Exam 2 - MSK 1A Bone: Normal Structure Flashcards
2 types of bone?
- Cortical Bone
2. Cancellous Bone
Percent of Cortical Bone? Turn over rate? Density and packed with what?
80% of bone. Slow turn over. Dense and packed with haversian canal system.
Haversion System aka?
Osteon
What and where is the Haversian Canal? In which type of bone? Communicates with what?
Central canal of Cortical Bone. Contains blood vessels and nerves that communicate with periosteum.
Lamelle are found where, what shape, and in what type of bone?
Concentric layers of bone surrounding Central/Haversian Canal. In Cortical Bone.
Osteocytes are found where and active in what functions?
Within Lamelle (concentric layers around Central/Haversian Canal) on Cortical Bone. Active in signaling, maintenance, and turn-over.
What is Volkman’s Canal and in which type of canal? What does it connect to?
Horizontal canal in cortical bone. Connects to periosteum.
Cancellous Bone described as ____ or ____
Trabecular or spongy bone
What % is Cancellous bone? Density? Turnover rate?
20% of bone. Less dense than cortical bone but large surface area. High turnover rate.
Cancellous Bone undergoes remodeling along what/where?
Along lines of stress
What is Wolff’s Law?
Increased mechanical stress will increase bone density
Describe the Periosteum. Where is it?
Thin, double-layered, tough fibrous membrane. Layer that surrounds bone.
Where does Periosteum cover and not cover? (Hint: 2 places)
Covers all bone EXCEPT at ligament or tendon insertion sites.
Periosteum does not cover at which two places?
- Ligament insertion sites
2. Tendon insertion sites
Outer layer of Periosteum contains what two things?
- Capillaries
2. Nerves
What fiber does Inner Layer of Periosteum contain? What does it do? Includes what two things?
Sharpey’s Fibers. Anchors Periosteum to Cortical Bone. Includes tendons and ligaments.
What contained if inner layer of Periosteum is active? Inactive?
Active=Osteoblasts
Inactive=Fibroblasts (can become osteoblasts)
Where and what are fibroblasts?
Within inactive inner layer of periosteum. Can become osteoblasts if new growth needed.
Bone Marrow aka? Where confined to?
Myeloid Tissue. Confined to cavities between osseus component of bone.
General function and regions/types of bone marrow?
Function=Form new blood cells
- Red (active)
- Yellow (Inactive)
Where is Red Bone Marrow? Do all bone have it?
Found in trabecular or spongy bone regions (cancellous bone). Not all bones have it. Found in: Pelvis, vertebra, cranium, manubrum, sternum, ribs, and humerus
Where is Yellow Bone Marrow? What does it represent?
Found in medullary cavity of long bone. Inactive. Represents fatty cells.
What is the name of the artery which supplies the primary source of blood to bones? Where on the bone do they enter?
Nutrient arteries. Enter in middle of diaphysis.
What can a fracture cause a bone to become? Which bones are most likely or “precious”?
Necrotic.
Prox humerus, prox femus, scaphoid, talus, and base of 5th metatarsal are “precious” bones which can become necrotic from a fx
What are the two main components of blood?
- Cellular component
2. Extra Cellular Matrix component
What are the three “osteos” of the Cellular Component of bone?
- Osteoblasts
- Osteoclases
- Osteocytes
What long list of things makes up the Extra Cellular Matrix component of bone?
Collagen, ECM proteins, proteoglycans, cytokines, growth factors, minerals, etc
Osteoprogenitor cells make what?
Osteoblasts
Osteoblasts comes from which cells? Where are Osteoblasts located?
From osteoprogenitor cells. Located on bone surfaces and inner surface of periosteum.
Osteoblasts located on bone surfaces (Haversian Canal, trabecular) and innersurface of periosteum are what?
Metabolically active
Osteoblasts located in deeper bone are what? How can that change?
Metabolically inactive until stimulated by physical disruption (Trauma, fx, etc)
What is the function of Osteoblasts and what do they make?
Form new bone. Make non-mineralized matrix (osteoid) for new bone formation.
What cells do Osteoblasts regulate?
Osteoclasts
Osteocytes are formed from what cell?
Osteoblasts
When does an Osteoblast become an Osteocyte?
When the surrounding bone matrix (osteoid) is mineralized
What is the name of the small cavity where osteocytes are located?
Lacunae
What are the majority of cells in the bone?
Osteocytes
What is the function of osteocytes?
Stimulate bone remodeling process by secreting enzymes which dissolve surrounding bone mineral and prepare for remodeling.
What do osteocytes sense?
Mechanical stimulants
What do osteocytes maintain?
Homeostasis of mineralized bone (calcification). P and Ca concentrations, receive nutrients from capillary blood.
Osteocytes are stimulated by these two, inhibited by this one, and communicate with others by what?
Stimulated= Calcitonin, physical stress
Inhibited= PTH
Communicate via= Gap junctions in canaliculi
Where are Osteoclasts located? What do they represent?
In Howship’s Lacunae. Represent areas of bone resorption.
What is the function of Osteoclasts?
Resorption of bone
What are the steps in osteoclast of bone resporption/break down?
Migrate and attach to bone, secrete acid and lytic enzymes, bone elements absorbed into osteoclast from microvilli, byproducts released into blood stream.
What happenst to the Osteoclast after resorption of bone?
Either goes dormant until needed again or apoptosis
What three things and conditions can Osteoprogenitor cells become?
- Osteoblasts under low strain and high oxygen conditions
- Cartilage under medium strain and low oxygen conditions
- Fibrous tissue under high strain
What are the two broad components of the ECM?
- Organic components
2. Inorganic components
Collagen FIbers, Proteoglycans, ECM proteins, and Cytokines/growth factors are examples of what?
Organic components of bone ECM
What makes Type 1 Collagen, what percent of organic component is it, and function?
Synthesized and secreted by Osteoblasts. 90% of organic component. Tensile strength of bone.
What are the functions of Proteoglycans, an organic component of bone ECM?
- Modulate fluid balance within bone by attracting calcium (via ion exchange)
- Compressive strength of bone
What is the function of ECM proteins, an organic component Of bone ECM?
Mineralization and bone formation
What are the 4 types of proteins involved in bone matrix?
- Osteocalcin
- Osteonectin
- Osteopontin
- Bone Almbuin
What is the function of Osteocalcin? What does it stimulate/attract? Where is this protein found and produced by what?
Regulation of bone density. Stimulates/attracts osteoclastic activity. Found in in bone matrix, produced by mature osteoblasts.
What stimulates Osteocalcin? What inhibits?
Stimulates=1,25 dihydroxyvitamin D3
Inhibits=PTH
Osteonectin and Osteopontin have a role in what?
Role bone mineralization
What are the two functions of Bone Albumin? Where is it found?
Found in bone matrix.
- Interstitial fluid balance of bone
- Transports hormones, ions, and other metabolites to/from bone cells
Where are Cytokines and Growth Factors? What is their function?
Embedded in matrix of bone.
Regulation/signaling for differentiation, activation, growth, and bone turnover.
Function of Bone Morphogenic Proteins? Where?
Embedded in bone matrix. Promote formation of osteoblasts from stem cells, osteogenesis in osteoblasts. Fills hole in bone that osteoclasts make.
What is organic bone component? What are the two that make them up?
Minerals. HAP and Calcium Phosphate.
What and where is Calcium Hydroxyapatite? What is it’s function?
Mineral which makes up inorganic bone component. Insoluable crystal that deposits in collagen fibers. Function in compressive strength of bone.
What are the two types of Bone Formation?
- Intramembranous Ossification
2. Endochondral Ossification
What kind of bones does Intramembranous Ossification form and where? What does it form without?
Forms “flat” bones in skull, face, mandible, and clavicle.
Forms without cartilage model.
What are the four steps of Intramembranous Ossification (long version, look at next card for short)?
- Cluster of osteoblasts forms ossification center within fibrous connective tissue membrane
- Osteoblasts secrete boney matrix in surrounding fibrous membrane which calficies and traps in osteoblasts
- Formation of trabeculae - osteoid form around invaginating blood vessels. Periosteum forms from mesenchyal cells.
- Bone collar of compact bone forms. Red marrow forms in trabeculae.
What are the four steps of Intramembranous Ossification? (short version)
- Osteoblasts form ossification center in fibrous connective tissue
- Crank our matrix to start clump of bone
- Forma trabeculae and gets blood supply
- Red marrow formed
What is Endochondral Ossification? What is its model? What replaces what?
Cartilage model of bone growth/formation. Bone replaces cartilage (cartilage does not become bone)!
Endochondral Ossification is responsible for which two kinds of bone growth?
- Longitudional bone growth during development
2. Appositional growth “widening” during VERY early development (when baby)
What are the two cartilaginous areas in an immature bone of Endochondral Ossification? Where are they located and what growth allows?
- Sphere Zone=around end of epiphysis. Allows growth of epiphysis.
- Physis (epiphyseal plate)=between metaphysis and epiphysis. Allows for longitudional growth. AKA growth plate.
Growth plate aka? On which kind of bone?
Epiphyseal Plate. On longitudional bone during growth.
Where and when are Chondrocytes found?
In the Endochonrial Ossification “Reserve Zone”. Earliest step.
What happens during Appositional Growth? What shape of bones does it happen to?
Long bones widen.
Age range when Growth Plates (epiphyseal plates) fuse? Any difference in male vs female?
14-21. Female earlier due to puberty.
What percent of the spine is full grown by age 8? Which grows faster in childhood -extremeties or axial skeleton?
80% by age 8.
Extremeties grow faster.
Osteoperosis is when what happens to osteoblasts and osteoclasts?
More osteoclastic activity than osteoblastic activity.
What are the 5 stages of bone remodeling?
- Activation
- Resorption
- Reversal
- Formation
- Quiesence
What is the stimulus and action of the Activation Phase of Bone Remodeling?
Stimulus: Anything that is probone growth. Hormone, drug, or physical stimulus.
Action: Activates resting osteoblasts to signal activation of osteoclastic activity.
What happens on the Resorption Phase of Bone Remodeling? In Compact Bone and Cancellous bone?
Osteoclasts breakdown bone and make resorption cavity.
Compact bone= cavity follows longitudional axis of Haversian canal
Cancellous bone=follows surface of trabeculae
What two hormones can slow/inhibit creating the resorption cavity in the Resorption Phase of Bone Remodeling?
Calcitonin and Estrogen
What do post-menopausal women lack that affects bones?
Lack Estrogen which allows osteoclasts to continue breaking down bone and prolong resorption.
What does Acidosis do to osteoclast resorption?
Promotes osteoclast resorption
Which cell upregulates and downregulates osteoclast activity?
Osteoblasts
Bone resorption is performed by which cell? What stimulates it?
Performing by active osteoclasts. Stimulates by RANKL, PTH, and other molecules.
Bone formation is performed by what two things/processes?
- Inhibiting osteoclasts
2. Stimulating osteoblasts
What inhibits Osteoclasts during bone formation?
OPG
What does Osteoclast activation stimulate?
Bone resportion
What are two molecules that stimulate bone resorption?
- RANKL
2. PTH
RANKL ligand is secreted by what two things and where does it bind to? What does it activate?
Secreted by Osteoblasts and Tumor Cells. Binds to RANK receptor on osteoclast precursor and mature osteoclast cells.
Activates osteoclasts.
What does PTH immediately stimulate in health bone? What does it stimulate in the long term?
Immediate=Short-term Ca++ release from bone fluid
Long-term=Stimulates osteoblasts to produce/release RANKL which stimulates osteoclasts
PTH can also be secreted by tumor cells and cause what?
Excess signaling of osteoclast resorption
What does Interluken-1 (IL-1) stimulate and cause? Where found?
Stimulates osteoclast differentiation which leads to bone resorption. Found near loose total joint implants which stimulate osteoclasts.
What does Osteoclast inhibition do to bones?
Decreases bone resorption
5 Molecules that inhibit bone resorption?
- OPG
- Calcitonin
- Estrogen
- IL-10
- Transforming Growth Factor Beta
What are OPG and how do they work? What produces them?
Inhibit bone resorption. Produced by Osteoblasts. Decoy receptors which bind to RANKL. Inhibit osteoclast differentiation, fusion, and activation.
What does Calcitonin do?
Inhibit bone resorption by decreasing calcium. Inhibit number and activity of osteoclasts.
What does Estrogen do to osteoclasts?
Inhibit bone resorption. Stimulates bone production and prevents resorption. Suppresses osteoclasts.
Osteolytic Bone Metastasis mediated by which pathway? Cancer cells directly produce what?
Mediated by RANK and RANKL pathway. RANKL produced directly by cancer cells.