellowish color due to Abundant Type I collagen than Type II, arranged either in regular or irregular configuration 📋 containing an abundant network of elastic fibers in addition → helps in withstanding tensile forces 📣 to collagen Type II → reason why one of the functions of cartilage is to bear Elastic cartilage has “flexibility” mechanical stresses Less proteoglycan (stains pink) - appears acidophilic Minimal ground substance Few isogenous groups, axial fashion aggregates ( 📣 → If present, isogenous groups can be seen as aligned arranged like baguio beans) Great tensile strength cushioning, resistance to tearing and ❗️ compression No perichondrium → Nutrition comes via diffusion from blood vessels or from synovial fluids Figure 7. Elastic cartilage. C - chondrocytes, M - matrix, EXAMPLES P - perichondrium.[Mescher, 2018] → Intervertebral discs → Attachments of certain ligaments EXAMPLES → Pubic symphysis Located in areas where both flexibility & support are necessary: →Pinna of Ears →External auditory canal →Epiglottis →Cuneiform cartilage of the larynx 📋 📋 → Auditory or eustachian tube → Upper respiratory tract REVIEW: Elastic and Hyaline Comparison Figure 10. Section of pubic symphysis. C - chondrocytes, M - matrix, Hyaline cartilage appears homogeneous and has a D - dense regions with more Type I collagen[Mescher, 2018] glass-like appearance More isogenous are appreciated in Hyaline than in Elastic cartilage Both have perichondrium (both have nutritional support) Elastic has few isogenous aggregates and less homogenous ANATOMY Page 3 of 14  Figure 13. Cartilage Growth[Lecturer’s PPT] Figure 11. Region of intervertebral disc. C - chondrocytes, M - matrix, D - dense collagen, and fibroblasts with elongated nuclei C. CARTILAGE REGENERATION & REPAIR (pointed by the arrows)[Mescher, 2018] Slow, ineffective and often incomplete (in adults) Generally poor due to avascularity III. CARTILAGE FORMATION, GROWTH AND REPAIR → Poor access to necessary nutrients A. CHONDROGENESIS Optimum nutrition depends on (+/-) perichondrium Chondrogenesis: Formation of cartilage (comes from → If there is no perichondrium, regeneration and repair will mesenchyme) result in a much slower and poorer capability of regeneration Clinical Correlations involving the Cartilage: Arthritis Figure 12. Chondrogenesis [Mescher, 2018] Figure 14. Osteoarthritis of the knee (left) & Rheumatoid As seen in Figure 12, the following are the major stages by arthritis (right) which embryonic cartilage is formed: → AKA wear and tear arthritis because it develops as a. Rounding up of mesenchymal cells the cartilage in the joints wear down ▪ During chondrogenesis, there will first be → As the cartilage in the joints are being damaged, this rounding up of mesenchymal cells and allows the bone to rub against each other, resulting condensation ▪ 📣 perichondrium came from superficial in joint stiffness, pain and swelling → The knees are markedly swollen, same as in the knuckles of the hands mesenchymal cells b. Mitosis, chondroblasts → Usually common in the elderly but may be seen in ▪ Undergoes mitosis and differentiation into younger populations as well chondroblasts ▪ Chondroblasts secrete matrix among themselves IV. BONE c. Separated from one another and would reside in A. DEFINITION & COMPONENTS the lacunae Bone is a specialized type of CT characterized by its ▪ Chondroblasts then become trapped within a rigidity and hardness lacuna and become separate from one another, Made up of the following components: becoming chondrocytes → Matrix: Inorganic and Organic d. Continuous multiplication within lacunae → Cells: Osteoblasts, Osteocytes, and Osteoclasts ▪ Continuous matrix secretion and mitosis eventually result in formation of new cartilage MATRIX B. CARTILAGE GROWTH ORGANIC PORTION 📣 Interstitial growth Mainly Type I collagen fibers → Mitotic division of ( withIN) pre-existing chondrocytes Stain pink with eosin → Seen in articular cartilage and epiphyseal plates Minimal ground substance Appositional growth Proteoglycans, Glycoproteins, Osteonectin, Osteocalcin, → Differentiation of new chondroblasts from progenitor Phosphatases → 📣 cells perichondrium APO = lolo/lola = ancestors, means it came from →Important for binding collagen, calcium, calcification INORGANIC PORTION progenitor cells 50% of dry weight of bone matrix → More important in postnatal development Calcium hydroxyapatite (most abundant) Calcium phosphate (significant amount) Other ions: HCO3-, Citrate, Mg 2+, K+, Na+ ANATOMY Page 4 of 14  B. FUNCTIONS VI. BONE CELLS Provides structural support and protection A. OSTEOBLASTS → Giving shape & form to the body Derived from mesenchymal stem cells Permit movement (provides insertion of muscles) Exclusively at the surface of the bone matrix Serves as a storage for minerals such as calcium Single layer of Cuboidal cells Houses bone marrow (for blood cell formation) → Inactive form (bone lining cells): Flattened with → Myeloid tissue = bone cell precursors heterochromatic nuclei V. BONE SURFACES → Active form: cuboidal or columnar in shape with basophilic cytoplasm A. PERIOSTEUM Functions: Double layer of CT surrounding outer bone surface → Secrete organic bone matrix (OSTEOID) Similar to perichondrium → Type I collagen, glycoprotein → Well vascularized → Synthesize osteocalcin and alkaline phosphatase in → Absent at articular surfaces membrane- enclosed matrix vesicles LAYERS OF PERIOSTEUM ▪ Formation of hydroxyapatite crystals Outer fibrous → Dense CT most Type I collagen ▪ Mineralization of osteoid → Small blood vessels, collagen bundles, fibroblasts Inner osteogenic → Osteoprogenitor cells → Osteoblasts → Osteoclasts → Bone lining cells (inactive osteoblasts) Perforating/Sharpey fibers → Bundles of periosteal collagen fibers that act like a glue to bind periosteum to the bone Figure 17. Relationship of osteoblasts to osteoid, bone matrix, and osteocytes [Mescher, 2018] [Mescher, 2018] Figure 15. Periosteum & perforating fibers B. ENDOSTEUM Figure 18. Photomicrograph of developing bone. Ob - osteoblasts, Internal surface of bones/trabeculae Oc - osteocytes, Os - osteoid, M - mesenchyme, B - bony Single row of bone lining cells, osteoblasts, osteoclasts & matrix[Mescher, 2018] 📖 osteoprogenitor cells Calcification of the matrix is not completely understood , but basic aspects of the process are shown in Figure 19. Figure 16. Endosteum covering trabeculae around the marrow cavities [Mescher, 2018] Figure 19. Mineralization in bone matrix[Mescher, 2018] ANATOMY Page 5 of 14  B. OSTEOCYTES Differentiated osteoblasts surrounded by matrix enclosed singly within lacunae Almond-shaped cells containing long dendritic processes → Communicate with one another via long cytoplasmic processes that contain gap junctions → Long processes also aids in transport of nutrient Lined with dendritic processes within canaliculi Functions: → Maintain the bone matrix → Role in transport of nutrients between blood & bone, calcium homeostasis → Detection of mechanical stresses to direct bone Figure 22. Osteoclasts[Lecturer’s PPT] remodeling ▪ Mechanostat: network of dendritic processes extending from osteocytes − Monitors areas where loading has increased or decreased − Signals cells to adjust ion levels and maintain adjacent matrix ▪ Bone density can be increased with mechanical 📣 stimulation of bone cells Extensive dendritic process allows bone remodeling Figure 23. Schematic of osteoclast[Mescher, 2018] Osteoclasts circumferential sealing zone → Integrins tightly bind the cell to the bone matrix. → The sealing zone surrounds a ruffled border of microvilli and other cytoplasmic projections close to this matrix. ▪ The sealed space between the cell and the matrix is acidified to ~pH 4.5 by proton pumps in the ruffled part of the cell membrane and Figure 20. TEM of an osteocyte in a lacuna with canaliculi (C) [Mescher, receives secreted matrix metalloproteases and 2018] other hydrolytic enzymes. → Acidification of the sealed space promotes dissolution of hydroxyapatite from bone and stimulates activity of the protein hydrolases, producing localized matrix resorption. ▪ The breakdown products of collagen fibers and other polypeptides are endocytosed by the osteoclast and further degraded in lysosomes, while Ca2+ and other ions are released directly and taken up by the blood. Figure 21. Photomicrograph of bone showing the darkly stained lacunae and canaliculi (C) [Mescher, 2018] C. OSTEOCLASTS Derived: monocyte-macrophage cell line Large, motile, multinucleated, vacuolated cells with, frothy cytoplasm Lie in depression in bone surfaces (resorption bay/ cavity/ Howship Lacunae) Ruffled border: part of cell membrane facing the site of bone resorption Figure 24. Photomicrograph of osteoclasts[Lecturer’s PPT] Functions: → Bone resorption VII. BONE CLASSIFICATION ▪ Secrete lysosomal enzymes to dissolve A. HISTOLOGIC/ MICROSCOPIC CLASSIFICATION hydroxyapatite and digest matrix proteins that will lead to bone resorption WOVEN OR IMMATURE OR PRIMARY BONE → Osteoclast activity is inhibited by calcitonin (thyroid 📣 gland) and activated by parathyroid hormone Think of spongebob 📣 First bone deposited Only immature bone →MNEMONICS: WHIP NAE NAE = nene = immature ANATOMY Page 6 of 14  Osteocytes and collagen fibers randomly arranged Less mineralized than lamellar bone Examples: → Bone tissue in embryonic development → Bone tissue in fracture repair LAMELLAR OR MATURE OR SECONDARY BONE Replaces most woven bone Deposited in layers or lamellae Better mineralized than woven bone B. MACROSCOPIC / GROSS CLASSIFICATION: MATURE COMPACT OR CORTICAL BONE Solid portion covering the exterior of bones and forming the shaft of the long bones 80% of total bone mass Lined by periosteum CANCELLOUS (SPONGY / TRABECULAR / MEDULLARY) Figure 26. Structure of a typical long bone[Ross & Pawlina, 2011] Interior of bone Covered by endosteum B. ARCHITECTURE OF LAMELLAR BONES 📣 Labyrinth of bony spicules or trabeculae Osteon or haversian system → Trabeculae serve as a supporting structure that → Concentric lamellae (4 to 20) provides considerable strength without increasing the → Arranged around a central or haversian canal containing bone’s weight 📣 blood vessels and nerves Intervening spaces filled with loose CT or marrow → Looks like a tree trunk or cinnamon roll 20% of total bone mass Figure 25. Spongy bone[Lecturer’s PPT] VIII. BONE ARCHITECTURE A. ARCHITECTURE OF LONG BONES Epiphysis → Knob-like structure at both ends → Spongy bone covered by a thin rim of compact bone Diaphysis → Shaft of the long bone → Mostly composed of compact bone → Hollow center lines with thin region of spongy bone that Figure 27. Osteon diagram[Mescher, 2018] contains the marrow Cement line Metaphysis → Outer boundary of each osteon → Flared region between diaphysis and epiphysis Perforating / Volkmann canal Epiphyseal plate → Transverse canal that allows each osteon to ❗️ → Hyaline cartilage that separates the epiphysis and communicate with each other metaphysis → Differentiate perforating (transverse) canal to central → Region of endochondral bone formation (it is needed for (vertical) canal Lacunae bone elongation) → Spaces located between successive lamellae → Interconnected by canaliculi → Contain single osteocyte ANATOMY Page 7 of 14  Figure 31. Osteocytes lodged within a lacuna[Lecturer’s PPT] Figure 28. Lacunae[Mescher, 2018] Canaliculi Figure 32. Tree trunk and cinnamon danish similar to an osteon → Narrow tunnels between lamellae containing long (with central canal and concentric lamellae)[Lecturer’s PPT] dendritic processes of osteocytes External (outer) circumferential lamellae IX. HISTOLOGIC PREPARATIONS → Not associated and scattered along osteons A. GROUND BONE → Located immediately beneath the periosteum Unpreserved bone Internal (inner) circumferential lamellae → No chemicals or solutions were introduced to the bone → Located around the marrow cavity → Ground to thinness where light can be transmitted Interstitial lamellae → No visible preserved cells or organic matrix → Found in between osteons Lamellae, lacunae, canaliculi, and general organization of 📣 → Remnants of partially destroyed osteons during bone inorganic matrix are well displayed growth and remodeling Lacuna seen as black dots in Figure 33. Figure 33. Photomicrograph of ground bone [Lecturer’s PPT] 📣 B. DECALCIFIED BONE Cells ( black dots in Figure 34) fixed and inorganic matrix removed by decalcification Figure 29. Osteon. CC - central canal, L - concentric lamellae, Good detail of organic matrix cells and periosteum O - osteocyte, I - interstitial lamellae[Mescher, 2018] Lamellae and inorganic matrix difficult to distinguish Perforating canals are also visible Figure 30. Multiple Osteons with the Volkmann canal[Lecturer’s PPT] Figure 34. Photomicrograph of decalcified bone [Lecturer’s PPT] ANATOMY Page 8 of 14  Figure 38. Trabecular bone with blood vessels [Lecturer’s PPT] Figure 35. Two types of preparations showing the ground bone 3. Continuous deposition of bony matrix will eventually (top) and decalcified bone (bottom) [Lecturer’s PPT] form the bony spicules or trabecular bone a. Trabeculae is inundated with blood vessels X. BONE FORMATION i. Formation of the periosteum on the surface of In both processes (Intramembranous and Endochondral the bone. Ossification), woven bone is formed first then soon replaced by stronger lamellar bone. A. INTRAMEMBRANOUS OSSIFICATION Intramembranous ossification →Osteoblasts differentiate directly from mesenchyme Examples: →Flat bones of skill Figure 39. Compact bone and spongy bone [Lecturer’s PPT] →Fontanelles →Mandible and maxilla 4. Further deposition of the bony matrix would result in →Clavicle the trabeculae becoming the primary bone which is then replaced by a more stronger compact bone. a. Blood vessels that invaded the trabeculae would condense and become the red marrow. B. ENDOCHONDRAL OSSIFICATION Endochondral Ossification →Preexisting hyaline cartilage used as template Examples: →Bones of limbs Figure 36. Mesenchymal cells with ossification center [Lecturer’s PPT] →Pelvis 1. Bone formation via intramembranous ossification starts →Vertebral column with the mesenchymal cells cluster or condensation of mesenchymal cells with simultaneous formation of ossification centers. Figure 40. Mesenchymal cells with ossification center [Lecturer’s PPT] Figure 37. Formation of osteoblasts and osteocytes [Lecturer’s PPT] 1. Bone forms from a hyaline cartilage model 2. Mesenchymal cells will then differentiate into 2. Hyaline cartilage then undergoes degeneration osteoblasts. followed by the formation of a periosteal bone collar a. Osteoblasts then secrete bony matrix around around the diaphysis. themselves. a. Bone collar formation impedes diffusion of oxygen b. The osteoblasts would then be trapped within a and nutrients resulting in further cartilage lacunae, becoming osteocytes. degeneration and death of chondrocytes. i. Osteocytes deposit calcium and other mineral 3. Primary ossification center is formed in the diaphysis salts that harden the forming bone matrix. a. Penetrated by blood capillaries which brings in the osteoprogenitor cells ANATOMY Page 9 of 14  b. Osteoprogenitor cells secrete bone matrix or osteoid resulting in the formation of the woven bone. c. Woven bone in the primary ossification center will be replaced by a developing compact bone enclosing a medullary cavity 4. At the time of birth, secondary ossification center forms in epiphysis b. Figure 43. Resting zone of the Epiphyseal Plate [Lecturer’s PPT] PROLIFERATIVE ZONE Zone of Proliferating Cartilage Zone where the isogenous groups of chondrocytes actively divide and form columns of stacked cells parallel to the long axis of the bone Figure 41. Formation of osteoblasts and osteocytes [Lecturer’s PPT] 5. During childhood, primary and secondary ossification centers are separated by an epiphyseal plate or growth plate. a. Growth plate is responsible for bone elongation 6. Epiphyseal plates ossify and epiphyseal lines are formed a. Ossification centers fuse when the full stature of the person is achieved. (Around 20 yrs old for males and earlier for females) XI. EPIPHYSEAL PLATE Figure 44. Proliferative zone of the Epiphyseal Plate [Lecturer’s PPT] A. DEFINITION HYPERTROPHIC CARTILAGE ZONE Responsible for bone elongation Zone of Maturation and Hypertrophy Made up of five overlapping zones In this zone, the chondrocytes are swollen and there is → The typical order is from diaphysis to epiphysis an accumulation of glycogen in the cytoplasm Figure 42. Histologic view of the Epiphyseal Plate [Lecturer’s PPT] Figure 45. Hypertrophic Cartilage Zone of the Epiphyseal Plate [Lecturer’s PPT] B. EPIPHYSEAL GROWTH PLATE CALCIFIED CARTILAGE ZONE RESTING ZONE Loss of chondrocytes by apoptosis and calcification of Zone of Resting Cartilage 📣 cartilage matrix by hydroxyapatite crystals The “Normal” Hyaline Cartilage calcified cartilage zone is composed of empty cells Nothing much happens and functions only as an area where the chondrocytes rest ANATOMY Page 10 of 14  A.BONE GROWTH Always appositional with either endosteum or periosteum laying down lamellae of bone Always laid down on preexisting bone or cartilage Interstitial growth is impossible → Because of rigid ossified matrix does not allow osteocytes to divide or secrete additional matrix B. BONE REMODELING A continuous process of bone resorption and formation throughout life for growth or to mobilize calcium Ensures that bone tissue remains plastic and capable of adapting its internal structure in the face of changing Figure 46. Calcified Cartilage Zone of the Epiphyseal Plate [Lecturer’s PPT] stresses OSSIFICATION ZONE Maintains bone’s general shape while increasing its mass Where blood vessels and osteoblasts invade the → Example: Use of braces ; Braces apply constant lacunae of the chondrocytes traction to the bone which results to bone remodeling Bone tissue deposited on calcified cartilage and movement of teeth → Once the braces are removed, there is a shift of pressure ; The alveolar bone in the jaw is affected with results in the formation of a new bone on one side (deposition) and the renewal of the bone (resorption) on the other side → Happens to support the tooth / teeth in the movement STEPS IN BONE REMODELING The Osteoclasts attach themselves to the site of bone for resorption ↓ Formation of cavities (Resorption bay / Howship Lacunae) Figure 47. Ossification Zone of the Epiphyseal Plate [Lecturer’s PPT] tunnels ↓ Osteoblasts enters the newly formed tinner and line walls ↓ Osteoblasts secrete osteoid in a cyclic manner forming lamellae ; Osteocytes trapped in the lacunae ↓ Cavity is filled by lamellae until narrow central canal remains Figure 48. Epiphyseal Growth Plate (Histology Collection, Note: The remains of the partially resorbed osteons becomes UERMMMCI Department of Anatomy) [Lecturer’s PPT] the interstitial lamellae XII. CLINICAL APPLICATION A. OSTEOPOROSIS Common in the elderly which results in poor bone turnover where bone resorption is greater than bone formation that leads to calcium loss and reduced mineral content Bone becomes brittle and fragile which easily gets fractures Lack of exercise may lead to decreased bone density due to the lack of mechanical stimulation of the osteocytes or the mechanostat Figure 50. Steps in Bone Remodeling[Lecturer’s PPT] C. BONE REPAIR Osteoprogenitor stem cells in the periosteum, endosteum, and marrow Well-vascularized Figure 49. Normal Bone vs Osteoporotic Bone [Lecturer’s PPT] Excellent capacity for repair XIII. BONE GROWTH, REMODELING AND REPAIR ANATOMY Page 11 of 14  STEPS IN BONE REPAIR (FRACTURES) are noted. The breakdown of the nasal cartilage 1. Presence of fracture hematoma releases collagen fibers primarily of which type? a. Type I 2. The circulating macrophages remove the hematoma b. Type II 3. The fracture hematoma is converted to a procallus c. Type III (which is rich in collagen and fibroblast) d. Type IV 4. The procallus is invaded by blood vessels to provide e. Type VII nourishment to aid in bone repair/healing 6. Which component of bone impedes the distribution of 5. The soft procallus is replaced by a hard callus nutrients and oxygen to osteocytes? 6. Hard callus is transformed into a primary bone (woven a. ECM b. Canaliculi bone) by osteoblasts c. Periosteum 7. Woven bone is then replaced by a compact bone later on d. Cell processes e. Haversian canals Bone Healing – It takes about 6 to 8 weeks for bone to heal 7. Which if the following most accurately describes completely compact bone? Physiology Animations - Bone Repair a. Predominant bone type in the epiphyses of adult long bones b. Also known as cancellous bone c. Characterized by the presence of osteons d. Lines the medullary (marrow) cavity e. Forms the diploë in cranial bones 8. Which of the following most accurately describes the endosteum? a. Composed of two layers: osteogenic and fibrous b. Continuous with the joint capsule [Lecturer’s PPT] Figure 51. Steps in Bone Repair c. Attached to the bone surface by collagen bundles called Sharpey fibers XIV. REVIEW QUESTIONS d. Lines the medullary cavity 1. The molecular basis for the shock absorbing e. Contains mature osteocytes properties of cartilage involves which of the 9. Which “zone” of endochondral ossification in the following? growing femur of an adolescent is the farthest from a. Electrostatic interaction of proteoglycans with type IV that bone’s secondary ossification center? collagen a. Zone of hypertrophy b. Ability of glycosaminoglycans to bind anions b. Zone of reserve cartilage c. Noncovalent binding of glycosaminoglycans to protein c. Zone of calcified cartilage cores d. Zone of ossification d. Sialic acid residues in the glycoproteins e. Zone of proliferation e. Hydration of glycosaminoglycans 10. The major lubricant for diarthrotic joints is 2. Which feature is typical of elastic cartilage? synthesized by cells located in which joint structure? a. Primary skeletal tissue in the fetus a. Nucleus pulposus b. No identifiable perichondrium b. Synovial membrane c. Found in intervertebral discs c. Articular cartilage d. Most widely distributed cartilage type in the body d. Annulus fibrosus e. Collagen is mainly type II e. Fibrous capsule 3. How does articular cartilage differ from most other hyaline cartilage? a. It undergoes mainly appositional growth. ANSWER KEY b. It contains isogenous groups of chondrocytes. 1. E Its semi-rigid consistency is attributable to water c. It lacks a perichondrium. bound to the negatively charged hyaluronan d. Its matrix contains aggrecan. and GAG chains extending from proteoglycan 4. Which step occurs first in chondrogenesis? core proteins, which in turn are enclosed within a. Appositional growth a dense meshwork of thin Type II collagen b. Conversion of chondroblasts to chondrocytes fibrils. The high content of bound water allows c. Formation of mesenchymal condensations cartilage to absorb impact with minimal damage d. Interstitial growth to its structure. e. Secretion of collagen-rich and proteoglycan-rich matrix 2. E 5. A 28-year-old woman visits the family medicine clinic complaining of loss of the sense of smell, nosebleeds, problems with swallowing, and hoarseness. She admits to “casual, social use” of cocaine on a regular basis since her sophomore year of college. A complete examination of her nose with a speculum and otoscope shows severe rhinitis (inflammation). There is also perforation and collapse of the nasal cartilage resulting in a “saddle nose” deformity. Erosions in the enamel of her front teeth ANATOMY Page 12 of 14  3. C All hyaline cartilage is covered by XV. REFERENCES perichondrium except in the articular 2026 (2022). Transcription. cartilage of joints. Buñing, M.C. (2021). Bone and Cartilage. [Recorded Lecture] 4. C The first indication of cell differentiation is the Lecturer’s PPT rounding up of the mesenchymal cells. Mescher, A. L. (2018). Junqueira's Basic Histology Text and Atlas (15th ed.). McGraw-Hill Education. Mesenchyme is the precursor for all types of cartilage. 5. B Nasal cartilage is of the elastic type. Elastic cartilage is primarily composed of Type II collagen. 6. A The ECM of the bone is not as permeable as the ECM of the cartilage, thus necessitating the presence of canaliculi and perforating canals. The rigidity of the bone ECM also prevents osteocytes from having mitotic activity. 7. C Compact bone is composed of osteons, while trabecular bone is composed of trabeculae, sponge-like structures. 8. D A and C refer to the periosteum. B refers to the synovial membrane. D refers to lacunae, cavities occupied by the osteocytes in the bone matrix. 9. D Secondary ossification centers form in epiphyses around the time of birth. The ossification proceeds from the diaphysis towards the distal and proximal epiphyses. 10. B The synovial membrane has specialized cells that produce hyaluronan and proteoglycans that form the synovial fluid. ANATOMY Page 13 of 14  XVI. APPENDIX Table 1. Important features of cartilage parts ANATOMY Page 14 of 14