Bone Flashcards
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
Osteoclast
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?
Intramembranous
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
