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Flashcards in Bone Deck (59)

Is bone a type of connective tissue?

Yes, bone consists of cells, fibers and ground substance like other connective tissues


What is the osteoid?

The unmineralized organic matrix made of fibers and ground substance


What causes bone to become rigid?

The mineralization of the organic matrix by deposition of hydroxyapatite crystals


What are osteoblasts?

Osteoblasts are basophilic and cuboidal (if active, flattened if inactive) and produce the organic extracellular matrix


Where are osteoblasts found?

Surface of bone tissue


What are osteocytes?

Cells that are within bone lacunae to maintain bone matrix


Are osteocytes connected?

Yes. Osteocytes are connected by gap junctions on cell processes


What are osteoclasts?

Multinucleated macrophages that remove bone.

Osteoclasts are acidophilic with a ruffled border, located next to Howship's lacunae


Name an example of a syncytium



What % collagen fibers make up the osteoid?

90% collagen fibers, 10% ground substance


How much mineral does bone consist of?

65% mineral (hydroxyapatite)

Hydroxyapatite gradually deposits on and within the collagen lattice of osteoid


What is the endosteum

Loosely organized connective tissue that has 3 continuous regions and is located within the bone

Diaphyseal endosteum lines the walls of the marrow cavity

Trabecular endosteum covers the trabeculae of spongy bone

Osteonal endosteum goes in to blood vessel canals that are within the bone


What cells produce osteablasts?

Osteprogenitor cells


Where do osteopregenitor cells originate?

Endosteum and inner layer of periosteum


What is the periosteum?

Thick outer connective tissue layer on bone that consists of a fibrous outer layer and an inner cellular layer


What are Sharpey's fibers?

Collagen fibers that anchor the periosteum to the bone


What is the Haversian system?

The osteon, the basic unit of mature compact bone


What are osteons composed of?

Concentric lamellae or layers of mineralized bone matrix around a central canal that holds blood vessels and connective tissue


How are osteons arranged?

Along the long axis of the bone


Where are osteocytes found in the osteon?

Positioned between the lamellae of the osteons


What are canaliculi?

Tiny channels that connect lacunae


What are Volkmann's (perforating) canals?

Channels in bone that transmit blood vessels from the periosteum or endosteum in to the bone.

This provides a functional connection between the endosteum and the periosteum so there is connective tissue covering all surfaces


How are perforating canals arranged?

Perpendicular to the Haversian canals (osteons)


Describe spongy bone

Spongy bone is found in the heads of long bones and fills most irregular bones


Describe compact bone

Compact bone forms the outer shell of all bone and shafts in long bones


What is intramembranous ossification?

Formation of bone within the mesenchymal tissue without a cartilage model

Most flat bones of the skull develop this way


How does intramembranous ossification work?

Mesenchymal cells differentiate to osteoblasts, osteablasts secrete the osteoid and become trapped.

Bone spicules form and fuse in to solid bone


What is bone formation from the periosteum called?

Intraembranous ossification


What is a bone spicule?

A small structure such as a calcium carbonate process that supports the soft tissue of certain invertebrates


What is a trabecula?

A small bar or septal membrane in the framework of an organ

Any intersecting osseous bars that occur in cancellous bone


What is enchondral ossification?

Occurs in the majority of bones in the body and uses a mineralized hyaline cartilage matrix as a model


How does endochondral ossification work?

Mesenchyme in the limb bud condenses on the limb axis and differentiate in to chondroblasts to provide a cartilage model of the bone

Chondrocytes degenrate as the matrix mineralizes and the bone collar forms


When do osteoblasts begin bone formation?

After chondrification, blood vessels enter the calcified cartilage and bring osteoprogenitor cells

The osteoblasts invade the lacunae left by the atrophied chondrocytes and begin to secrete osteoid on the calcified cartilage


What is the primary center of ossification?

The interior diaphysis undergoes ossification and forms the bone collar
A large space in the center becomes the marrow cavity


What is the secondary center of ossification?

Generally one secondary center in each epiphysis (end). No bone collar forms however bone formation occurs in the same endochondral fashion as the primary center


What is the bone collar?

The bone collar forms from cells derived from the perichondrium/periosteum of the diaphysis.

Layers are added to the bone collar peripherally as its remodeled


Does the bone collar form by intramembranous or endochondral ossification?



What is the physis

Growth plate. Remnants of the cartilage model where chondrocytes still have the ability to divide. Chondrocyte proliferation is linear and results in growth of bone length


What is the leading edge?

Cells are hypertrophying, expanding and dividing


What is the trailing edge

Cells begin to become calcified and cartilage is replaced with bone


What are the 5 zones of the physis?

Resting zone (reserved chondrocytes)

Zone of proliferation (chondrocytes stack in columns)

Zone of hypertrophy
Zone of calcification
Zone of ossification (osteoid)


What type of collagen do hypertrophic chondrocytes produce?

Type II still, but also Type X for hemoatopoiesis


How long does it take to turn over the entire thickness of the growth plate?

48 hours


What is a limiting factor in growth rates?

How big hypertrophic chondrocytes become prior to ossification (bigger lacunae = faster growth)


Name 3 things that occur in the zone of ossification

Capillary buds grow in to tunnels left by dead chondrocytes

Osteoblasts differentiate from osteoprogenitor cells

Osteoid is deposited on the surfaces of the thin tunnel walls


How do you tell intramembranous from endochondral ossification?

The presence of the cartilage extracellular matrix


What cells are present in mature bone?

Osteocytes, osteoclasts, osteoblasts

Constant remodeling


How to tell between bone collar formation and physis growth

Growth at the physis is much more organized


How do bones grow in width?

Osteoblasts from the periosteum deposit bone lamellae on the outer surface of the bone

Osteoclasts remove bone from the inner surface of the endosteum to enlarge the marrow cavity

This leads to the bone and marrow cavity both increasing


Is an osteoblast the same as an osteocyte?

An osteocyte is an osteoblast that has been trapped in a lacunae

Osteocytes can signal but can't add bone


What is woven bone?

Characteristic of the embryonal skeleton

Collagen fibers of the matrix are irregularly arranged


What replaces woven bone?

Lamellar bone via remodeling


What is lamellar bone?

Layered bone. This is normal type bone of mammals. Lamellar bone can be either cancellous (parallel lamallae) or compact (concentric lamallae)


What dictates lamellar organization?

The repeating pattern of collagen fibroarchitecture


What is a cutting cone?

New osteons form in a tunnel behind a grop of osteoclasts called a "cutting cone"

A blood vessel surrounded by osteoprogenitor cells then grows in this tunnel


How are osteons formed?

Osteoblasts line the edges of the tunnel and deposit lamallae at the periphery of the tunnel made by the osteoclasts

Layers are always added to the osteon from the outside towards the central canal


How is spongy bone remodeled?

Spongy bone is always trabecular even after remodeling

This is accomplished by selective absorption and deposition of bone of the surface


What is interstitial bone?

After osteons are remodeled, the remnants are left between new osteons


What is circumferential lamallae?

Under the periosteum and edosteum, several layers of lamallae completely encircle the diaphysis