St. George's University MSK Lecture 19 - Histological Classification and Organization of Bone PDF

Basic Principles of Medicine 1 Module: Musculoskeletal System | Lecture 19 Histological Classification and Organization of Bone Dr. Ali Drigo [email protected] Department of Anatomical Sciences School of Medicine, St. George’s Univ...

Basic Principles of Medicine 1 Module: Musculoskeletal System | Lecture 19 Histological Classification and Organization of Bone Dr. Ali Drigo [email protected] Department of Anatomical Sciences School of Medicine, St. George’s University  Copyright All year-1 course materials, whether in print or online, are protected by copyright. The work, or parts of it, may not be copied, distributed, or published in any form, printed, electronic, or otherwise. As an exception, students enrolled in year 1 of St. George’s University School of Medicine and their faculty are permitted to make electronic or print copies of all downloadable files for personal and classroom use only, provided that no alterations to the documents are made and that the copyright statement is maintained in all copies. ‘View only’ files, such as lecture recordings, are explicitly excluded from download, and creating copies of these recordings by students and other users is strictly illegal. BMP1 | MSK | Lecture 19 | Bone I The author of this document has made the best effort to observe current copyright law and the copyright policy of St. George's University. Users of this document identifying potential violations of these regulations are asked to bring their concerns to the attention of the author.  Recommended Reading Histology – A Text and Atlas Pawlina 9th Edition Chapter 8: Bone Bone | Histology: A Text and Atlas: With Correlated Cell and Molecular Biology, 9e | Premium Basic Sciences | Health Library (lwwhealthlibrary.com) BMP1 | MSK | Lecture 19 | Bone I  Your Objectives will show here! Objectives Describe bone as a specialized connective tissue in terms of its cells, fibers and ground SOM.MK.I.BPM1.1.FTM.3.HCB.0212 substance. SOM.MK.I.BPM1.1.FTM.3.HCB.0213 List the major components of bone extracellular matrix and their significance. Identify & describe the structure, function and localization of the cells of bone tissue SOM.MK.I.BPM1.1.FTM.3.HCB.0214 including osteoprogenitor cell, osteoblast, osteocyte and osteoclast. SOM.MK.I.BPM1.1.FTM.3.HCB.0215 Identify & describe the structure, function and localization of periosteum. SOM.MK.I.BPM1.1.FTM.3.HCB.0216 Identify & describe the structure, function and localization of endosteum. SOM.MK.I.BPM1.1.FTM.3.HCB.0217 Compare and contrast immature bone vs. mature bone. SOM.MK.I.BPM1.1.FTM.3.HCB.0218 Compare and contrast spongy bone vs. compact bone. SOM.MK.I.BPM1.1.FTM.3.HCB.0219 Define an “osteon” and describe its normal development SOM.MK.I.BPM1.1.FTM.3.HCB.0220 Define “osteoid”. BMP1 | MSK | Lecture 19 | Bone I SOM.MK.I.BPM1.1.FTM.3.HCB.0221 State the origin of osteoclasts. SOM.MK.I.BPM1.1.FTM.3.HCB.0222 Describe the structure of the osteoclast in relation to its function. Identify & describe the structures of compact bone including osteon, concentric lamellae, Haversian canal, outer & inner circumferential lamellae, interstitial lamellae and SOM.MK.I.BPM1.1.FTM.3.HCB.0223 Volkmann’s canal. SOM.MK.I.BPM1.1.FTM.3.HCB.0224 Describe the function of canaliculi. SOM.MK.I.BPM1.1.FTM.3.HCB.0225 Describe the process of “ground bone preparation” to study the structure of compact bone.  SOM.MK.I.BPM1.1.FTM.3.HCB.0212 Bone Specialized Connective tissue composed of cells and calcified extracellular matrix (ECM) The cells and calcified ECM form a rigid organ BMP1 | MSK | Lecture 19 | Bone I Session ID: histobone  SOM.MK.I.BPM1.1.FTM.3.HCB.0213 Functions of Bone Hematopoiesis – the formation of blood cells from hematopoietic stem cells found in the bone marrow. Lipid and mineral storage – bone is a reservoir holding adipose tissue within the bone marrow and calcium within the hydroxyapatite crystals. Support – bone forms scaffolding for skeletal muscle and other soft tissues, it creates a framework that gives the general shape of the body. BMP1 | MSK | Lecture 19 | Bone I Protection – particularly the axial skeleton which surrounds the major organs of the body.  SOM.MK.I.BPM1.1.FTM.3.HCB.0213 Components of Bone 1. The Extracellular matrix: (ECM) refers to the molecules that provide biochemical and structural support to the cells that populate bone. Organic portion is predominantly (90% of total weight of matrix proteins) composed of collagenous proteins Fibers: mainly type I collagen (also type V, III, XI, XIII). Ground substance: non-collagenous proteins (about 10% of matrix proteins) - include proteoglycans, glycoproteins, bone specific proteins, growth factors and cytokines Essential to bone development, growth, remodeling, and repair Both the collagen fibers and ground substance become mineralized to form bone tissue BMP1 | MSK | Lecture 19 | Bone I Inorganic portion represents about 50% of the dry weight of the matrix and is composed mainly of calcium phosphate in the form of hydroxyapatite crystals Contains trace minerals such as bicarbonate, citrate, magnesium, potassium and sodium  SOM.MK.I.BPM1.1.FTM.3.HCB.0214 Components of Bone (cont.) 2. Cells of bone tissue: Osteoprogenitor (osteogenic) - the stem cells of bone, derived from primitive mesenchymal cells. - differentiate into osteoblasts Osteoblasts - Synthesize uncalcified/unmineralized extracellular matrix called osteoid (later becomes calcified/mineralized to form bone) Osteocytes - As the osteoid mineralizes, the osteoblasts become entombed between lamellae in lacunae where they mature into osteocytes. They then monitor the minerals and proteins to regulate/maintain bone mass. Osteoclasts - Multinucleated giant cells derived from monocyte progenitor cells responsible for resorbing and remodeling bone by releasing H + ions and lysosomal BMP1 | MSK | Lecture 19 | Bone I enzymes. The balance of osteoblast to osteoclast activity is crucial in the maintenance of the tissue’s structural integrity. It also plays a role in conditions such as osteoporosis. Bone-lining cells - Found on the inner and outer surface of bone; The endosteum and periosteum  SOM.MK.I.BPM1.1.FTM.3.HCB.0214 Cells of Bone Tissue BMP1 | MSK | Lecture 19 | Bone I  SOM.MK.I.BPM1.1.FTM.3.HCB.0214 Identification of Cells of Bone Tissue Look for: 1) Osteoblasts: cuboidal cells located on the BV periphery of bone. Displays 1 euchromatic nuclei with a 3 basophilic cytoplasm. 2 2) Osteocytes: mature osteoblasts entrapped in bony matrix. 3) Osteoclasts: BMP1 | MSK | Lecture 19 | Bone I large, multinucleated macrophages located along the endosteum  SOM.MK.I.BPM1.1.FTM.3.HCB.0214 Bone Cells Osteogenic/osteoprogenitor cells Derived from embryonic mesenchyme stem cells in the bone marrow Found on the external and internal surfaces of bones (may also reside in the microvasculature supplying bone). Morphologically, they resemble the periosteal/ endosteal cells. Can differentiate into osteoblasts. In growing bones- appear as BMP1 | MSK | Lecture 19 | Bone I flattened or squamous cells with lightly staining, elongate, or ovoid nuclei and inconspicuous acidophilic or slightly basophilic cytoplasm. Ob: osteoblast Op: osteoprogenitor cell  SOM.MK.I.BPM1.1.FTM.3.HCB.0214 Osteoblasts Derived from osteoprogenitor cells Osteoblasts Basophilic (active) Morphologically Calcified matrix Cuboidal (high secreting activity) OR Flattened/attenuated (declining secretions) Aggregate into a single layer of cells lying in apposition to the forming bone BMP1 | MSK | Lecture 19 | Bone I Cytoplasmic processes contact them with other osteoblasts and osteocytes  SOM.MK.I.BPM1.1.FTM.3.HCB.0214 Osteoblasts During synthesis, osteoblasts have well developed RER and Golgi apparatus PAS positive granules in the cytoplasm are most likely the precursors of glycosaminoglycans (of the osteoid matrix) Eventually matrix secretion entraps the osteoblast in a lacunae with its cytoplasmic processes extending into canaliculi Can secrete osteoclast stimulating factor BMP1 | MSK | Lecture 19 | Bone I Osteoblast eventually ceases its secretory function, undergoes changes to its morphology and becomes an osteocyte  SOM.MK.I.BPM1.1.FTM.3.HCB.0214 Osteocytes Mature bone cells, derived from osteoblasts Housed in their own lacunae Maintain communication and exchange nutrients and ? metabolites via gap junctions between their narrow cytoplasmic processes (filopodia) extending through the Osteocyte canaliculi s Increased amounts of condensed nuclear chromatin, BMP1 | MSK | Lecture 19 | Bone I reduced amounts of RER and a smaller Golgi apparatus vs osteoblasts  SOM.MK.I.BPM1.1.FTM.3.HCB.0225 Ground bone preparations SOM.MK.I.BPM1.1.FTM.3.HCB.0224 Bone samples are ground to near translucency using mechanical attrition Haversian canals No organic components of bone remain after grinding The tissue is then C L impregnated with India ink. BMP1 | MSK | Lecture 19 | Bone I L C L: lacunae L C: canaliculi  SOM.MK.I.BPM1.1.FTM.3.HCB.0214 Compare and contrast Osteoblast Osteocyte Resorptive Osteocyte BMP1 | MSK | Lecture 19 | Bone I MM – mineralized matrix, OL – osmiophilic lamina, M – mitochondria, L – lysosomes, G – Golgi apparatus  SOM.MK.I.BPM1.1.FTM.3.HCB.0214 Osteoclasts SOM.MK.I.BPM1.1.FTM.3.HCB.0221 Multinucleated giant cells (up to 50 nuclei) resulting from the fusion of hematopoietic monocyte progenitor cells Howship’s lacunae (resorption bays) are H&E stain depressions on the bone surface that house osteoclasts Lacunae result from the BMP1 | MSK | Lecture 19 | Bone I osteolytic activities of osteoclasts  SOM.MK.I.BPM1.1.FTM.3.HCB.0222 Osteoclasts Three distinct regions: 1. Ruffled Border Finger-like evaginations Osteoclast along Howship’s lacunae depict sites of active bone resorption Basal region Lysosome 2. Clear Zone Region of cytoplasm that surrounds the ruffled border Clear Microfilaments, anchor zone osteoclast to the boney surface and help isolate Ruffled BMP1 | MSK | Lecture 19 | Bone I osteoclastic activity border 3. Basal region Houses the organelles and Bone matrix numerous nuclei of the cell  SOM.MK.I.BPM1.1.FTM.3.HCB.0222 Osteoclasts - Bone Resorption Lysosomal enzymes (from Golgi complex) and hydrogen ions released into the confined Osteoclast space between bone matrix and the osteoclast’s peripheral clear zone Basal Acidic environment provides region optimal pH for activity of Lysosome lysosomal hydrolases and facilitates the dissolution of calcium phosphate from bone Clear zone Decalcified bone matrix is then Ruffled BMP1 | MSK | Lecture 19 | Bone I broken down by acid border hydrolases, collagenous and proteolytic enzymes and the cell resorbs the organic and Bone matrix inorganic material  SOM.MK.I.BPM1.1.FTM.3.HCB.0214 Bone-lining cells Osteoblast derived flat cells with little cytoplasm and scant organelles Found on the outer (periosteal cells) and inner (endosteal cells) surface of non-remodeling bone Function in maintenance and nutritional support of underlying cells Regulate movement of phosphate and calcium into and out of bone BMP1 | MSK | Lecture 19 | Bone I  SOM.MK.I.BPM1.1.FTM.3.HCB.0215 Periosteum & Endosteum SOM.MK.I.BPM1.1.FTM.3.HCB.0215 Non-calcified connective tissue layers covering external and internal surfaces of bone, except over articular surfaces Periosteum Attached to the outer circumferential lamellae by Sharpey’s fibers (type 1collagen) Composed of two layers: Outer fibrous layer consists mostly of a dense irregular connective tissue with fibroblasts. Contains blood vessels and nociceptors. Inner cellular/osteogenic layer layer contains osteoprogenitor cells BMP1 | MSK | Lecture 19 | Bone I and their derivatives (periosteal cells) Cells actively secreting matrix increase the width of bone (appositional growth)  SOM.MK.I.BPM1.1.FTM.3.HCB.0215 Periosteum and endosteum Inner cellular layer Outer fibrous layer Periosteum BMP1 | MSK | Lecture 19 | Bone I H/E  SOM.MK.I.BPM1.1.FTM.3.HCB.0216 Periosteum & Endosteum Endosteum Lines any space or cavity in bone (marrow spaces, haversian canals, Volkmann's canal) Contains mesenchymal stem cells which have the potential to differentiate into osteogenic progenitor cells and differentiated osteoblasts, fibroblasts, blood vessels, and sympathetic nerves BMP1 | MSK | Lecture 19 | Bone I Contains osteoclasts (bone remodeling occurs from within)  SOM.MK.I.BPM1.1.FTM.3.HCB.0216 Endosteum Section through developing (immature) bone. Marrow space BMP1 | MSK | Lecture 19 | Bone I Endosteum Trichrome med mag  SOM.MK.I.BPM1.1.FTM.3.HCB.0217 Bone Growth and Remodeling Elongation of bones is a result of interstitial growth of cartilage at epiphyseal growth plate Interstitial (internal) growth does not occur in bone Bone increases in width by appositional growth (osteoprogenitor cells in the periosteum) BMP1 | MSK | Lecture 19 | Bone I Remodeling of bone is a coordinated action between osteoblasts and osteoclasts  SOM.MK.I.BPM1.1.FTM.3.HCB.0217 Classification of Bone 1. Immature (primary or woven or bundle) bone First bone elaborated; contains numerous osteocytes and irregularly arranged collagen Low mineral content Remodeled and replaced by mature bone except in certain places such as in tooth sockets, near suture lines in the bones of the skull, and at insertion site of tendons BMP1 | MSK | Lecture 19 | Bone I  SOM.MK.I.BPM1.1.FTM.3.HCB.0217 Classification of Bone 2. Mature (secondary or lamellar) bone Replaces primary bone and made up of Haversian systems, or osteons Calcified matrix is arranged in regular concentric layers of lamellae (3 to 7 nm thick) surrounding a Haversian canal that transmits blood vessels, nerves and some loose connective tissue Osteocytes in lacunae are BMP1 | MSK | Lecture 19 | Bone I located between the lamellae and occasionally within them  SOM.MK.I.BPM1.1.FTM.3.HCB.0217 Immature vs Mature bone Immature bone Mature Immature Bone Mature Bone Immature Bone Gross Non-lamellar Lamellar, structure No haversian haversian systems systems Compact outside, spongy inside Collagen Random Parallel, stress fiber (disorganized) oriented arrangement (organized) Osteocyte High (many) Relatively low population (few) Mature Bone density Constitution Low mineral High mineral BMP1 | MSK | Lecture 19 | Bone I density: high density: low water content water content Location Embryo, newborn, Develops from 1- fracture callus, month post natal growth plate  SOM.MK.I.BPM1.1.FTM.3.HCB.0217 Types of Secondary (Mature) Bone 1. Compact Bone Very dense and heavy 2. Spongy (Cancellous) Bone Filled with spaces that are interconnected in long bone space filled with red (containing hemopoietic cells) or yellow (containing primarily fat) bone marrow BMP1 | MSK | Lecture 19 | Bone I  SOM.MK.I.BPM1.1.FTM.3.HCB.0218 Compact vs Spongy Bone Spongy bone Compact bone BMP1 | MSK | Lecture 19 | Bone I  SOM.MK.I.BPM1.1.FTM.3.HCB.0218 Compact Bone Functional unit = Haversian system or osteon Cylindrical and composed of 4 to 20 concentric lamellae Because bone is constantly being remodeled, the Haversian systems are NOT all uniform and in parallel array BMP1 | MSK | Lecture 19 | Bone I  SOM.MK.I.BPM1.1.FTM.3.HCB.0218 Compact Bone Have numerous canaliculi that permit communication between lacunae and with the Haversian canals Each lamella consists of multiple parallel arrays of collagen fibers. Adjacent lamellae, have alternating directions of collagen fibers providing great strength despite its BMP1 | MSK | Lecture 19 | Bone I light weight  SOM.MK.I.BPM1.1.FTM.3.HCB.0218 Compact Bone Outer & inner Circumferential Lamellae Deep to the periosteum the lamellae are arranged in concentric rings – Outer circumferential lamellae Similar arrangement of lamellae can be found next to the endosteum - Inner circumferential lamellae Interstitial lamellae are remnants of old remodeled osteons BMP1 | MSK | Lecture 19 | Bone I between newly laid down osteons  SOM.MK.I.BPM1.1.FTM.3.HCB.0223 Inner and Outer Circumferential Lamellae These follow the entire inner and outer circumferences of the shaft of long bones. OCL Both perforated by blood vessels and nerves as they access Volkmann's canals and Haversian canals BMP1 | MSK | Lecture 19 | Bone I OCL - lined by periosteum. ICL ICL - lined by endosteum  SOM.MK.I.BPM1.1.FTM.3.HCB.0218 Compact Bone SOM.MK.I.BPM1.1.FTM.3.HCB.0223 Volkmann’s canals Connect adjacent Haversian canals to each other and to endosteum of the marrow cavity on the inside and periosteum on the outside Allow for passage of neurovasculature through compact bone BMP1 | MSK | Lecture 19 | Bone I Fig.8.3  SOM.MK.I.BPM1.1.FTM.3.HCB.0223 Compact Bone BMP1 | MSK | Lecture 19 | Bone I 3D CT reconstruction of compact bone  SOM.MK.I.BPM1.1.FTM.3.HCB.0225 Label the indicated structures 1 6 Osteocyte lacunae 2 7 Endos 2 4 5 3 BMP1 | MSK | Lecture 19 | Bone I 8 Canaliculi 1. 2. 3. 4. 5. 6. 7. 8.