[HISTO]LEC_008_BONE-AND-CARTILAGE.pdf

(008) BONE AND CARTILAGE DR.LA PAZ LUCERO-PEREDO | 10/19/2020 OUTLINE III. BONE CELLS I. OVERVIEW II. BONE MATRIX...

(008) BONE AND CARTILAGE DR.LA PAZ LUCERO-PEREDO | 10/19/2020 OUTLINE III. BONE CELLS I. OVERVIEW II. BONE MATRIX  3 Major Cell Types 1. Osteoblasts III. BONE CELLS 2. Osteocytes A. Osteblasts 3. Osteoclasts B. Osteocytes C. Osteoclasts A. OSTEOBLASTS -”Osteon” - bone + “blastos”- germ IV. COVERINGS OF THE BONE - these are growing cells that synthesize, secrete A. Periosteum organic components of the matrix: B. Endosteum a. Collagen type 1 V. TYPES OF BONES b. Proteoglycans c. Glycoproteins VI. OSTEOGENESIS -Located exclusively at the surface of bone matrix VII. BONE GROWTH REMODELLING AND bounded by integrins forming single layer of REPAIR cuboidal cells VIII.CARTILAGE -Osteoblasts differentiate to either as osteocytes entrapped in matrix-bound lacunae, some flatten and A. Hyaline Cartilage cover the matrix surface as bone lining cells, and B. Elastic Cartilage majority undergo apoptosis C. Fibrocartilage  Osteosarcoma- arise in osteoprogenitor cells (germ cells I. OVERVIEW -Primary bone tumors,  Bone originating directly from -forms the skeletal system bone cells, but these are -Specialized connective tissue composed of bone matrix uncommon and bone cells -Provides support for the body -Usually more of a metastatic tumors, -Protects vital organs (I.e Cranial and Thoracic cavities) arising when cancer cells move -Reservoir of Ca, PO4, and other ions/metabolites into bones from malignancies in -Also forms a system of levers that multiply the forces other organs (I.e Breast cancer generated during contraction and transform them into spreads throughout the body, bodily movements including the bone)  Composition Note: When it is a primary bone tumor, it came from A. Bone Matrix osteoblasts B. Bone Cells II. BONE MATRIX -Calcified extracellular material  Composed of: 1. Inorganic Matter - 50%; Ca hydroxypatite is most abundant, Mg, K, Na, Amorphous CaPO4 2. Organic Matter - type 1 collagen, proteoglycans, glycoproteins (bone specific multiadhesive osteonectin; osteocalcin calcium-binding proteins from Fig 1. Bone histology (Microscopic). Where (Ob) is matrix vesicles promotes osteoblasts, (Ocl) is osteoclasts and (Oc) are the calcification) osteoscytes. PREPARED AND EDITED BY: PADOLINA, J.  (008) BONE AND CARTILAGE DR.LA PAZ LUCERO-PEREDO | 10/19/2020 -Essential for matrix resorption (removing the calcified bone) during bone growth and remodeling -Osteoclasts lie within cavities in matrix (Resorption cavities or Howship lacunae) -During resorption, surface against bone matrix is folded into irregular projections, ruffled border, surrounded by cytoplasmic zone creating environment for resorption.  Osteopetrosis- genetic disease with dense heavy bones, “marbled bones” -Osteclasts lack ruffled borders, causing defect in bone resorption, resulting in Fig 2. Bone Histology (illus.) overgrowth, thickening of bones,often with obliteration of marrow cavities, depressing blood cell formation, causing B. OSTEOCYTES anemia and loss of WBC -”Osteon”- Bone + “Kytos”- cell  Osteoporosis- frequently found in immobilized -Enclosed singly within lacunae spaced throughout patients, postmenopausal women, matrix, extend many long dendritic processes resorption exceeds bone formation occupying many canaliculi radiating from lacuna to leading to calcium loos from bones, lacuna (lacunar-canalicular network) reduced bone mineral density (BMD) -Their dendritic process also acts as mechanosensors detecting mechanical load on bone as well as stress, fatigue-induced microdamage (Mechanostat) -Most abundant cells in bone  Mechanostat- monitor mechanical loads within bones and signal cells to adjust bone matrix; exercise bone density -when there is an exercise, it increases the bone density Fig 4. Osteocytes. Where there are multiple nucleus in it,as well as ruffled borders. Fig 3. Osteocytes. The osteocytes are located inside a cavity and it has processes connecting to each other that sends signal to each other when there is stress or damage to the bone. C. OSTEOCLASTS -“Osteon”- Bone + “Klastos”- broken -Giant motile, multinucleated cells involved in removing calcified bone matrix and remodeling bone tissue Fig 5. Illustration of octeocytes PREPARED AND EDITED BY: PADOLINA, J.  (008) BONE AND CARTILAGE DR.LA PAZ LUCERO-PEREDO | 10/19/2020 IV. COVERINGS OF THE BONE b. Diaphysis- compact bone with thin region of spongy bone in inner surface, around central A. PERIOSTEUM marrow cavity - External connective tissue covering of the bone -The Outer layer- dense connective tissue the consists of blood vessels, collagen bundles called perforating fibers or sharpey, fibroblasts, blood vessels -The Inner layer- the more cellular layer, consists of osteoblasts, mesenchymal stem cells called osteoprogenitor cells -Due to the abundance or osteoprogenitor cells, as well as blood vessels and others, bone can easily repair itself. B. ENDOSTEUM -inner covering of the bone -thinner than periosteum -contains osteoprogenitor cells, osteoblasts, bone lining cells, collagen fibers Fig 6. Compact bone and cancellous bone. Compact bone is seen in the external part of the bone and supports the cancellous bone. V. TYPES OF BONE  Compact (cortical) Bone- dense area near surface -80% of total bone mass -Thick outer region of bones beneath periosteum -Parallel lamellae or densely packed osteon  Cancellous (trabecular or spongy)- deeper area with numerous interconnecting cavities -adjacent to marrow cavities -Interconnected trabecular covered by endosteum -20% of total bone mass  Lamellar bone- most bone in adults, organized as lamellar bone, by layers or lamellae, parallel to each other or concentrically around a central canal (Osteon or Haversian canal) -Each osteon canal also communicate with one another through transverse perforating canals (or Volkmann canals)  Woven bone- nonlamellar, random disposition of type 1 collagen fibers -1st bone tissue to appear in embryonic development and in fracture repair -temporary, replaced in adults by lamellar except in calvaria -lower mineral content -more osteocytes- form more quickly but has less Fig 7.1 and 7.2. Lamellar bone. They are arranged concentrically layerd by layer with the central canal in the center wherein the blood vessels are strength than lamellar bone located. These are called the Haversian system or osteons The bone is divided into: a. Epiphyses- bulbous ends in long bones, spongy VI. OSTEOGENESIS bone covered by thin layer of compact -Bone development bone PREPARED AND EDITED BY: PADOLINA, J.  (008) BONE AND CARTILAGE DR.LA PAZ LUCERO-PEREDO | 10/19/2020  Intramembranous Ossification- Osteoblasts differentiates VII. BONE GROWTH, REMODELLING, AND directly from mesenchyme and begin secreting osteoid, REPAIR by which most flat bones begin to form -Most bones of the skull and jaws, as well as the -Bone has excellent capacity for repair because it contains scapula and clavicle, are formed embryonically by osteoprogenitor stem cells, the periosteum, endosteum, intramembranous ossification. and marrow, and is very well vascularized -The rate of bone turnover is very active in young children,  Endochondral ossification- preexisting matrix of hyaline where it can be 200 times faster than that of adults. I cartilage eroded and invaded by osteoblasts then begin osteoid production - This type of ossification forms most bones of the body and is especially well studied in developing long Bone Fracture repair: bones  1. Hematoma formation  Primary Ossification Center- Diaphysis, 1st trimester 2. Fibrocartilaginous/soft callus formation  Secondary Ossification Center- Epiphyses, time of birth 3. Endochondral ossification 4. Hard callus formation of woven bone 5. Remodelling 6. Woven bone is replaced by lamellar bone Fig 8. Intramembranous ossification. Develops through the mesenchyme, distant from the osteoblast. Osteoblast then directly forms the osteoid. Fig 10. Bone Fracture repair. VIII. CARTILAGE -Tough, flexible form of connective tissue characterized by extracellular matrix, proteoglycans, collagens, and elastic fibers -Consists of cells, chondrocytes embedded in extracellular matrix -Has firm consistency, allows tissue to bear mechanical stress without permanent distortion -Provide shock absorbing and sliding regions with joints and facilitates bone movements Fig 9. Development of the bone. Chondrocytes- cells in the cartilage, embedded in the ECM  Epiphyseal Cartilage/ Epiphyseal plate/ Growth plate- which unlike connective tissue -Connects epiphysis to diaphysis, resposible for growth in length of bone, disappears at Three types of Cartilages: adulthood causign bone growth to cease A. Hyaline cartilage -Epiphyseal closure is complete by age of 20 (“Bone B. Elastic cartilage age” in forensics) C. Fibrocartilage  Articular Cartilage- usually persists through adult life, but does not contribute to bone growth -where we usually test for osteoarthritis -”The wear and tear cartilage” PREPARED AND EDITED BY: PADOLINA, J.  (008) BONE AND CARTILAGE DR.LA PAZ LUCERO-PEREDO | 10/19/2020 A. HYALINE CARTILAGE C. FIBROCARTILAGE -the most common form -Combination of hyaline cartilage and dense -in adults, it is located in articular surfaces of movable connective tissue joints, ventral ends of ribs, epiphyseal plate of long -Consists of small chondrocytes in hyaline matrix bones, wall of respiratory passages usually layered with larger area of bundled type I -ECM is homogenoeus and glassy, rich in fibrils of type II collagen scattered fibroblasts collagen and aggregate complexes with bound water -Present in body regions subjected to pulling forces -ECM has less collagen and more proteoglycans -Intervertevral discs, pubic symphisis -Perichondrum is usually present, but not at the hyaline -Act as cushions and shock absorbers cartilage of articular surface of the epiphysis of growing long bones Fig 13. Fibrocartilage. Same as hyaline, it has individual cells, however it contains more connective tissues in between. Fig 11. Hyaline cartilage. B. ELASTIC CARTILAGE -Possesses abundant elastic fibers in addition to collagen type 11 -Provides flexible shape and support of soft tissues -Auricle of the ear, epiglottis, larynx -Generally resemble hyaline cartilage in chondrocytes and ECM components but matrix inclued abundant elastic fibers which increased tissue flexibility -Always surrounded by perichondrium Fig 14. Location of the cartilages in the body Fig 12. Elastic Cartilage. Has more elastic cartilage in between PREPARED AND EDITED BY: PADOLINA, J.  (008) BONE AND CARTILAGE DR.LA PAZ LUCERO-PEREDO | 10/19/2020 REFERENCES Doc Peredo’s Lecture Mescher A L. (2016) Junquiera’s Basic Histology: Text and Atlas. McGraw Hill Education: NY Fig 15.1. Hyaline Cartilage Fig 15.2 Fibrocartilage Fig 15.3 Elastic cartilage PREPARED AND EDITED BY: PADOLINA, J.  (008) BONE AND CARTILAGE DR.LA PAZ LUCERO-PEREDO | 10/19/2020 Appendix 1 Appendix 2 PREPARED AND EDITED BY: PADOLINA, J.