Bone Flashcards
What are the main functions of bone tissue?
Support body weight and protects internal organs
Provides leverage for body movements
Mineral storage site
Helps regulate blood calcium levels
What are general characteristics of bone tissue?
ECM (bone matrix) > cells
Fibers > Ground substance
Fibers are collagen I fibers
Ground substance is GAGs, proteoglycans, and multi-adhesive glycoproteins
What are the 5 main bone cells?
Osteoblasts - bone builders
Osteocytes - bone maintainers
Osteoclasts - bone dissolvers
Osteoprogenitor cells - bone stem cells
Bone lining cells - inactive osteoblasts that protect the endosteal surface
What covers the external and internal surface of bone tissue?
External - periosteum
Internal - endosteum, lines marrow cavity and neurovascular canal. Covers surfaces of spongy bone
What are 2 things that are associated with bone but are not bone?
Bone marrow - red marrow and yellow marrow are 2 types of specialized CT inside bones
Growth plates - bands of hyaline cartilage that are replaced with bone
What are the components of long bones?
Diaphysis (Shaft) - long cylindrical portion with marrow cavity
Epiphysis - end of long bone and has articular cartilage to cover articulating surfaces
Metaphysis - regions where diaphyses flares out and approaches epiphysis, location of growth plate in many bone
What is the function of the periosteum? What are its characteristics? Active vs. Inactive?
External CT surrounding bone
Covers and protects the outer surfaces of bones except articular surface and places where tendons insert into bone.
Active periosteum - if new bone forming directly underneath it
Inactive (mature) periosteum - if new bone is not actively being formed
What are the 2 layers of active periosteum in developing fetal bone?
Outer fibrous layer protects and supports underlying bone. Contains fibroblasts that make collagen I fibers. Vascularized and innervated.
Inner cellular (osteogenic) layer directly contact bone tissue and contains stems cells and osteoblasts. Osteoprogenitor cells differentiate into osteoblasts. Osteoblasts deposited onto bone surface and begin to make and secrete osteoid
What are the layers of inactive (mature) periosteum and bone?
Outer fibrous layer protects and supports underlying bone
Inner cellular layer - periosteal cells are inactive osteoprogenitor cells and can reactivate and differentiate into osteoblasts when needed
How is periosteum anchored into bone tissue? What is the function?
Sharpey’s fibers
Prevent periosteum from detaching or peeling off the bone
What does endosteum do and what are the cells?
Lines marrow cavities of long bones, lines neurovascular canals in compact bone, and covers of bony spicules and trabeculae of spongy bone.
Single row of osteoprogenitor cells and osteoblasts.
Bone lining cells = inactive osteoblasts
Endosteal cells = inactive osteoprogenitor cells
What is the difference between bone matrix and osteoid?
Bone matrix - ECM of mineralized bone tissue
Osteoid - unmineralized matrix (organic components only)
What fibers are present in bone matrix?
Main is collagen I fibers - impart some flexibility so tissue is not too brittle. Matrix is strongly acidophilic
Collagen V fibrils
What are the properties of the ground substance of the bone matrix?
GAGs and proteoglycans: hyaluronan, chondroitin sulfate, and keratan sulfate
Multi-adhesive glycoproteins - most help hold matrix and cells together, Some bind mineral crystals to collagen I fibers.
Growth factors and cytokines - bone morphogenic proteins induce mesenchymal cells and osteoprogenitor cells to differentiate into osteoblasts
What are the functions of the minerals in the bone matrix?
Make bone rigid - allows it to resist deformation from compression and other mechanical forces, support body weight, and enable movement (anchors/levers that muscles use to move)
Storage site for minerals
What is the main mineral in bone?
Hydroxyapatite crystals
What are osteoprogenitor cells? What are they called when inactive?
Stem cells that divide and differentiate into osteoblasts.
When inactive - periosteal cells (periosteum) or endosteal cells (endosteum)
What are the functions of osteoblasts?
Synthesize and secrete osteoid and initiate its mineralization - euchromatic nucleus and basophilic cytoplasm
Synthesize and secrete substance that facilitate bone mineralization.
What aids osteoblasts to synthesize and secrete substances that facilitate bone mineralization?
Alkaline phosphatase (ALP) - facilitates osteoid mineralization by cleaving phosphate groups from larger minerals
Osteocalcin - facilitates the alignment of hydroxyapatite crystals along surfaces of collagen I fibers to improve bone quality
Where are osteoblasts located?
Bone surfaces and then they becomes osteocytes
What are osteocytes and their function? Where are they located?
Most common cell and surrounded by matrix
Each osteocyte sits in a fluid filled chamber called a lacuna. Each lacuna connected to each other by small tunnels called canaliculi
Function is to monitor matrix surrounding their lacuna and do some minor maintenance of it. Has role in bone remodeling
What is the function of osteoclasts? What are their properties?
Break down bone matrix during bone repair and remodeling by dissolving its mineral and organic components.
Are very large, multinucleated cells and acidophilic cytoplasm.
Located on bone surfaces and sit in depression called Howship lacunae
Distinguish osteoblasts, osteocytes, and osteoclasts
Osteoblasts - on bone surface and secrete osteoid
Osteocytes - In lacuna and surrounded by mineralized bone matrix
Osteoclasts - On bone surfaces and dissolving old ECM
What do active osteoclasts do and what are their regions?
Osteoclasts break down matrix.
Resorption chamber are area directly below an active osteoclast where acid enzymes are breaking down bone matrix
4 regions - ruffled border, clear zone, vesicular zone, and basal zone
What is the ruffled border of the osteoclast? What does it do?
Region of cell closest to resorption chamber
Hydrolytic enzymes and protons are released across this part of the cell membrane into the resorption compartment below
Region where broken down matrix components are endocytosed
What is the clear zone of the osteoclast? What does it do?
Region of cell that forms a tight seal on the bone surface and all around edge of resorption chamber.
Forms a tight seal that isolates the corrosive contents of the resorption chamber from the rest of bone surface
What is the vesicular zone of an osteoclast?
Middle area of cell containing unreleased secretory vesicles heading to resorption compartment or towards capillaries
What is the basal zone of an osteoclast?
Furthest from resorption chamber and contains nuclei and most cytoplasmic organelles
How are inorganic components broken down by osteoclasts?
Release inactive acid hydrolases (acid phosphatase) into resorption chamber
Proton pumps send H into resorption chamber and low pH and activate the acid hydrolases
Minerals released pass into the cytoplas of osteoclasts and transported to capillaries
How are organic components broken down by osteoclasts?
Osteoclasts release acid hydrolases (MMPs) into the resorption comparment which break down the organic components of the newly-demineralized matrix
Released components are endocytosed by osteoclasts
Osteoclasts finish breaking down these molecules and transport them to capillaries
What is the difference between compact bone and spongy bone?
Compact bone - outer layer of solid bone tissue that remodels throughout life, has osteons
Spongy bone - inner layer of bone tissue, 3D network of thin, bony spicules
Spongy is always deep to layer of compact bone. All bones contain some amount of both
What are 3 ways to classify bone tissue?
- Gross Level Appearance
- Microscopic Organization
- How it develops
What are the differences between primary and secondary bone tissue?
Primary bone tissue is immature and woven, disorganized
Secondary bone tissue is mature and lamellar. In compact bone so very organized with layers of lamellae, osteons. Spongy bone has lamellae but not osteons
What are some characteristics of primary bone?
Forms during fetal development or during bone repair
Irregular bundles of collagen
Temporary tissue
Resorbed by osteoclasts
Replaced by secondary bone
Exception is bone lining tooth sockets remains immature through life
What are some characteristics of secondary bone?
Consists of parallel or concentric bone lamellae
Collagen fibers are parallel in lamella
Has more mineral content than primary bone
Stronger than primary bone
May exist as spongy or compact bone
Contains osteons (Haversian systems)
Describe the organization of osteon
Osteon is organized around central Haversian canal
Several thin, concentric layers (lamellae) of bone tissue around each Haversian canal
Osteocyte lacunae lie between adjacent lamellae
Canaliculi orientated towards other lacunae or to Haversian canal
What is in the Haversian canal?
Contains nerves and blood vessels that provide the nerve and blood supply for every osteocyte in that osteon
What are the lamellar systems in compact bone?
Osteons have concentric lamellae
Interstitial lamellae - lamellar fragments interspersed among osteons
Outer circumferential lamellae - extend around outer circumference of bone
Inner Circumferential lamellae - extend along inner margins of the bone marrow cavity
