Workshop_Bone_and_Bone-Formation_Fall_2023 (1).pptx

Workshop Bone and Bone Formation Fall 2023 Dr. Mhawi [email protected] Piont Solution Session ID: amir1 https://www.surveymonkey.com/r/T9Y DN82 •• If you have technical difficulties during the session that you cannot solve in a few minutes, please email [email protected] at the time of the diffic...

Workshop Bone and Bone Formation Fall 2023 Dr. Mhawi [email protected] Piont Solution Session ID: amir1 https://www.surveymonkey.com/r/T9Y DN82 •• If you have technical difficulties during the session that you cannot solve in a few minutes, please email [email protected] at the time of the difficulty to have your situation logged. Ensure that you clearly indicate your course and the specific activity you are having difficulty with if you would like this to be effective.” •• For assistance with any technical or connectivity issues, students can always message [email protected] Piont Solution Session ID: amir1 https://www.surveymonkey.com/r/T9Y DN82 Q1. False or true? Like chondrocytes, osteocytes are prone to live within isogenous groups to facilitate communications with each other. A. False B. True https://www.surveymonkey.com/r/T9Y DN82 Piont Solution Session ID: amir1 :50 Bones: General Features • Mineralized matrix contains spaces called Lacunae • Each houses an OSTEOCYTE • Osteocyte sends numerous processes into microscopic tunnels called CANALICULI • Canaliculi run through mineralized matrix • Connect adjacent lacunae • Allow contact between cell processes of neighboring osteocytes • Processes of osteocytes communicate via gap junctions (blue arrows) • To transfer oxygen and ions bone ca n al ic ul bone canaliculi lacuna us osteocyte canaliculi lacuna Classification of bones • Compact bone (dense) • Found in the outer region (black arrows in the photograph) • Contains no bone marrow • Spongy (cancellous/trabecular) • Situated on the inside forming meshwork of spicules or trabeculae spicules • Spaces between meshwork is filled with bone marrow and blood vessels Bone marrow Q2. Which of the following most accurately describes the periosteum? A. Firmly attached to the bone surface by hemidesmosomes B. Continuous with the endosteum C. Firmly attached to the bone surface by collagen bundles called Sharpey’s fibers D. Lines the bone marrow-filled cavities E. Contains mature osteocytes :50 Periosteum: Periosteum and Endosteum IC Bone osteobla sts Bone marrow cavity bone Endosteal (osteoprogenitor) cells Bone marrow cavity bone periosteum • Often one cell-thick layer of flattened cells OF Sharpey’s Endosteum: periosteum fibers • Dense connective tissue • Covers the outer surfaces of the bone • Consists of two layers • Outer fibrous (OF)- contains type 1 collagen fibers • Collagen fibers entert into the bone matrix • Called Sharpey’s fibers • Inner layer (IC)- contains osteoprogenitor cells • Osteoprogenitor cells can differentiate into osteoblasts when stimulated (during the growth of the bone or fracture) Structure of Mature Compact Bone • Composed of structural units called • HAVERSIAN SYSTEMS (OSTEONS) • Cylindrical units of compact bone • Consist of concentric lamellae of matrix around a central canal • AKA the HAVERSIAN CANAL • Canal contains vascular and nerve supply of the osteon • Lined with endosteal/osteoprogenitor cells Haversian canal Endosteal/osteooprogenitor cell Structure of Mature Spongy Bone Bone marrow • Very similar to mature compact bone except • Bone matrix is arranged as SPICULES or TRABECULAE • With numerous interconnecting bone marrow spaces Bone marrow spicul e Bone marrow spicule Bone marrow • Trabeculae will develop into OSTEONS (Haversian system) if they are sufficiently thick (Rectangle in the lower image) Bone marrow Bone marrow Structure of Immature (Woven) Bone Bones initially formed in the skeleton of a developing fetus are called immature bone Compare immature (woven) bone with mature (lamellar) bone Immature mature (lamellated) bone (woven) bone Bone matrix is not lamellated Because of the interlacing arrangement of Contains more cells per collagen fibers unit area Matrix has more ground substance Bone matrix is lamellated Contains less cells per unit area Matrix has less ground substance Q3. Which of the following best describes Volkmann’s canals? A. Channels that are found within the compact bones and lined by periosteal cells B. Channels connecting Haversian canals with each other C. Channels that are filled with type I collagen fibers D. Channels that are run parallel to the Haversian canal E. They are spaces filled with bone marrow :75 • VOLKMANN’S CANALS (AKA perforating canals) • Found in lamellar bone • Connect Haversian canals to each other • Lined by osteoprogenitor cells • Through which blood vessels and nerves travel from periosteal and endosteal surfaces to reach the Haversian canal Cross section of Haversian canal Cross section of Haversian canal longitudinal section of Volkmann's canal Haversian canal longitudinal section of Volkmann’s canal Haversian canal Q4. Osteoid is unmineralized bone matrix deposited by which of the following cells? A. Osteocytes B. Osteoprogenitor cells C. Osteoblasts D. Osteoclasts E. Mesenchymal cells :75 Cells of the Bone On the bone surfaces (outside the bone matrix) Inside the bone matrix Osteoprogenitor cells Osteocytes Osteoblasts Osteoclasts Osteoprogenitor cell osteoclasts Bone marrow osteocytes Bone marrow osteoblasts Bone spicule Oste oid • Osteoblasts deposit unmeniralized bone matrix called OSTEOID • Appears as lightly stained area between the osteoblasts and the previously formed bone • Osteoid is rich in: • Type I collagen • Osteocalcin and osteonectin calcium- and phosphate-binding proteins • Raise local Ca++ and PO4--- conc. • Alkaline phosphatase (ALP) • Responsible for the crystallization of CaPO4 around the type 1 collagen B, bone; M, mesenchyme; Ob, osteoblast; Oc, osteocyte; Os, osteoid (between the blue arrows). Q6. Bones undergo continuous remodeling. A process that aims to protect the structural integrity of the skeletal system and metabolically contributes to the body's balance of calcium and phosphorus. Remodeling entails the resorption of old or damaged bone, followed by the deposition of new bone material. In healthy bones, which of the below two cells collaborate with each other to achieve the process of balanced bone remodeling? A. Osteocyte and osteoblast B. Osteoblast and osteoprogenitor cell C. Osteocyte and osteoclast D. Osteoblast and osteoclast E. Osteocyte and osteoprogenitor cell F. Osteocytes and mesenchymal cells :75 Bone Remodeling of Compact Bone Depends on the Collaborative Cellular Activities of Osteoclast and Osteoblast • Osteoclasts bore a tunnel (approx.200 µm in diameter) called the resorption cavity, through compact bone • Blood vessels and their surrounding connective tissue occupy the tunnel. • The tunnel consists of two parts: • The tip is called the cutting cone • consists of advancing osteoclasts • Cutting cone is followed by the closing cone • Consists of osteoblasts • Osteoblasts begin to deposit the osteoid on the walls of the tunnel in successive lamellae • As successive lamellae of bone are deposited, the tunnel ultimately attains the relatively narrow diameter of the mature Haversian canal lined by endosteal cells • With time, the bone matrix in each of the lamellae becomes mineralized • In healthy adults, 5%-10% of the bone turns over annually Bone remodeling 2 3 1 Section of mature lamellar bone showing different generations of bone 2 3 Diagram showing the bone remodeling and the different stages of mineralization First generation of bones = old 1 X-ray micrograph of bone showing bone remodeling and stages of mineralization Q5. ID the structures identified by the question mark in the accompanying x-ray micrograph of bone tissue? A. Fourth generation of bone remodeling B. Haversian canal C. Newly formed resorption cavity D. Volkmann’s canal E. Bone marrow-filled cavities :75 Q7. Which health condition is expected to happen if, during the bone remodeling, the collaboration between the osteoblast and osteoclast becomes imbalanced due to the inhibition of the osteoclast? A. Osteomalacia B. Osteoporosis C. Dwarfism D. Osteopetrosis E. Achondroplasia :75 Bone Formation Bones are formed by two mechanisms 1, Intramembranous bone formation Bones formed by this mechanism are Flat bones of skull and face as well as the clavicle bone Endochondral ossification 2, Endochondral bone formation Bones formed by this mechanism are long bones and Intramembranous ossification Intramembranous Bone Formation Begins at 8th week of gestation Mesenchymal cells migrate to site where flat bones are to be formed and aggregate into a bone blastema Blastema cells are interconnected by their cytoplasmic processes and the area becomes more vascularized Cells of the blastema differentiate into osteoblasts Osteoblasts lay down bone matrix and bone spicules start to form Spicules formation continues until spongy (cancellous) bone is formed Spicules of the spongy bone surround bone marrowfilled spaces Bone marrow-filled spaces are vascularized and lined by endosteal cells Endosteal cells differentiate into osteoblasts Osteoblasts deposit consecutive layers of bone The filling of the marrow space with consecutive layers of bone continues until Haversian systems, each with a central canal containing blood vessel is created This is how the spongy/trabecular bone is remodeled into compact bone of the surface of the dura matter that contacts the inner surface of the skull bone. Dura matter is one of three layers of connective tissue that cover the brain and spinal cord, collectively called the meninges. Dura matter consists of two layers, the periosteal and meningeal layers (shown in blue in the accompanying image). She found that the periosteal layer of the dura matter is absent each time the calvarium is removed from the cadaver. Which of the following contributes to the absence of the periosteal layer of the dura? A. Periosteal dura disintegrates when the calvarium is removed B. Periosteal dura is disolved when bombarded by the electros of the microscope C. Periosteal dura should be fixed properly before the removal of the calvarium D. Periosteal dura is attached by Sharpey’s fibers firmly to the periosteum of the :75 calvarium Endochondral Bone Formation Collar bone Chondrocyte perichondrium • Starts at 12 weeks of gestation in primary ossification center (midsection of the cartilage model) • Hyaline cartilage model forms first and acquires the general shape of the future bone • First sign of bone formation is the appearance of cuff of bone (AKA collar bone) around the primary ossification center of cartilage model • Formation of Cuff bone causes hypertrophy of chondrocytes at the primary ossification center • Cartilage extracellular matrix (in black) calcifies causing the death of the chondrocytes • Blood vessels (AKA periosteal bud) accompanied by osteogenic (periosteal) cells, grow through the thin collar bone to vascularize the primary ossification center • Osteogenic cells migrate into the cavities along with blood vessels, attach to the calcified cartilage spicules, and differentiate into osteoblasts • Osteoblasts deposit new bone matrix on the surface of the calcified cartilage matrix creating mixed spicules • Toward the end of gestation, long bones consist of ossified diaphysis (made of cancellous bone) and cartilaginous epiphyses • Postnatally, most of the long bones exhibit secondary ossification centers at each epiphysis • Hyaline cartilage is left only at the articular surfaces and at the epiphyseal growth plates of the long bones Q9. During the growth period long bones undergo continuous widening until they reach their final diameter. (i) which of the following significantly contributes to the widening of the long bones and (ii) by which mechanism? A. (i) Calcified extracellular matrix of the cartilage, (ii) deposition of Ca+ + and PO4 B. (i) Osteocytes, (ii) deposition of type I collagen C. (i) Periosteum, (ii) appositional growth D. (i) Hyaline cartilage of the epiphyseal growth plate, (ii) endochondral bone formation E. (i) Endosteum, (ii) interstitial growth :75 Lengthening of Long Bones • Lengthening of long bone depends on the presence to the epiphyseal growth plate • Under the influence of growth hormones • Composed of five zones (from the epiphysis to the diaphysis): 1- Resting (reserve) zone: chondrocytes are not dividing 2- Proliferative zone: - Highly dividing chondrocytes - Arrange in columns - Secrete matrix 3- Hypertrophy zone: chondrocytes becomes hypertophic and compress the matrix 4- Calcification zone: matrix calcifies, chondrocytes die, and removed leaving spicules of calcified matrix 5- Ossification zone: - Blood vessels from the bone marrow invade the zone and bring osteoprogenitor cells (differentiate into osteoblasts) - Osteoblasts lay down new bone (osteoid) on the clacified cartilage matrix Resting zone Proliferative zone Hypertrophy zone Calcification zone Ossificaion zone Q10. Fales or true? Lengthening of the long bone during the growth period depends on the interstitial and the appositional growth of the hyaline cartilage of the epiphyseal growth plate. A. Fale B. Ture :75