What Types Of Cells Remove Excess Bone Tissue After Fracture Repair

Bone

Basic are made of a combination of compact bone tissue for strength and spongy bone tissue for compression in response to stresses.

Learning Objectives

Distinguish between compact and spongy os tissues

Key Takeaways

Fundamental Points

Compact os is the hard external layer of all bones that protects, strengthens, and surrounds the medullary cavity filled with marrow.
Cylindrical structures, chosen osteons, are aligned along lines of the greatest stress to the bone in order to resist bending or fracturing.
Spongy or cancellous bone tissue consists of trabeculae that are arranged as rods or plates with cherry bone marrow in between.
Spongy bone is prominent in regions where the bone is less dense and at the ends of long bones where the bone has to be more than compressible due to stresses that go far from many directions.

Fundamental Terms

trabecula: a small-scale mineralized spicule that forms a network in spongy bone
epiphysis: the rounded terminate of any long bone
osteocyte: a mature os cell involved with the maintenance of bone
osteon: any of the central canals and surrounding bony layers constitute in compact bone

Bone Tissue

Bones are considered organs because they contain diverse types of tissue, such as claret, connective tissue, nerves, and bone tissue. Osteocytes, the living cells of bone tissue, form the mineral matrix of bones. In that location are ii types of bone tissue: compact and spongy.

Compact Bone Tissue

Meaty bone (or cortical bone), forming the hard external layer of all basic, surrounds the medullary cavity (innermost part or bone marrow). Information technology provides protection and strength to basic. Meaty bone tissue consists of units called osteons or Haversian systems. Osteons are cylindrical structures that incorporate a mineral matrix and living osteocytes continued past canaliculi which transport blood. They are aligned parallel to the long centrality of the bone. Each osteon consists of lamellae, layers of compact matrix that surround a central canal (the Haversian or osteonic canal), which contains the bone'south blood vessels and nerve fibers. Osteons in meaty os tissue are aligned in the aforementioned direction along lines of stress, helping the os resist bending or fracturing. Therefore, compact bone tissue is prominent in areas of bone at which stresses are applied in only a few directions.

Components of compact bone tissue: Compact bone tissue consists of osteons that are aligned parallel to the long axis of the bone and the Haversian canal that contains the bone'south blood vessels and nervus fibers. The inner layer of bones consists of spongy bone tissue. The small dark ovals in the osteon stand for the living osteocytes.

Spongy Bone Tissue

Meaty bone tissue forms the outer layer of all basic while spongy or cancellous bone forms the inner layer of all bones. Spongy bone tissue does not comprise osteons. Instead, it consists of trabeculae, which are lamellae that are arranged every bit rods or plates. Red os marrow is found betwixt the trabuculae. Claret vessels within this tissue deliver nutrients to osteocytes and remove waste. The reddish bone marrow of the femur and the interior of other big basic, such every bit the ileum, forms blood cells.

Arrangement of trabeculae in spongy bone: Trabeculae in spongy bone are arranged such that one side of the bone bears tension and the other withstands compression.

Spongy os reduces the density of os, assuasive the ends of long basic to compress as the result of stresses applied to the bone. Spongy bone is prominent in areas of bones that are non heavily stressed or where stresses make it from many directions. The epiphysis of a bone, such as the neck of the femur, is subject to stress from many directions. Imagine laying a heavy-framed motion picture flat on the floor. You could hold up one side of the movie with a toothpick if the toothpick were perpendicular to the floor and the picture. Now, drill a pigsty and stick the toothpick into the wall to hang up the flick. In this example, the function of the toothpick is to transmit the downward force per unit area of the flick to the wall. The strength on the motion-picture show is straight down to the floor, but the force on the toothpick is both the picture wire pulling down and the bottom of the pigsty in the wall pushing up. The toothpick will break off right at the wall.

The neck of the femur is horizontal like the toothpick in the wall. The weight of the trunk pushes information technology downward about the joint, but the vertical diaphysis of the femur pushes it upward at the other end. The neck of the femur must exist strong enough to transfer the downward strength of the body weight horizontally to the vertical shaft of the femur.

Cell Types in Basic

The osteoblast, osteoclast, osteocyte, and osteoprogenitor bone cells are responsible for the growing, shaping, and maintenance of bones.

Learning Objectives

Distinguish among the iv cell types in bone

Fundamental Takeaways

Fundamental Points

Osteogenic cells are the only bone cells that divide.
Osteogenic cells differentiate and develop into osteoblasts which, in turn, are responsible for forming new bones.
Osteoblasts synthesize and secrete a collagen matrix and calcium salts.
When the expanse surrounding an osteoblast calcifies, the osteoblast becomes trapped and transforms into an osteocyte, the almost common and mature blazon of os jail cell.
Osteoclasts, the cells that intermission down and reabsorb bone, stalk from monocytes and macrophages rather than osteogenic cells..
There is a continual balance between osteoblasts generating new bone and osteoclasts breaking downwards bone.

Key Terms

osteoclast: a big multinuclear cell associated with the resorption of bone
osteocyte: a mature os cell involved with the maintenance of os
osteoprogenitor: a stem prison cell that is the forerunner of an osteoblast
canaliculus: any of many small canals or ducts in bone or in some plants
periosteum: a membrane surrounding a bone
endosteum: a membranous vascular layer of cells which line the medullary cavity of a bone
lacuna: a pocket-size opening; a small pit or depression; a small blank space; a gap or vacancy; a hiatus
osteoblast: a mononucleate cell from which bone develops

Jail cell Types in Basic

Bone consists of four types of cells: osteoblasts, osteoclasts, osteocytes, and osteoprogenitor (or osteogenic) cells. Each prison cell type has a unique office and is institute in different locations in basic. The osteoblast, the os cell responsible for forming new os, is found in the growing portions of bone, including the periosteum and endosteum. Osteoblasts, which practise non divide, synthesize and secrete the collagen matrix and calcium salts. Equally the secreted matrix surrounding the osteoblast calcifies, the osteoblast becomes trapped inside it. As a issue, information technology changes in construction, becoming an osteocyte, the primary prison cell of mature os and the nigh common type of os jail cell. Each osteocyte is located in a space (lacuna) surrounded by bone tissue. Osteocytes maintain the mineral concentration of the matrix via the secretion of enzymes. Every bit is the case with osteoblasts, osteocytes lack mitotic activity. They are able to communicate with each other and receive nutrients via long cytoplasmic processes that extend through canaliculi (singular = canaliculus), channels within the os matrix.

Bone prison cell types: Tabular array listing the office and location of the iv types of bone cells.

Four types of bone cells: 4 types of cells are constitute within bone tissue. Osteogenic cells are undifferentiated and develop into osteoblasts. When osteoblasts become trapped within the calcified matrix, their structure and office changes; they become osteocytes. Osteoclasts develop from monocytes and macrophages and differ in advent from other bone cells.

If osteoblasts and osteocytes are incapable of mitosis, and so how are they replenished when old ones die? The answer lies in the properties of a third category of os cells: the osteogenic prison cell. These osteogenic cells are undifferentiated with loftier mitotic activity; they are the only bone cells that divide. Immature osteogenic cells are plant in the deep layers of the periosteum and the marrow. When they differentiate, they develop into osteoblasts. The dynamic nature of os means that new tissue is constantly formed, while old, injured, or unnecessary os is dissolved for repair or for calcium release. The prison cell responsible for os resorption, or breakdown, is the osteoclast, which is found on bone surfaces, is multinucleated, and originates from monocytes and macrophages (two types of white claret cells) rather than from osteogenic cells. Osteoclasts continually break downwardly old bone while osteoblasts continually form new bone. The ongoing residue between osteoblasts and osteoclasts is responsible for the constant, but subtle, reshaping of bone.

Bone Development

Intramembranous ossification stems from fibrous membranes in flat bones, while endochondral ossification stems from long bone cartilage.

Learning Objectives

Distinguish between intramembranous and endochondral ossification

Cardinal Takeaways

Key Points

The ossification of the flat bones of the skull, the mandible, and the clavicles begins with mesenchymal cells, which then differentiate into calcium-secreting and bone matrix-secreting osteoblasts.
Osteoids course spongy bone around claret vessels, which is afterwards remodeled into a thin layer of compact bone.
During enchondral ossification, the cartilage template in long bones is calcified; dying chondrocytes provide space for the evolution of spongy bone and the bone marrow cavity in the interior of the long bones.
The periosteum, an irregular connective tissue around basic, aids in the attachment of tissues, tendons, and ligaments to the bone.
Until adolescence, lengthwise long bone growth occurs in secondary ossification centers at the epiphyseal plates (growth plates) near the ends of the basic.

Key Terms

osteoid: an organic matrix of protein and polysaccharides, secreted by osteoblasts, that becomes os after mineralization
endochondral: inside cartilage
chondrocyte: a cell that makes up the tissue of cartilage
diaphysis: the primal shaft of whatever long bone

Evolution of Bone

Ossification, or osteogenesis, is the procedure of bone formation by osteoblasts. Ossification is singled-out from the process of calcification; whereas calcification takes place during the ossification of bones, it tin can too occur in other tissues. Ossification begins approximately six weeks afterwards fertilization in an embryo. Earlier this time, the embryonic skeleton consists entirely of fibrous membranes and hyaline cartilage. The development of bone from gristly membranes is called intramembranous ossification; development from hyaline cartilage is called endochondral ossification. Bone growth continues until approximately age 25. Bones tin grow in thickness throughout life, but after age 25, ossification functions primarily in bone remodeling and repair.

Intramembranous Ossification

Intramembranous ossification is the process of bone development from gristly membranes. It is involved in the formation of the flat bones of the skull, the mandible, and the clavicles. Ossification begins as mesenchymal cells grade a template of the future bone. They then differentiate into osteoblasts at the ossification center. Osteoblasts secrete the extracellular matrix and deposit calcium, which hardens the matrix. The non-mineralized portion of the bone or osteoid continues to form around blood vessels, forming spongy bone. Connective tissue in the matrix differentiates into carmine bone marrow in the fetus. The spongy bone is remodeled into a thin layer of compact bone on the surface of the spongy os.

Endochondral Ossification

Endochondral ossification is the procedure of bone development from hyaline cartilage. All of the bones of the body, except for the flat bones of the skull, mandible, and clavicles, are formed through endochondral ossification.

Procedure of endochondral ossification: Endochondral ossification is the process of os development from hyaline cartilage. The periosteum is the connective tissue on the exterior of bone that acts every bit the interface between bone, claret vessels, tendons, and ligaments.

In long bones, chondrocytes form a template of the hyaline cartilage diaphysis. Responding to complex developmental signals, the matrix begins to calcify. This calcification prevents diffusion of nutrients into the matrix, resulting in chondrocytes dying and the opening up of cavities in the diaphysis cartilage. Blood vessels invade the cavities, while osteoblasts and osteoclasts modify the calcified cartilage matrix into spongy bone. Osteoclasts then break downward some of the spongy bone to create a marrow, or medullary cavity, in the center of the diaphysis. Dense, irregular connective tissue forms a sheath (periosteum) effectually the basic. The periosteum assists in attaching the os to surrounding tissues, tendons, and ligaments. The bone continues to abound and elongate as the cartilage cells at the epiphyses divide.

In the terminal stage of prenatal bone development, the centers of the epiphyses brainstorm to calcify. Secondary ossification centers grade in the epiphyses every bit claret vessels and osteoblasts enter these areas and convert hyaline cartilage into spongy bone. Until boyhood, hyaline cartilage persists at the epiphyseal plate (growth plate), which is the region between the diaphysis and epiphysis that is responsible for the lengthwise growth of long bones.

Growth of Bone

Long basic lengthen at the epiphyseal plate with the addition of bone tissue and increase in width past a process chosen appositional growth.

Learning Objectives

Describe the processes of postal service-fetal bone growth and bone thickening

Key Takeaways

Key Points

The epiphyseal plate, the surface area of growth composed of four zones, is where cartilage is formed on the epiphyseal side while cartilage is ossified on the diaphyseal side, thereby lengthening the bone.
Each of the four zones has a role in the proliferation, maturation, and calcification of bone cells that are added to the diaphysis.
The longitudinal growth of long basic continues until early adulthood at which time the chondrocytes in the epiphyseal plate stop proliferating and the epiphyseal plate transforms into the epiphyseal line as bone replaces the cartilage.
Bones tin increment in bore even subsequently longitudinal growth has stopped.
Appositional growth is the procedure by which former bone that lines the medullary crenel is reabsorbed and new os tissue is grown beneath the periosteum, increasing bone diameter.

Key Terms

metaphysis: the role of a long bone that grows during development
periosteum: a membrane surrounding a bone
ossification: the normal process by which bone is formed
chondrocyte: a cell that makes up the tissue of cartilage
hypertrophy: to increase in size
diaphysis: the central shaft of whatsoever long os
epiphysis: the rounded stop of whatsoever long bone
medullary: pertaining to, consisting of, or resembling, marrow or medulla

Growth of Os

Long bones keep to lengthen (potentially throughout boyhood) through the addition of bone tissue at the epiphyseal plate. They also increase in width through appositional growth.

Lengthening of Long Bones

The epiphyseal plate is the area of growth in a long bone. It is a layer of hyaline cartilage where ossification occurs in young bones. On the epiphyseal side of the epiphyseal plate, cartilage is formed. On the diaphyseal side, cartilage is ossified, allowing the diaphysis to grow in length. The metaphysis is the wide portion of a long bone between the epiphysis and the narrow diaphysis. It is considered a part of the growth plate: the part of the bone that grows during childhood, which, as it grows, ossifies near the diaphysis and the epiphyses.

The epiphyseal plate is composed of four zones of cells and activity.

The reserve zone, the region closest to the epiphyseal terminate of the plate, contains small chondrocytes within the matrix. These chondrocytes do not participate in os growth; instead, they secure the epiphyseal plate to the osseous tissue of the epiphysis.
The proliferative zone, the next layer toward the diaphysis, contains stacks of slightly-larger chondrocytes. It continually makes new chondrocytes via mitosis.
The zone of maturation and hypertrophy contains chondrocytes that are older and larger than those in the proliferative zone. The more than mature cells are situated closer to the diaphyseal end of the plate. In this zone, lipids, glycogen, and alkaline phosphatase accumulate, causing the cartilaginous matrix to lapidify. The longitudinal growth of bone is a result of cellular division in the proliferative zone along with the maturation of cells in the zone of maturation and hypertrophy.
The zone of calcified matrix, the zone closest to the diaphysis, contains chondrocytes that are dead because the matrix around them has calcified. Capillaries and osteoblasts from the diaphysis penetrate this zone. The osteoblasts secrete bone tissue on the remaining calcified cartilage. Thus, the zone of calcified matrix connects the epiphyseal plate to the diaphysis. A bone grows in length when osseous tissue is added to the diaphysis.

After the zone of calcified matrix, there is the zone of ossification, which is actually part of the metaphysis. Arteries from the metaphysis branch through the newly-formed trabeculae in this zone. The newly-deposited os tissue at the top of the zone of ossification is called the principal spongiosa. The older bone at the bottom of the zone of ossification is chosen the secondary spongiosa.

Longitudinal bone growth: The epiphyseal plate is responsible for longitudinal bone growth. This illustration shows the zones bordering the epiphyseal plate of the epiphysis. The topmost layer of the epiphysis is the reserve zone. The 2d zone, the proliferative zone, is where chondrocytes are continually undergoing mitosis. The next zone is the zone of maturation and hypertrophy where lipids, glycogen, and alkaline phosphatase accumulate, causing the cartilaginous matrix to calcify. The following zone is the calcified matrix where the chondrocytes take hardened and dice equally the matrix around them has calcified. The bottom-most row is the zone of ossification which is function of the metaphysis. The newly-deposited os tissue at the top of the zone of ossification is called the primary spongiosa, while the older os is labeled the secondary spongiosa.

Bones continue to grow in length until early adulthood with the rate of growth controlled by hormones. When the chondrocytes in the epiphyseal plate cease their proliferation and bone replaces the cartilage, longitudinal growth stops. All that remains of the epiphyseal plate is the epiphyseal line.

From epiphyseal plate to epiphyseal line: As a bone matures, the epiphyseal plate progresses to an epiphyseal line. (a) Epiphyseal plates are visible in a growing bone. (b) Epiphyseal lines are the remnants of epiphyseal plates in a mature bone.

Thickening of Long Bones

While bones are increasing in length, they are as well increasing in diameter; growth in diameter can continue fifty-fifty later on longitudinal growth ceases. This is called appositional growth. Osteoclasts, cells that piece of work to break down bone, resorb old bone that lines the medullary cavity. At the same time, osteoblasts via intramembranous ossification, produce new bone tissue beneath the periosteum. The erosion of sometime os along the medullary crenel and the deposition of new bone below the periosteum non only increase the diameter of the diaphysis, but also increment the bore of the medullary cavity. This process is called modeling.

Os Remodeling and Repair

Bone is remodeled through the continual replacement of old bone tissue, equally well as repaired when fractured.

Learning Objectives

Outline the process of bone remodeling and repair

Fundamental Takeaways

Primal Points

Bone replacement involves the osteoclasts which break downward os and the osteoblasts which brand new bone.
Bone turnover rates differ depending on the bone and the expanse within the bone.
There are four stages in the repair of a broken bone: i) the formation of hematoma at the break, 2) the formation of a fibrocartilaginous callus, 3) the formation of a bony callus, and 4) remodeling and addition of compact bone.
Proper bone growth and maintenance requires many vitamins (D, C, and A), minerals (calcium, phosphorous, and magnesium), and hormones ( parathyroid hormone, growth hormone, and calcitonin ).

Central Terms

callus: the material of repair in fractures of bone which is at showtime soft or cartilaginous in consistency, just is ultimately converted into true bone and unites the fragments into a single piece
spicule: a sharp, needle-like slice
fibroblast: a prison cell found in connective tissue that produces fibers, such as collagen

Bone Remodeling and Repair

Bone renewal continues after nativity into machismo. Bone remodeling is the replacement of sometime bone tissue by new bone tissue. Information technology involves the processes of bone degradation or bone production done by osteoblasts and bone resorption done by osteoclasts, which interruption down one-time bone. Normal bone growth requires vitamins D, C, and A, plus minerals such as calcium, phosphorous, and magnesium. Hormones such every bit parathyroid hormone, growth hormone, and calcitonin are also required for proper bone growth and maintenance.

Bone turnover rates, the rates at which old os is replaced by new os, are quite high, with 5 to seven pct of bone mass existence recycled every week. Differences in turnover rates exist in unlike areas of the skeleton and in different areas of a bone. For example, the bone in the head of the femur may be fully replaced every half dozen months, whereas the bone along the shaft is altered much more slowly.

Bone remodeling allows bones to adapt to stresses by becoming thicker and stronger when subjected to stress. Basic that are not subject to normal everyday stress (for example, when a limb is in a cast) will begin to lose mass.

Stages of fracture repair: The healing of a bone fracture follows a serial of progressive steps: (a) A fracture hematoma forms. (b) Internal and external calli grade. (c) Cartilage of the calli is replaced by trabecular os. (d) Remodeling occurs.

A fractured or broken bone undergoes repair through four stages:

Hematoma formation: Blood vessels in the broken os tear and hemorrhage, resulting in the germination of clotted claret, or a hematoma, at the site of the break. The severed blood vessels at the cleaved ends of the bone are sealed by the clotting process. Bone cells deprived of nutrients brainstorm to die.
Bone generation: Within days of the fracture, capillaries grow into the hematoma, while phagocytic cells begin to clear abroad the dead cells. Though fragments of the claret clot may remain, fibroblasts and osteoblasts enter the area and begin to reform bone. Fibroblasts produce collagen fibers that connect the broken bone ends, while osteoblasts outset to class spongy os. The repair tissue between the broken bone ends, the fibrocartilaginous callus, is composed of both hyaline and fibrocartilage. Some bone spicules may besides appear at this point.
Bony callous germination: The fibrocartilaginous callus is converted into a bony callus of spongy bone. It takes virtually two months for the broken bone ends to be firmly joined together subsequently the fracture. This is similar to the endochondral formation of bone when cartilage becomes ossified; osteoblasts, osteoclasts, and os matrix are present.
Bone remodeling: The bony callus is then remodelled by osteoclasts and osteoblasts, with excess cloth on the exterior of the bone and inside the medullary cavity being removed. Compact bone is added to create os tissue that is similar to the original, unbroken os. This remodeling can take many months; the os may remain uneven for years.