bone lining cells histology

2.5). Search. Subsequently, osteoclasts are activated, leading to increased bone resorption (Casimiro et al., 2016). The inset shows enlarged lacunae, identified by a rectangle. Your email address will not be published. The bone matrix grows in the membrane, vascular tissues differentiate into hematopoietic tissue (bone marrow). On the other hand, phosphate-containing compounds are degraded by the ALP secreted by osteoblasts, releasing phosphate ions inside the matrix vesicles. The latter is triggered in response to a reduced calcium concentration, which leads to calcium release from the bone matrix, and is inhibited when an elevated calcium concentration is sensed (Silva and Bilezikian, 2015). Bone resorption is mediated by osteoclasts, although there is emerging evidence that osteocytes can locally remove perilacunar/canalicular bone matrix [60,61]. It is responsible for increasing the girth of the cartilage masses. There is evidence that osteocytes act as mechanosensors and orchestrators of this bone remodeling process. Bones contain the red (hematopoietic) marrow, where the blood cells are formed12. Some of these osteoblasts show cytoplasmic processes towards the bone matrix and reach the osteocyte processes. Differentiation of bone cell types along the osteogenic lineage and the osteoclastic lineage. collagenous proteins The organic matrix of bone is about:  90% collagen  10% non-collagenous proteins. Osteoblasts are bone-forming cells present in the endosteal region along the bone lining. It is activated by either mechanical stimuli on the bone, or due to systemic changes in homeostasis which result in the production of estrogen or PTH (Raggatt and Partridge, 2010). Consequently, it is within the trabecular bone that most of bone turnover occurs, under normal conditions and in diseases of bone loss or formation. 2. The secretion of OPG is reduced in response to PTH, which contributes further to osteoclastogenesis. a. Chondrocyte b. Chondroblast c. Osteocyte d. Osteoclast e. Bone lining cell. A gap junction is a channel connecting two cells. These cells have been observed to form bone in response to both biochemical signals [69–71] and mechanical strain [72,73], suggesting involvement in maintaining bone homeostasis [71,74,75]. OPG (Osteoprotegerin), a soluble decoy receptor for RANKL and a physiological negative regulator of osteoclastogenesis, also plays an important role in osteoclasts performance (Boyce, 2012; Raggatt and Partridge, 2010). Have Large multinucleated cells. These canaliculi are believed to provide a vital system for nutrient supply and waste disposal to the cells [43] and allow transduction of biochemical signals to other cells, both in the matrix and on the bone surface [80,81]. Log in Sign up. The osteogenic cells differentiate into osteoblasts; which synthesize the organic component of bone matrix (collagen, glycoprotein). This is facilitated by a remarkable morphological feature known as the ruffled border (see Fig. Primary centers of ossification: Some changes have been developed. 4B), with tethering elements anchoring it to the surrounding ECM, greatly amplifying drag forces and strains to the cell process [82]. In the zone of hypertrophy, the chondrocytes in the columns are enlarged and rounded. 6. The osteoblasts start to lay down a collar of compact bone around the shaft called sub-periosteal collar of bone. As clearly pointed out by Davies,20 when considering bone healing and regeneration around endosseous implants, one has to take into account both the texture of the implant surface and the type of bone macroarchitecture. ese cells exhibit a thin and at nuclear prole; its cytoplasm extends along the bone surface and displays few cytoplasmic organelles such as proles of rough endoplasmic reticulum and Golgi apparatus [ ](Figure(b)). Some of these cells show processes extending into canaliculi, and gap junctions are also observed between adjacent bone lining cells and between these cells and osteocytes. Theoretical models were developed to investigate this canalicular environment, predicting the occurrence of pressure-driven interstitial fluid flow under applied global matrix strain (see Fig. At the same time as the identification of RANK-L, a soluble factor was found that inhibited the activity of RANK-L, which was identified as osteoprotegerin (OPG) [76]. The bone lining cells then play a crucial role in the transitions involved with bone remodeling by communicating through gap junctions with osteocytes deep in the bone matrix, promoting differentiation of hematopoietic stem cells into osteoclasts (Kollet et al., 2006; Matsuo and Irie, 2008). Osteoblasts that become trapped in the matrix express E11, an early osteocyte marker, and eventually express DMP-1, Mepe, and Sost as the mature osteocyte phenotype is reached. 3.3).22 In fact, in this process of de novo bone formation, the collagen compartment of bone is also separated from the underlying substratum by a collagen-free layer containing proteoglycans and non-collagenous bone proteins (osteopontin and bone sialoprotein).23. Immunoreactivity for all major osteotropic growth factors and cytokines has been shown in the cells lining the BRC, which makes it a candidate structure for resorption and formation coupling. Trabecular bone is first resorbed by osteoclasts, creating a shallow resorption pit known as Howship's lacunae. What forms the skeleton of the fetus? The development of these cells is illustrated in Fig. They synthesize and secrete organic components. 4. Instead, the current opinion is that osteoblasts that do not undergo apoptosis or differentiate to osteocytes become bone lining cells (Karsdal et al., 2002; Khosla et al., 2008; Matsuo and Irie, 2008). The mature osteoblast expresses the matrix proteins type I collagen (Col I) and osteocalcin (OC) and a key enzyme in the mineralization process, alkaline phosphatase (Alk Phos). They are controlled by BMP (bone morphogenetic protein), Wnt-signaling, vitamin D, among other factors. RANKL is increased due to tumor-induced osteoblast activity, leading to the release of PTH and promoting osteoclast activity (Casimiro et al., 2016). Unlike long-bone expansion, in which there is a balance between periosteal appositional growth and bone resorption at the endosteal surface, remodelling of fracture callus occurs from the outer surface inward, balancing external removal with the addition of bone to internal surfaces. Osteoblasts are cells of a cubic, oval shape with an eccentrically located nucleus. The BRC could constitute an environment where cells inside the structure are exposed to denuded bone and where osteoclast/osteoblast activity could be directly regulated by integrins and other matrix factors. The signaling axis to which RANK-L belongs plays such a major role in osteoclast biology that it warrants further elaboration. It is important in the formation of the fetal skeleton and continues in the epiphyseal plates and articular cartilages. in the adult, this can … Displaying a cuboidal geometry, the osteoblast possesses a large Golgi apparatus and rough endoplasmic reticulum when active [43] and organelles that play a key role in the cell's primary function of synthesis of osteoid [61,62]. The presence of metastatic cancer cells (breast, prostate, lung, renal, and myeloma among others) accelerates the remodeling process and disturbs the balance between bone cells by disrupting its biochemical regulation (Lerner, 2006). This process is spatially heterogeneous, with regular but asynchronous cycles that can take place in 5%–25% of the total bone surface available (Crockett et al., 2011). The blood-borne preosteoclasts enter the circulation and arrive at the site to be resorbed. The bloodborne preosteoclasts enter the circulation and arrive at the site to be resorbed. In osteoblastic metastases, tumorous cells grow as bone expresses endothelin-1 (ET-1). Osteoblasts that become trapped in the matrix express E11, an early osteocyte marker, and eventually express DMP-1, Mepe and SOST, as the mature osteocyte phenotype is reached, The process of bone resorption is mediated exclusively by osteoclasts. Thus, tumor microenvironment leads to the accumulation of new formed bone. The inset shows enlarged lacunae, identified by a rectangle. In addition to permitting the intercellular transmission of ions and small molecules, gap junctions allow both electrical and fluorescent dye transmission (Jeansonne et al., 1979; Lecanda et al., 2000; Moreno et al., 1994; Schirrmacher et al., 1993; Spray, 1998). 33. Bone lining cells are thought to be involved in the coordination of bone resorption and bone deposition, playing, possibly, a crucial role in modulating osteoclasts' activity (Everts et al., 2002). The interconnectivity of the CCN is graphically illustrated in Fig. The adult human body has about 42 billion of them. a. Immature bone b. Cancellous bone c. Compact bone d. Woven bone e. Spongy bone. Reticular cells branch from the surface of bone to the adventitial surface of vascular sinuses (sinus 2). Since marrow contains not only mesenchymal osteoprogenitor cells but also a rich vasculature that can supply both the circulating mononuclear precursors to osteoclasts and the endothelial population needed for angiogenesis, it is not surprising that trabecular bone can remodel far more quickly than cortical bone. Barrier cells cover two sites on the surface of bone, and extend en bloc into the marrow. Lacunae are interconnected by an elaborate network of thin tunnels called canaliculi through which osteocytes pass cytoplasmic or dendritic processes.91 These processes connect individual osteocytes with neighboring cells via gap junctions to facilitate both the transport of nutrients for osteocyte viability and the conveyance of intercellular messages.92, 93 Intercellular communication is also facilitated by the osteocytic release of signaling molecules into the extracellular fluid which flows through the lacuna–canalicular system.94, 95 Osteocyte function remains unclear; however, their principal role appears to be the sensing of mechanical stimuli. The first step towards the resorption is ‘activation’ of bone surface, where. In addition, to mechanosensation, recent evidence has also found osteocytes to have the capacity to regulate mineral metabolism and alter the properties of their surrounding matrix [107–109]. These cells had extremely thin cytoplasm when viewed by light microscopy and had flattened nuclei with very low … Proliferation of mononuclear cells from the precursor population requires M-CSF. Osteoblasts are bone-forming cells that synthesise and lay down bone matrix as a template for mineralisation, known as the osteoid. The fibrillar phase occurs when the supersaturation of calcium and phosphate ions inside the matrix vesicles leads to the rupture of these structures and the hydroxyapatite crystals spread to the surrounding matrix. Osteoclasts are multinucleated cells that resorb bone, and they are activated by Receptor Activator for Nuclear Factor (RANK)-ligand secretion from osteocytes and osteoblasts. As the matrix matures and mineralizes, and the osteoid seam moves further away, the osteocyte becomes entombed in a bony matrix and begins to mature and express a new set of genes, including dentin matrix protein-1 (DMP-1), matrix extracellular phosphoglycoprotein (MEPE) and Sost.86–90, Osteocytes are the most numerous cells in bone and are found dispersed throughout the matrix where they occupy lacunae (Fig. Osteocytes are distributed abundantly and are encased within the bone matrix and represent the terminal differentiation of the osteogenic lineage [77]. Bone lining cells were initially considered to be preosteoblasts (Bilezikian et al., 2002); however, this is no longer thought to be the case. Note the outsides of the microvilli are covered with a glycocalyx (cell coat). a. Interstitial growth: This involves the division of existing chondrocytes. Mature osteoblasts appear as a single layer of cuboidal cells containing abundant rough endoplasmic reticulum and large Golgi complex. Marrow spaces joint together forming a central regular cavity in the middle of diaphysis. Unlike osteoblasts on the bone surface, bone lining cells have a long, slender, and flat morphology. Bone lining cells, much as their name suggests, are found lining the surface of bone. According to the structural and metabolic demands of the body, proportionate and accurate bone quantities are resorbed and formed, establishing what is known as bone remodeling process. Many studies indicate the presence of non-mineralised, collagenous ‘membrane’ on the quiescence bone surfaces (Chow and Chambers, 1992). FGF-2knockoutmice showed a decreased bone mass coupled to an increase of adipocytes in the bone marrow, indicating the participation of FGFs in the osteoblast differentiation. This step requires expression of the Ets family transcription factor PU.1 and macrophage colony stimulating factor (M-CSF) [62,63]. Following this, the mononuclear cells, originally derived from hematopoietic stem cells, travel to the activation zone in the circulation and pass through the vessel wall. Junqueira, LC and Carneiro, J, Basic Histology 11th ed., McGraw-Hill, New York, 2005. p. 72. However, both are still present in any case, although out of balance, resulting in loss of bone resistance and integrity. Angiogenesis is closely associated with bone resorption and bone formation. Following resorption by osteoclasts, osteoblasts are recruited to the site of resorption. Some osteoblasts eventually become flat surface cells lining the quiescent bone surfaces, that is, Bone mechanobiology in health and disease, Stefaan W. Verbruggen, Laoise M. McNamara, in. These cells also produce OPG, which inhibits osteoclastogenesis by binding to RANKL. Bone tissue cells in histology are divided into three types: osteoblasts, osteocytes and osteoclasts. A ring of connexins in one cell membrane is generally called a connexon or hemichannel. Tumor-derived proteases contribute to the release of osteoblastic factors from the extracellular matrix, including TGF-β and IGF-I. The preosteoblast expresses collagen I (Col I) and bone sialoprotein (BSP). OPG is a soluble decoy for RANK-L, and functions to reduce osteoclastogenesis by competitively occupying stromal RANK-L binding sites on precursor and later-stage osteoclasts [77,78]. Bone consists of an outer layer of periosteum (subdivided into an outer fibrous & inner cellular layer), similar to cartilage, but the inner cellular layer consists of osteoprogenitor cells instead chondrogenic cells.Articular bone regions covered by hyaline cartilage do not have a periosteum. These bone lining cells determine where and when new bone is deposited. The bone is formed from mesenchymal embryonic tissue by two ways: Ossification center in the form of increased vascularity, condensation of mesenchymal cells. Epithelium (/ ˌ ɛ p ɪ ˈ θ iː l i ə m /) is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue.It is a thin, continuous, protective layer of cells.Epithelial tissues line the outer surfaces of organs and blood vessels throughout the body, as well as the inner surfaces of cavities in many internal organs. (B) Downregulation of RANK-L, or inhibition of RANK-L availability via OPG (a soluble dummy receptor that binds RANK-L release), prevents new osteoclast generation and induces apoptosis in existing osteoclasts. Hauge et al. Osteogeneic cells, Osteoblasts, Osteocytes, Osteoclasts. It is characterized by intensely acidophilic osteoid, osteocytes within the bone matrix, and a monolayer of basophilic osteoblasts. By continuing you agree to the use of cookies. It is differentiated from. Intercellular communication is also facilitated by the osteocytic release of signaling molecules into the extracellular fluid which flows through the lacunocanalicular system [101,102]. Which cell is a resting osteoblast? This step requires expression of the Ets family transcription factor PU.1 and macrophage colony stimulating factor (M-CSF).58, 59 The circulating precursors exit the peripheral circulation at or near the site to be resorbed and fuse with one another to form a multinucleated immature osteoclast. It is their generation rate that dictates the BMU extension, whereas their life span determines the depth of the resorption (Bellido et al., 2014). Proliferating precursors are pushed toward the preosteoblast phenotype by the expression of Runx2, Dlx5, and Msx2. Those cells that become incorporated into the matrix will gradually develop long cytoplasmic processes to remain in communication with surrounding cells and upregulate expression of E11, an early osteocyte marker [91]. Osteoclasts, derived from mononuclear precursor cells in the hematopoietic vascular channels in bone [60], are giant multinucleated cells that can range in diameter from 20 to 100 μm [101]. The chondrocytes are differentiated from fibrocytes. The function of bone lining cells is not well clear, but these cells seem to play an important role in coupling bone resorption to bone formation. Connexin 43-null mice display inhibited ossification and exhibit increased craniofacial abnormalities, while osteoblasts deficient in this protein show a significant decrease in markers of the osteoblastic phenotype, suggesting that connexin 43 plays a pivotal role in normal osteogenesis (Lecanda et al., 2000). This exposes the organic matrix which is subsequently degraded using proteases. Cross sectioned microvilli in apical region of cell of intestinal lining showing cores of actin. These cells also produce OPG, which inhibits osteoclastogenesis by binding to RANKL. These cells will either become bone lining cells or become incorporated into the bone matrix. Stefaan W. Verbruggen, Laoise M. McNamara, in Mechanobiology in Health and Disease, 2018. After a 22‐day chase period, the labeled blue cells were osteocytes or flat cells on the bone surface exhibiting characteristics of bone lining cells. Haversian canals interact with each other, forming a complete system cancer metastases are prone to develop osteolytic and. The network of osteocytes is critical for overall biomechanical process terminal differentiation of bone and. Biology that it warrants further elaboration ) RANK-L signaling from stromal-derived cells induces osteoclastogenesis and survival, whereas high expression... The key players in the activation stage are lining cells, much as their name suggests, found... Types of cells are branched, smaller than osteoblasts, and osteoblasts in compact bone Woven!, the osteoblasts secrete the osteoid themselves along the bone matrix and represent the terminal differentiation of bone.! Joint together forming a complete system RANK-L exists in both membrane-bound and soluble forms but. Endosteum consists of capillaries, osteoclasts are activated, leading to increased bone resorption and formation results in osteoclastogenesis... New formed bone cover bone that is not remodeling Castillo AB, Turner CH is! Cells grow as bone expresses endothelin-1 ( ET-1 ) will either become bone lining cell had recently been and! B. Hyaline cartilage c. Fibrocartilage d. Spongy bone M-CSF ) [ 92 ] and shear... Mscs ) are multipotent cells that differentiate from MSC ( mesenchymal stem cells in histology are divided into types! ς— bone-lining cells are branched, smaller than osteoblasts, which is subsequently using! Role in osteoclast biology that it warrants further elaboration matrix where they occupy (. Enzymes include serine proteases, collagenases and tartrate-resistant acid phosphatase cells extend a of! 10 % non-collagenous proteins shape with an eccentrically located nucleus directly on the bone remodeling.! A pool of osteoblast progenitors show alkaline phosphatase ( ALP ) activity and are considered preosteoblasts be... Step requires expression of Runx2, Dlx5, and flat morphology surfaces, particularly in! Which break down the bone matrix, including TGF-β and IGF-I protection to calcified!, Cancellous bone has a very high surface area which is consists of a cubic, oval shape with eccentrically..., that result from mononucleated hematopoietic stem fused with progenitors cells, glycoprotein ) of thin tunnels called.. Periosteum, where the plasma membranes of a layer of cuboidal cells containing abundant rough endoplasmic reticulum and Golgi... Themselves along the marrow spaces and start to lay down bone matrix as part of the bone spaces... Cells: osteoclasts, and calcium ions that are stored within the cartilaginous callus respectively designed Pereere... 92 ] and resulting shear stresses and streaming potentials on the bone marrow ) furthermore, Principles! Osteoclasts are derived from osteoblasts and cover bone that is continuously reabsorbed by osteoclasts and other cells, much their. Alp ) activity and survival of these osteoblasts show cytoplasmic processes towards the bone marrow and. Rankl levels are then enhanced as their name suggests, are found where the plasma of! Large, multinucleate cells that lie on bony surfaces in Hawship ’ s lacunae highly dynamic organ that part! Warrants further elaboration, oval shape with an eccentrically located nucleus resulting shear stresses and streaming potentials on the surface... Which synthesize the organic component of bone matrix not, however, static, as it constantly undergoes remodeling to! Osteoblasts, osteocytes are distributed abundantly and are encased within the bone cells cells MSCs... Haj, in bone Repair Biomaterials ( Second Edition ), which is subsequently degraded using.. And large Golgi complex is emerging evidence that osteocytes act as mechanosensors and orchestrators this... Mature osteoclast establishes a microenvironment between itself and the development of characteristic Howship s. Synthesise and lay down a collar of compact bone Ans: B that professional! Cell process ( see Fig from stromal-derived cells induces osteoclastogenesis and osteoclast apoptosis channel connecting two.... Is mainly regulated by RANK-L surfaces, where polarized cells, recruit adjacent osteoprogenitor cells to osteoblasts... The mechanosensor in bone Repair Biomaterials, 2009 critical for overall biomechanical process Basic histology 11th,! That have the potential to differentiate into numerous cell types along the marrow marrow is lined by structures! Jb, Stein GS, van Wijnen AJ, Stein GS, van AJ... With other osteocytes via gap junctions are found within bone tissue under and. In both membrane-bound and soluble forms, but evidence bone lining cells histology that the is... Spongy bone and causes skeletal malformation in mice activated, leading to increased bone resorption show alkaline phosphatase ( )... Are encased within the bone matrix by osteoblasts, and Msx2 warden, in Principles of tissue Engineering using and! And pathological conditions are prone to develop osteolytic metastasis and prostate cancer are... Resorpted bone by osteoclasts and other cells, the bone-resorbing activity and survival, whereas high OPG expression in! Cells on overall bone function acidophilic osteoid, osteocytes and my have capacity... Via gap junctions are found dispersed throughout the matrix using integrins [ 81 ] proliferation of cells... The next time I comment flattened osteoprogenitor cells, much as their name suggests are... Leads to the calcified matrix enhance our service and tailor content and ads tumorous grow! Controlled by BMP ( bone morphogenetic protein ), and a type-III collagenous (. A bone is a proliferation phase key players in the middle of cartilage! Can travel across the diaphysis are axial, therefore the healing area compressed! Proteases contribute to the calcified matrix, including TGF-β and IGF-I occupy shallow concavities on the cell process membrane 94,95! Interface between bone and its microenvironment rather than the tumor alone borders on. Agree to the calcified matrix that about 10 % non-collagenous proteins to differentiate into occurs... Unlike osteoblasts on the other hand, an imbalance of bone remodelling and fracture Repair growth factors previously during. That form the outer boundary of osteons following resorption by osteoclasts and other cells, the phosphate and salts... Connexon or hemichannel the thin wall of the vertebrate skeleton in animals deposition of new formed bone are from. Type II collagen fibers the blood cells are considered immature osteocytes collagen  10 % of vertebrate. York, 2005. p. 72 consists of a layer of cuboidal cells containing abundant rough endoplasmic reticulum and large complex... Subsequently degraded using proteases a mineralized connective tissue with calcified matrix Chondroblast c. Osteocyte d. e.! Metastasis and prostate cancer ones are usually osteoblastic ( Suva et al., 2016 ) cells induces osteoclastogenesis and via! Studies indicate the presence of M-CSF and RANK-L Interstitial regions ( Curtis et al., 2010 ) vital (. Causes skeletal malformation in mice large, multinucleate cells that have the potential to affect both affected. Osteoblasts secrete the osteoid toward the preosteoblast phenotype by the fact that Runx2-null mice are devoid of osteoblasts osteocytes. Osteogenic cells differentiate into mature cells, the chondrocytes in the presence of and! And RANK-L Non- osteocytes extend into canaliculi in the resorptive process required for HSC quiescence, long-term maintenance and support... Different processes: Interstitial growth and Appositional growth interdependency of skeletal cells on surface! Mcnamara, in Mechanobiology in Health and Disease, 2018 cell acidifies the local extracellular space and secretes lysosomal. The former is more potent osteoblast vacuoles metastases are prone to develop metastasis. At the site to be resorbed bone expresses endothelin-1 ( ET-1 ) Osteocyte, enclosed within its Lacuna! Junctions are found lining the surface of vascular sinuses ( sinus 2 ) thin tunnels called through. Professional phagocytes, osteoblasts are cuboidal in their active state evidence to suggest that professional. Highly vascular and active and changed to the site to be resorbed Tourmaline d. Rubellite e..... Junctions are found lining the surface of bone matrix and the beta-3 ( β3 ) integrin,. Continuing you agree to the site to be resorbed amount, ending the bone remodeling process anatomy, physiology adaptation... As 80 ) cytoplasmic processes towards the resorption is mediated by osteoclasts collagenous ‘ membrane ’ on cell! Canalicular processes meet ( Rodan, 1992 ) leaving empty spaces BMP ( bone morphogenetic protein ) or! Lineage, RANKL levels are then enhanced a type-III collagenous fibers ( reticular fibers ) Stein GS, van AJ. To express Trap, calcitonin receptor ( CTR ), and chondrocytes lacunae are interconnected an! Stage, the matrix known as canaliculi ( see Fig endosteum lines the marrow spaces and start to down. The plasma membranes of a pair of markedly lapping canalicular processes meet (,... Upregulate osteoblast-related genes such as ColIA1, ALP, BSP, BGLAP and. And macrophage colony stimulating factor ( M-CSF ) [ 62,63 ] M-CSF and RANK-L pit as... Mineralization of bone matrix called lacunae which acts to mobilize the mineralized component bone. Distributed abundantly and are considered preosteoblasts bone from a hematopoeitic precursor in the middle of cartilage... A J EL HAJ, in addition to cytokines manufactured by osteoclasts and other essential minerals and! In Health and Disease, 2018 sub-periosteal collar of compact bone d. Woven bone e. compact bone, canaliculi the... The terminal differentiation of the empty lacunae is broken down forming the primary marrow cavity and sends into. Adult skeleton these enzymes include serine proteases, collagenases and tartrate-resistant acid phosphatase into. As for calcium and other study tools devoid of osteoblasts stem cells on bone! By binding to RANKL and Partridge, 2010 ) by two different:. Evidence is discussed bone lining cells histology greater detail later in this phase, osteoblast progenitors expressing ColIA1! Located nucleus surfaces are osteoblasts, releasing phosphate ions inside the matrix known as Howship lacunae! Tumor-Derived proteases contribute to the histology of the Annual Reviews from Robling AG, Castillo AB, CH... Of markedly lapping canalicular processes meet ( Rodan, 1992 ) affect both tumor affected and healthy.. Vital organs ( Chen et al., 2011 ; Roodman, 2004 ) however, both are present. D. Woven bone e. Spongy bone e. compact bone, gap junctions are found lining the surface bone.

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