Bone and Bone Formation Flashcards
What does dense bone refer to?
Compact bone
What best describes the compact bone?
Characterized by presence of osteons
What best describes the Sharpey fibers?
Type I collagen of Sharpey fibers merges with the type I collagen in bone tissue
What is the main important mineral in bone?
Calcium Hydroxyapatite Crystals
What does a bone consist of?
Bone tissue, blood vessels, fat tissue, nerves, hyaline cartilage
What is the largest bone in the body?
Femur
What is the smallest bone in the body?
Stapes
What are the functions of a bone?
Produces red and white blood cells, provides attachment to muscles, support body upright against gravity, stores calcium and phosphate
What is calcium phosphate homeostasis in bone?
Calcium and phosphate can be mobilized from bone to blood to regulate levels in body
What other name is compact bone known by?
Cortical bone, Dense bone
What other name is spongy bone known by?
Trabecular bone, Cancellous bone
Spongy bone has sponge like meshwork known as?
Trabeculae
What does spongy bone hold in it?
Blood vessels and marrow
What is the epiphyseal plate?
Hyaline cartilage plate in the metaphysis at each end of long bone
What is the epiphyseal line?
Epiphyseal plate in adults that have stopped growing
Where is the metaphysis located?
Between the epiphysis and the diaphysis
What are bones covered by?
Periosteum
What does the periosteum consist of in actively growing bones?
Outer fibrous layer of dense connective tissue with vessels and nerves, and in inner cellular layer of osteoprogenitor cells
What does the periosteum consist of in adult bones?
Mostly outer fibrous layer of dense CT with vessels and nerves, and PERIOSTEAL CELLS
What are articular surfaces of bones in moveable joints covered with?
Hyaline cartilage
What is the inner cellular layer of periosteum known as?
Osteogenic Layer
T or F: There are more cells in the inner cellular layer in grown adults than growing bones?
False, less cells in adults inner cellular layer
What direction do collagen fibers of tendons and ligaments run?
Obliquely into the bone
What is the predominant type of collagen fibers in ligaments and tendons?
Type 1 Collagen
Collagen fibers of ligaments and bone merges with collagen fibers of ?
Extracellular bone matrix
What are Sharpey fibers?
Anchoring fibers, or perforating fibers, extending from the periosteum to the outer circumferential and interstitial lamellae
Do Sharpey fibers enter the bones osteon?
No
What is the inner aspect of the bone called?
Endosteum
What does the endosteum consist of?
Osteoprogenitor cells, and endosteal cells
What are osteoprogenitor cells?
Undifferentiated mesenchymal cells that can differentiate into osteoblasts
Where do hemopoiesis occur?
Red bone marrow
What does red bone marrow consist of?
Blood cells in different stages of development, network of reticular cells and fibers
What does red bone marrow get replaced with in adults?
Yellow bone marrow, fat cells
Where can red bone marrow be found?
Spaces of spongy bone in the sternum and iliac crest
Does hemopoiesis occur in yellow bone marrow?
No
Can yellow bone marrow convert back to red marrow when stimulated?
Yes, EX. extreme blood loss
What is another name for mature bone?
Lamellar bone
What is the lamellar bone composed of?
Osteons or Haversian systems, interstitial lamellae, circumferential lamellae
What is lamella?
Plates of type I collagen fibers cemented by calcium hydroxyapatite crystals
What does collagen plates arranged in RIGHT angles provide?
Maximum strength to the bone
What is another name for immature bone?
Non lamellar bone, Woven bone
Where is woven bone found?
Fetus, remodels to become mature bone
What is woven bone composed of?
Type I collagen bundles randomly arranged, randomly arranged cells, more ground substance than mature bone
Where can woven bone be found in adults?
Alveolar sockets
What is an osteon?
Concentric lamellae of bone matrix
What does an osteon surround?
Osteonal cannal or Haversian canal
What does an osteonal cannal contain?
Blood vessels, nerves, connective tissue
Osteonal canals are lined with?
Endosteum
What do osteonal canals contain?
Osteoprogenitor cells and endosteal cells
How are osteons arranged?
Long axis is parallel to long axis of bone
Collagen in the concentric lamellae are laid?
Parallel to one another
What gives maximum strength to osteons?
Different direction arrangement in between osteons and adjacent lamellae
The boundary of the osteon is demarcated by?
Cement line
Osteons contain?
Lacunae, slender canaliculi
Where are osteocytes located?
Lacunae
What do slender canaliculi contain?
Processes of osetocytes
What do slender canaliculi provide?
Communication between osteocytes, passage of substances between osteocytes and blood vessels
How are slender canaliculi arranged?
Radial to haversian canal
What is the Volkmanns canal?
Channels that allow blood vesselsand nerves to travel from the periosteum and endosteum to reach haversian canal
What does the Volkmanns canal connect?
Haversian canals together
Volkmanns canals are lined with?
Endosteal cells, not surrounded by concentric lamellae
What is another name for Volkmanns canals?
Perforating Canals
What is interstitial lamellae?
Remnants of previous concentric lamellae
What matrix does spongy bone have?
Lamellate matrix
Can spongy bone contain osteons?
Only in thick trabeculae
Where are osteoprogenitor cells derived from?
Mesenchymal stem cells in bone marrow
What can osteoprogenitor cells differentiate into?
Osteoblasts, chondroblasts
Why are osteoprogenitor cells important?
Important for bone repair and cartilage formation in fracture sites
Where are osteoprogenitor cells found?
Inner cellular layer of periosteum, endosteal lining of haversians and volkmanns canals
What do osteoprogenitor cells looks like?
Flattened squamous cells, ovoid nucleus, inconspicuous cytoplasm
What do osteoblasts secrete?
Unmineralized bone matrix, osteoid (Type I collagen and bone matrix proteins)
Bone matrix proteins:
Calcium binding proteins, multiadhesive glycoproteins, proteoglycans, alkaline phosphate
What do osteoblasts intiate?
Mineralization of bone matrix
Osteoblasts secrete small membrane bound matrix vesicles that contain?
Alkaline phosphate ALP
Osteoblasts are secreted only when
Matrix is produced
What do osteoblasts look like?
Cuboidal or polygonal, single layer of cells in apposition to newly forming bone
Osteocytes are mature bone cells and
Non dividing
What do osteocytes have radiating from body that extend into canaliculi?
Long cell processes
Where do osteocytes live?
Individual lacunae
How do osteocytes communicate with other cells?
Gap junctions
How do osteocytes communicate with osteoblasts, endothelial cells, and pericytes of blood vessels?
Signaling molecules, Ex. nitric oxide
What are the two types of bone lining cells?
Periosteal cells, endosteal cells
How do bone lining cells communicate with each other and osteocytes?
Gap junctions
Where are osteoclasts derived from?
Fusion of mononuclear hemopoietic cells (monocyte cell lineage)
Where are osteoclasts located?
Sites where bone is resorbed
What is resorption bay or Howships lacuna?
Shallow bays where osteoclasts rest directly on bone tissue, where resorption occurs
What activates osteoclasts?
Osteoblasts
What do actively resorbing osteoclasts show?
Ruffled border, clear zone or sealing zone, basolateral zone
What does the ruffled border contain?
Numerous plasma membrane foldings
What do the microvillous structures of the ruffled border provide?
Increased surface area for release of hydrolytic enzymes and exocytosis of degraded bone debris
Clear zone or sealing zone does what?
Demarcates the bone area for resorption
What does the clear zone or sealing zone have abundantly?
Actin filaments
How are actin filaments arranged in the clear zone?
Ring like structure surrounded by actin binding proteins
The plasma membrane of the osteoclasts forms a tight seal with?
Bone matrix
What does the basolateral region function in?
Exocytosis of digested material
Transport vesicles containing digested bone material fuse with cell membrane of the ______ to release contents
Basolateral region
Osteoporosis
The imbalance between bone resorption and bone formation by osteoblasts
What is osteoporosis exacerbated by?
Estrogen deficiency in postmenopausal women
Hormone replacement therapy is effective in what disorder?
Osteoporosis
Administration of calcitonin inhibits?
Bone resorption
What is osteopetrosis?
Hereditary bone disease
Failure of osteoclastic bone resorption leads to ?
Increased bone mass
Remodeling of woven bone to compact bone is defective why?
Leads to greater bone fragility
Intramembranous ossification is?
Mesenchymal tissue directly replaced by bone
What is intramembranous ossification known as?
Membrane bone
Examples of intramembranous ossification?
Bones of skull and face, mandible, flat portion of clavicle
Endochondral ossification is?
A cartilage model serves as the precursor of bone
Examples of endochondral ossification?
Long bones, vertebrae, pelvis
When does intramembranous ossification begin?
8th week of gestation in embryonic mesenchyme
Ossification center
Specific areas where mesenchymal cells migrate
Cells in ossification centers elongate and become
Osteoprogenitor cells
Osteoprogenitor cells differentiate into osteoblasts in presence of?
Transcription factor CBFA1
(core binding factor alpha 1)
Osteoblasts secrete
Type I collagen and matrix proteins: osteoid
T or F: Collagen fibers of osteoid form a woven network without a preferential orientation and lamellae are not present at this stage
True
Osteoid later calcifies and the osteoblasts get trapped in lacunae and become?
Osteocytes-called woven bone
In intramembranous ossification, osteocytes communicate with each other by
Cytoplasmic processes
Newly formed bone appears as irregularly shaped
Trabecular or spicules
Osteoblasts come into apposition with new bone and?
Add more bone matrix
Further growth and remodeling of intramembranous ossification results in
Replacement of woven bone by compact bone in the periphery, spongy bone in center, spaces in between trabeculae become occupied by bone marrow
When does endochondral ossification begin?
8th week of gestation
Proliferation and aggregation of ______ cells are at the site of future bone
Mesenchymal cells
Mesenchymal cells are under the influence of what during endochondral ossification?
Bone morphogenetic proteins (BMPs)
What do bone morphogenic proteins cause mesenchymal cells to do in endochondral ossification?
Differentiate into chondroblasts and express type II collagen
Chondroblasts lay down?
Hyaline cartilage model of future bone
How does hyaline cartilage model of future bone increase in length?
Interstitial growth
How does hyaline cartilage model of future bone increase in width?
Appositional growth
What happens after cartilage model of future bone is fully established?
Perichondrium stops producing chondrocytes and forms osteoblasts
Osteoblasts lay down a cuff of bone around the mid part of cartilage model known as:
Bony collar
Formation of bony collar is the FIRST sign of what?
Ossification
How is bony collar formed?
By intramembranous ossification
Once cartilage model is established, perichondrium is now called what?
Periosteum
With the establishment of periosteal bony collar, what happens to chondrocytes in mid region of cartilage?
They hypertrophy
What does hypertrophied chondrocytes cause?
Resorption of the cartilage matrix around large hypertrophied cells, leads to thin irregular cartilage plates between cells
Large hypertrophied cells secrete
Alkaline phosphates
What do alkaline phosphates do for large hypertrophied cells?
Leads to calcification of the bone matrix
Calcified cartilage matrix inhibits what?
Diffusion of nutrients
Diffusion of nutrients is inhibited in cartilage matrix and leads to
Death of chondrocytes in cartilage model
Chondrocyte death leads to
Matrix breakdown, neighboring lacunae become confluent to produce large cavities, blood vessels grow in cavities through the bony collar
Blood vessel growth into the cavity leads to migration of what two cell types into the cavity?
Periosteal mesenchymal cells that differentiate into osteoprogenitor cells, and Hemopoietic stem cells that give rise to blood cells
Osteoprogenitor cells make contact with calcified cartilage spicules and become?
Osteoblasts
Osteoblasts lay down osteoid on cartilage spicule framework of _____bone
Endochondral
What is the primary ossification center?
First site where bone begins to form in the diaphysis of a long bone
What is mixed spicule?
Combination of bone and underlying cartilage
What happens in a mixed spicule?
Calcified cartilage component gets removed and remaining bone component may continue to grow by appositional growth or undergo resorption
Where does ossification spread to from the primary ossification center?
Until entire mid part of cartilage model is replaced by bone, called the diaphysis
Cartilage remaining at each end of the bone in the cartilage model is known as
Proximal and distal epiphyseal cartilage
When and where does the secondary ossification center form?
After birth, Proximal epiphyseal plate
Why does secondary ossification center happen?
Due to hypertrophy, degeneration, and calcification of epiphyseal cartilage
(Leads to formation of bone trabeculae and marrow)
Where does cartilage from the original model remain?
At the end of the bone, known as articular cartilage
Epiphyseal growth plate or disc is located?
Between the epiphyseal and diaphyseal cavities, known as a transverse disc
Secondary ossification center in the DISTAL epiphyseal cartilage develops when?
At a later time
Growth in length of a long bone is dependent on?
Epiphyseal growth plate
When does the endochondral bone growth in long bones occur?
Begins 2nd trimester and continues into early adulthood
During growth at epiphyseal plate, the thickness of the growth plate remains?
Constant
During growth at epiphyseal plate, amount of new cartilage equals?
Amount of cartilage resorbed
During growth at epiphyseal plate, resorbed cartilage is replaced by?
Spongy bone
A growing epiphyseal plate shows 5 distinct zones of
Cellular arrangement
What are the 5 zones of cellular arrangement
Resting Zone, Proliferation Zone, Hypertrophic Zone, Calcification Zone, Resorption Zone
Resting Zone:
No cell proliferation or matrix production
Proliferation Zone:
Chondrocytes are larger than reserve zone chondrocytes, they divide and get organized into columns, and actively produce cartilage matrix
Hypertrophic Zone:
Greatly enlarged chondrocytes, have clear cytoplasm, continue to secrete cartilage matrix
Why do chondrocytes in hypertrophic zone have clear cytoplasms?
Due to glycogen accumulation
Cartilage matrix get pressed into bands between chondrocytes, in what zone?
Hypertrophic Zone
Calcification Zone:
Cartilage matrix is calcified, hypertrophic cells degenerate
Resorption Zone:
Osteoprogenitor cells differentiate into osteoblasts and lay down osteoid on calcified cartilage spicules, and mixed spicules are formed
Where is the resorption zone located?
Near diaphysis, calcified cartilage is in direct contact with connective tissue of marrow cavity
As bone is laid down on calcified spicules, cartilage is resorbed, leaving?
Spongy bone
Spongy bone is remodeled through?
Osteoclastic activity and new bone formation
When spongy bone is being formed, at the epiphyseal end the new cartilage matrix is formed to maintain _______ of epiphyseal plate
Thickness
What causes the actual lengthening of bone?
New cartilage matrix formation in epiphysis, pushes the epiphysis away from the diaphysis and elongates the bone
Growth in width or increase in diameter occurs by?
Appositional growth
What does appositional growth do to increase width of bone?
Periosteal cells differentiate into osteoblasts, osteoblasts form bony ridges, ridges enclose blood vessels, concentric lamellae of bone is laid down to form osteon
What happens when an individual reaches maximal growth?
Proliferation of the new cartilage in epiphyseal plate terminates, cartilage that has already been produced continues to deposit until none is left to deposit
Epiphyseal line in adults is ?
Site of epiphyseal cartilage, where epiphyseal and diaphyseal marrow cavities become confluent
A haversian canal with its encircling lamellae is known as?
Osteon
What is the function of canaliculi?
Passage of diffusion of nutrients to the osteocytes
