Learning Objectives

Observe and also describe the processes of bone remodeling and bone growth.Name the various histological areas of bone.Explain the procedure of bone turnover.Describe the calcification procedures of cartilage and also bone.Identify some vital pathological instances relevant come bone histology.

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bone osteoblastosteocyteosteoclastruffled borderHowship"s lacuna osteoidtype ns collagen glycosaminoglycan (GAG)calcium hydroxyapatitecompact bonecortical bonetrabecular bonecancellous bone spongy bonebone marrowepiphyses diaphysis epiphyseal expansion plate metaphysis articular cartilageperiosteumendosteumHaversian systemlamellaeHaversian canalVolkmann"s canallacunae canaliculiwoven bonelamellar boneendochondral ossification intramembranous ossification activation resorption reversal formation cement line
Mechanical assistance for sites of muscle attachmentProtection of an essential organsIon reserve of Ca and PO for metabolic functions

Bone Cells and Matrix

Bone is a tissue in i beg your pardon the extracellular matrix has actually been hardened come accommodate a sustaining function. The fundamental components that bone, prefer all connective tissues, room cells and matrix. There space three crucial cells the bone tissue. They every have unique functions and also are acquired from two different cell lines.
Osteoblasts synthesize the bone matrix and are responsible for its mineralization. Lock are acquired from osteoprogenitor cells, a mesenchymal stem cell line.Osteocytes space inactive osteoblasts that have come to be trapped in ~ the bone they have forcentregalilee.com.Osteoclasts break down bone matrix with phagocytosis. Predictably, they are acquired from the monocyte (macrophage) cabinet line. Think that osteoclasts as the "bone version" of the macrophage. Their task occurs follow me their ruffled border, and the an are between the osteoclast and the bone is well-known as Howship"s lacuna.
The balance between osteoblast and also osteoclast activity governs bone turnover and also ensures the bone is no overproduced nor overdegraded. These cells build up and break down bone matrix, which is written of:
Osteoid, i m sorry is the unmineralized matrix written of kind I collagen and also glycosaminoglycans (GAGs).Calcium hydroxyapatite, a calcium salt decision that provides bone its stamin andrigidity.
Bone is separated into two species that are various structurally and also functionally. Many bones of thebody consist of both types of bone tissue:
Compact bone, or cortical bone, greatly serves a mechanical function. This is the area of bone come which ligaments and tendons attach. It is thick and dense.Trabecular bone, additionally known as cancellous bone or spongy bone, largely serves a metabolic function. This type of bone is located in between layers that compact bone and is thin and also porous. Situated within the trabeculae is the bone marrow.

Macroscopic Bone Structure

The epiphyses are at the end of the lengthy bone and also are the components of the bone that participate in joint surfaces.The diaphysis is the pillar of the bone and also has walls of cortical bone and also an underlying network the trabecular bone.The epiphyseal expansion plate lies in ~ the interface in between the shaft and also the epiphysis and is the region in i m sorry cartilage proliferates to reason the elongation that the bone.The metaphysis is the area in i beg your pardon the column of the bone joins the epiphyseal expansion plate.
The epiphyses space lined through a class of articular cartilage, a specialized form that hyaline cartilage, i beg your pardon serves as protection versus friction in the joints.The outside of the diaphysis is inside wall by periosteum, a fibrous external layer ~ above which muscles, ligaments, and also tendons attach.The inside of the diaphysis, in ~ the border in between the cortical and also cancellous bone and lining the trabeculae, is lined by endosteum.

Microscopic Bone Structure

Compact bone is organized as parallel columns, known as Haversian systems, which operation lengthwise under the axis of long bones. These columns space composed of lamellae, concentric ring of bone, bordering a main channel, or Haversian canal, that contains the nerves, blood vessels, and lymphatic mechanism of the bone. The parallel Haversian canals are linked to one one more by the perpendicular Volkmann"s canals. The lamellae of the Haversian equipment are created by osteoblasts. As these cells secrete matrix, they become trapped in spaces dubbed lacunae and become known as osteocytes. Osteocytes connect with the Haversian canal through cytoplasmic expansions that run with canaliculi, tiny interconnecting canals. The class of a long bone, start at the outside surface, are therefore:
Periosteal surface of compact boneOuter circumferential lamellaeCompact bone (Haversian systems)Inner circumferential lamellaeEndosteal surface ar of compact boneTrabecular bone

Bone Development

Bone advancement begins with the replacement of collagenous mesenchymal organization by bone. This outcomes in the formation of woven bone, a primitive kind of bone through randomly organized collagen fibers the is more remodeled into mature lamellar bone, i m sorry possesses constant parallel ring of collagen. Lamellar bone is then constantly remodeled by osteoclasts and osteoblasts. There room two various methods by which bone is created from mesenchymal tissue:
Endochondral ossification is the process by which cartilage is progressively replaced by bone at the epiphyseal expansion plates. This occurs in long bones, the vertebrae, and the pelvis.Intramembranous ossification is the procedure by i beg your pardon mesenchymal organization is straight replaced by bone without an intercentregalilee.comiate cartilage step. The occurs most notably in the skeleton of the skull.

Bone Remodeling

In adults, after expansion has ceased, bone is forcentregalilee.com by the osteoblasts just where the was previously resorbed by the osteoclasts. This follows a certain sequence that events, and takes about three months in total to complete:
Activation - In the process of activation, osteoblasts induce osteoclasts to failure bone matrix. This wake up via the Receptor Activator because that NFkB-Ligand (RANK-L) signaling pathway, in i beg your pardon RANK-L on the surface of osteoblasts binds to rank on osteoclasts to revolve them on. This procedure lasts for roughly 3 days.Resorption - In resorption, the ruffled border the the osteoclast forms a sealing zone i m sorry isolates the area that bone erosion. Essential acids and lysosomal enzymes dissolve the mineral component and break down the organic matrix, respectively. This procedure occurs at approximately 14 days.Reversal - over time, osteoblasts begin to replace osteoclasts at the site of bone turnover.Formation - Osteoblasts begin to lay down new lamellar bone on optimal of old bone. In law so, cement currently are produced to note the borders in between old and brand-new bone matrix. This can take approximately 70 days come complete.
Answer: Haversian canals are central channels in bone the contain nerves, vessels, and lymphatics. They all operation parallel to every other yet are connected perpendicularly by Volkmann"s canals. Canaliculi are tiny expansions of the osteocytes with the bone matrix. They allow these isolated cell to interact with one another.
Name some bones that room forcentregalilee.com through endochondral ossification and some that space forcentregalilee.com v intramembranous ossification. What is the an essential difference between these two varieties of bone formation?
Answer: Endochondral ossification requires the conversion of cartilage come bone. This occurs in most long bones the the body. Intramembranous ossification does no involve a cartilage precursor. It takes ar in the skeletal of the skull.
Name and describe the key steps in the succession of bone remodeling.
Answer: Activation, resorption, reversal, formation. Check out pre-lab for more details.


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Macroscopic company of BoneLong BoneTrabecular BoneCompact BoneHaversian SystemOsteoblastsOsteoblast EMOsteoclastsOsteoclast EMBone RemodelingIntramembraneous OssificationEndochondrial OssificationChondrocyte growth Sequence
Observe this on slide at short magnification. The calcified bone is purple. The non-calcified aspects are light blue. Find locations of compact bone and trabecular bone.
This slide mirrors endochondral ossification, the process by which cartilage is calcified to form bone. Begin by distinguishing bone native the surrounding muscle tissue and from the cartilage epiphyses. Show the regions in i m sorry cartilage is gift concerted into bone. Identify the particular areas wherein chondrocytes are resting, proliferating, maturing, experience hypertrophy, and also calcifying.
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Name the precursor to this cell.

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Answer: This is an osteocyte, i beg your pardon is one osteoblast thathas come to be encased in bone. The embryonic precursor come both the theseis the osteoprogenitor cell, a mesenchymal stem cell.