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61 Cards in this Set

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  • Back
Bones (General)
The organs of the skeletal system, composed of bone tissue (a specialized form of connective tissue), cartilage, fibrous CT, adipose tissue, nerves, lymphatics, and blood vessels.
Bone Tissue
A specialized form of connective tissue containing (like all CT) cells and ECM. Bone is unique in that it contains mineralized ECM that produces extremely hard tissue.
Functions of Bone
Framework for the body (and support for soft tissues), Protection of internal organs, Locomotion (facilitates movement by providing leverage for muscle contraction), Mineral Storage (calcium and phosphorous are stored and mobilized when needed), Hematapoeisis (Blood cell-producing lines are stored in bone marrow), and Energy storage (in adipose tissue of the marrow).
How are osteoblasts derived/what is their origin?
Osteoblasts' precursor cells, osteoprogenitor cells, originally arise from mesenchymal stem cells. The first osteoblasts differentiate in the periosteum and form bone collar. They can also potentially originate in bone marrow.
CT lining the periphery of a bone.
CT lining the internal surfaces of a bone. In the long bone, it lines the medullary cavity. Like periosteum, it consists of two layers: a protective outer fibrous layer and an osteogenic layer.
Where Are Osteoblasts Found?
They are found in both the periosteum and endosteum of bone.
Functions of Osteoblasts
Synthesize and secrete collagen fibers and initiate the process of calcification.
How are osteocytes derived/what is their origin?
Osteocytes are of mesenchymal origin. They are terminally differentiated osteoblasts that have become trapped by matrix secretion.
Functions of Osteocytes
Responsible for maintaining the bone tissue, they are found in mature bone cells and no longer secrete matrix.
Functions of Osteoclasts
Digestion of bone matrix (osteolysis) in a process called bone resorption.
Why do osteoclasts have many nuclei?
They are derived from the fusion of many monocytes (WBC type).
Where are osteoclasts found?
They are concentrated in the endosteum.
What is the ruffled border of the osteoclast?
The ruffled border is folded plasma membrane on the side of the cell that faces the bone surface. Here the osteoclast secretes lysosomal hydrolases and hydrogen ions.
Lysosomal Hydrolases (in osteoclasts)
Digestive enzymes to digest bone matrix
Why are hydrogen ions secreted from the ruffled border of osteoclasts?
To create an acidic environment to eat away the ECM.
Unmineralized bone matrix containing fibers, glycoproteins, and proteoglycans.
What are the components of the ECM of bone?
Bone ECM is made up of ~1/3 organic and ~2/3 inorganic components. the organic components secreted by osteoblasts include collagen fibers, and non-collagenous matrix proteins
What kinds of non-collagenous matrix proteins are found in bone?
Proteoglycans, glycoproteins, bone-specific vitamin k-dependent proteins, and growth factors and cytokines.
Describe the collagen fibers of the ECM of bone matrix.
They are predominately Type 1 (with some of Type 5 and the other types). They function to provide bone with resilience and ability to resist stretching and twisting.
What is the role of proteoglycans in the ECM of bone?
They contribute to the compressive strength.
What is the role of glycoproteins in the ECM of bone? Give two examples.
They glue bone cells/fibers to mineralized ground substance. Osteopontin mediates bone cell to matrix attachment and osteonectin links collagen and bone minerals.
Name one kind of bone-specific vitamin-K dependent protein in the ECM of bone and describe its function.
Osteocalcin captures calcium from circulation for calcification. It attracts and stimulates osteoclasts for remodeling.
What is the role of growth factors and cytokines in the ECM of bone? Give some examples of growth factors/cytokines found in the ECM of bone.
Growth factors and cytokines in the ECM of bone are regulatory. Examples are insulin-like growth factor (IGF), tumor necrosis factor (TNF-alpha), transforming growth factor beta (TGF-beta), interleukins (IL-1, IL-6), and bone morphogenic proteins (BMP's).
What are bone morphogenic proteins (BMP's) and what do they do in the ECM of bone?
BMP's in the ECM of bone are unique growth factors that stimulate differentiation of mesenchymal cells into osteoblasts.
What are the inorganic components of the ECM of bone?
ECM of bone has two primary inorganic constituents, calcium phosphate and calcium hydroxide (together they interact to produce hydroxyapatite that is later crystallized). Bone also contains small amounts of magnesium, fluoride, and sodium. These minerals give bone its characteristic hardness and ability to resist compression.
Hydroxyapatite crystals
Crystals formed in the ECM of bone by the combination of calcium phosphate and calcium hydroxide. They are hard and resistant
What are the two types of mature bone?
Compact and cancellous.
What is compact bone and what kind of stresses characterize its locations?
An outer layer of solid and densely packed bone located where stresses are limited to one direction. It forms the diaphysis and is true Haversian bone. It provides a rigid "wall" to support the bone itself and the tissues of the body.
What is cancellous bone and what kind of stresses characterize its locations?
(aka Spongy or trabecular bone). An inner layer of bone with a honeycomb pattern located where stresses are weaker or multi-directional. It fills the epiphysis and forms a narrow rim around the medullary cavity.
Describe the three important regions of the long bone.
The epiphysis (two per bone: one proximal, one distal) are the dilated "ends" of the bone. The diaphysis is the tubular shaft of the bone. The metaphysis (two per bone: one proximal, one distal) is the transition zone between the epiphysis and diaphysis.
What is found in the region of the epiphysis in young animals and not mature animals?
The epiphyseal growth plate cartilage that consists of actively growing hyaline cartilage. It closes when growth stops.
Name the major structures of the long bone.
Important structures include the periosteum, articular cartilages, spongy bone, compact bone, medullary cavity, endosteum, nutrient artery, and the nutrient foramen.
Describe the periosteum of the long bone.
The periosteum is CT that covers the entire surface of the bone except the articular cartilages. It consists of two layers: the outer fibrous layer (for protection and attachment of ligaments/tendons) and the inner cellular layer (comprised of osteoprogenitor cells). The periosteum provides sites for blood vessels to pass into and out of bone.
What are articular cartilages of the long bone?
Hyaline cartilage pads at the ends of bone which help absorb shock and reduce friction between adjacent articulating bones.
Medullary Cavity
The space within the diaphysis that contains bone marrow.
Nutrient Foramen
The nutrient foramen is a hole in the diaphysis through which passes the major nutrient blood vessel. The area surrounding this was the primary ossification center.
Describe Haversian systems (osteons) found in compact bone.
Haversian systems are composed of numerous cylinders aligned in parallel along the long axis of the bone that increase the bone's resistance to stress.
Name some components of Haversian systems (osteons).
Components of osteons include central (Haversian) canals, osteocytes, caniculi, bone llamellae, and Volkmann's canals.
Central (Haversian) Canals
Contain blood vessels, nerves, and lymphatics.
What are canaliculi and what processes/functions do have a role in?
Narrow passageways that connect lacunae. They play a role in nutrient exchange, communication between bone cells, bone resistance, and shock absorption.
Bone Lamellae
Concentric layers of bone matrix.
Volkmann's Canals
Canals running perpendicular to Haversian systems that connect adjacent osteons.
How is cancellous bone arranged compared to the arrangement of compact bone? Which is more organized?
Cancellous bone is arranged in a 3-D lattice of trabeculae (which are arranged along the lines of greatest force to the bone). It is poorly organized compared to compact bone and contains no osteons (blood vessels run through the trabecular bone but no Haversian or Volkmann's canals).
What is meant by the term woven bone? What are some of its characteristics?
Woven bone refers to primary bone (or immature bone) formed during fetal development and absent in adults (except in pathological conditions). It does not contain lamellae, has a disorganized array of collagen and irregular mineralization pattern, and the lacunae are not arranged in parallel rows as they are in mature lamelar bone.
What is meant by the term lamellar bone? What are some of its characteristics?
Lamellar bone is mature (secondary) bone composed of collagen fiber bundles arranged in organized sheets (lamellae) in the same direction. It has lacunae in parallel rows. Both compact and cancellous bone types are lamellar bone.
What is the function of bone development (osteogenesis or ossification) in the embryo, neonate, and adult?
In the embryo it forms the skeleton, n the neonate it occurs as part of bone growth, and in the adult it occurs as part of bone remodeling and repair.
What is the difference between ossification and calcification?
Ossification is the process of replacing other tissues with bone, while calcification (mineralization) is the deposition of calcium salts in the collagen framework (this occurs in ossification).
What are the two mechanisms of bone development? What similarities exist between them?
The two mechanisms are intramembranous ossification and endochondral ossification. Both processes begin with proliferation and aggregation of mesenchymal cells at the site of future bone in the embryo. They also both initially produce woven bone that is later remodeled to produce mature lamellar bone.
Where do the two mechanisms of bone development take place?
Intramembranous ossification occurs in the CT membrane while endochondral ossification occurs in cartilage.
Describe intramembranous ossification and give examples of bones formed in this manner.
It is the simpler method, forming without a cartilage template and is used by the flat bones of the skull, face, mandible, and clavical. Bones form directly from mesenchyme as mesenchymal cells are converted to osteoblasts, which produce the matrix (osteoid), which eventually becomes mineralized. The osteoblasts are then trapped in the matrix and become osteocytes.
Describe endrochondral ossification and give examples of bones formed in this manner.
This involves a cartilagenous model and is used by most bones of the body (the long bones and parts of the axial skeleton that bear weight such as vertebrae). Boe forms by differentiation of mesenchymal cells to chondroblasts that migrate to the center of the shaft and produce the cartilage template. Osteoprogenitor cells then differentiate into osteoblasts and make osteoid and bone replaces the cartilage.
How does a cartilage model, once formed, grow?
A cartilage model grows by appositional and interstitial growth. A primary ossification center develops in the center of the shaft (diaphysis) and secondary ossification centers later arise and form the physis (at/after birth).
What types of growth lead to the lengthening/thickening of bone?
Lengthening occurs by longitudinal growth, thickening occurs by appositional growth.
When might bone modeling or bone remodeling occur? Differentiate between the two.
Bone modeling describes changes in bone shape seen during normal growth, altered mechanical use, or disease. It is an adaptive response to changing stresses on the bone. Remodeling is seen in the constant replacement of old bone with new bone (a homeostatic mechanism).
Why does bone shape change during bone modeling and not during bone remodeling?
In bone modeling, bone resorption and formation both occur at different sites with osteoblasts and osteoclasts act independently so the bone morphology (shape) changes. In bone remodeling, sequential action of osteoblasts and osteoclasts occurs at the same site so there is no change in bone morphology.
What are the four zones of the epiphyseal growth plate cartilage?
1) Zone of resting cartilage
2) Zone of proliferation
3) Zone of hypertrophy
4) Zone of calcification
What allows for the microscopic repair of damaged bone?
Bone remodeling.
Upon what structure does longitudinal bone growth depend?
The lengthening of long bones depends on the presence of epiphyseal cartilage (a growth plate). Activity in this plate is the only means by which the diaphysis can increase in length. Lengthwise growth of the bone stops when the growth place is completely replaced by bone.
By what process does longitudinal bone growth occur?
Longitudinal bone growth occurs by endochondral ossification.
Describe what is happening in the stages of endochondral ossification.
Chondrocytes proliferate and proceed through stages of maturation and hypertrophy. Following hypertrophy, the surrounding matrix and vascular tissue calcify. The hypertrophic chondrocytes degenerate and give way to invading osteoblasts. Bone and bone marrow replace calcified cartilage at the metaphysis, pushing the epiphyseal region away from the metaphysis and diaphysis.