Glossary of CTO 10 bone development
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- Primary Bone
- first type of bone produced in the fetus or during repair of a fracture
- Secondary Bone
- mature bone, both types (compact/cortical or spongy/trabeccular) laid out in well defined layers
- 2 Mechanisms of Bone Development
- Intramembranous Ossification
- Intramembranous Ossification
- osteoblasts secrete the matrix which is then mineralized
- Endochondral Ossification
- bone is deposited on a pre-exisiting cartilage matrix
- bone tissue that appears first in either mechanism of bone formation
- woven bone
- Characteristics of Primary Bone
- non-lamellar, random weave of bone, abundant osteocytes and low mineral conent, temporary, will be replaced by secondary bone tissue
- Primary Unit of Compact Bone, lamellae arranged in circular pattern around Haversian Canal
- Osteon or Haversion System
- arrangement of collagen fibers in one lamella
- parallel (but perpindicular in adjacent lamella)
- lacunae between and sometimes within the lamellae contain...
- small channels between the lacunae that house the cellular processes of osteocytes and facilitate communication.
- lamellae associated with the osteon
- outer circumferential
- Outer circumferential lamellae
- found deep to the periosteum
- inner circumferential lamellae
- surround the marrow cavity
- intertitial lamellae
- triangular or irregularly shaped lamellae that are remnats of osteons that were destroyed during growth and remodeling
- Volksman's Canals
- connections between Haversion canals and the periosteum/endosteum
- characteristics of spongy bone
- trabeculae or spicules
trabeculae contain irregular or circular lamellae
does not usually contain osteons
- intramembranous ossification is responsible for...
- process responsible for most flat bones including those in cranial vault
- where does intramembranous ossification takes place?
- highly vascularized mesenchymal tissues
- in intramembranous ossification what cells migrate to region where bone is to form
- mesenchymal cells
- in intramembranous ossification.. into what types of cells do groups of mesenchymal cells differentiate?
- osteoblasts (via an intermediate osteoprogenitor stage)
- what do osteoblast secrete?
- what determines the location of the primary ossification center?
- region of initial osteogenesis
- at what point are osteocytes formed?
- when osteoblasts become trapped in surrounding newly-formed matrix
- islands of devleoping bone
- orientation of collagen in primary bone spicules
- what happens in the connective tissue among the newly formed spicules?
- growing blood vessels penetrate the CT and undifferentiated mesenchymal cells give rise to bone marrow cells
- in what manner to the ossification centers grow?
- radially, fusing to replace original connective tissue
- what happens to the portion of the bone that does not undergo ossification
- this part of the bone becomes the periosteum and the endosteum
- type of ossification that forms short and long bones
- endochondral ossification
- hyaline cartilage model
- model that begins the process of endochondral ossification, resembles small version of bone to be formed
- how are trabeculae formed in hyaline cartilage model?
- chondracytes within the shaft hypertrophy, reducing the cartilage matrix to slender trabeculae, cartilage matrix calcifies with large spaces
- first bone is formed by...
- intramembranous ossification within the perichondrium surrounding the diaphysis
- at what point and how does the periosteum form?
- when the perichondrium becomes vascularized and devleops osteogenic potential, osteblasts begin secreting bone, forming bone collar
- how does the the central cavity in cartilage form?
- periosteum prevents diffusion of nutrients to the condrocytes causing them to die forming...
- what is the osteogenic bud?
- osteoprogenitor cells, hematopoetic cells and blood vessels
- how does the osteogenic bud enter the concavities of the cartilage model?
- osteoclasts form homes in the bone collar
- what forms a continuous layer on calcified cartilage?
- osteoblasts, secrete osteoid onto it
- primary ossification center is where?
- in the diaphysis, progresses toward epihysis
- what forms the marrow cavity?
- osteoclastic activity in teh center of the forming bone.
- secondary ossification center
- in epiphysis, pgoresses much like the other, but does not form a bondy collar
- where does cartilage remain?
- 1. articular cartilage- hyaline cartilage covering joint surfaces
2. epiphyseal plate (continues to grow and is continuously replaced by bone matrix- resulting in elongation of bone)
- proliferation occurs at what aspect of the epiphyseal plate?
- epiphyseal aspect (top)
- replacement by bone occurs on what aspect of the epiphyseal plate?
- diaphyseal aspect
- Zones of epitheseal plate
- resting zone
zone of proliferation
zone of hypertrophy
zone of ossification
- resting zone
- hyaline cartilage without morphological changes
- zone of proliferation
- chondrocytes dividing rapidly that form columns of stacked cells parallel to the long axis of the bone
- zone of hypertrophy and calcification
- large chondrocytes whose cytoplasmhas accumulated gylcogen and narrow areas of matrix between lacunae
- zone of ossification
- osteoprogenitor cells invade the area and differentiate into osteoblasts, secrete bone matrix onto the calcified cartilage matrix
- Bone length depends upon what
- activity in the epiphyseal plate
- most important stimulus of bone growth (epiphyseal plate activity) in infancy and childhood
- growth hormone (somatotropin) released from anterior pituitary
- pituitary gigantism
- excessive height- resulting from excessive amount of growth hormone
- diminished height (deficits of growth hormone)
- what determines the end of bone growth?
- when the cartilage of the epiphyseal plate ceases proliferation and bone development continues to unite the diaphysis and epiphysis
- appositional grwoth
- increase in bone width, pone is produced by the periosteum (by intramembranous ossification) on the external surface of bone collar
- vitamin D deficiency
- prevents calcium absorption from teh GI tract resulting in rickets (kids) osteomalacia (adults) osteoid is produced, but calcium salts are not deposited so bones soften and weaken
- bone remodeling
- process of selective bone resorption and esposition- essential for continually reshaping bones in response to changing forces
- in a growing person bone deposition is less than, greater than, or equal to bone resportion
- GREATER THAN
- what causes osteopeorosis?
- bone resorption exceeds bone deposition
- How is fracture repair initiated
- 1. blood from damaged vessels forms a 2. clot, damaged matrix, dead cells removed by macrophages.
3. granulation tissue forms in the site of clot and condenses into CT and later into a fibrocartilagenous callus
(at same time..)
Osteoprogenitor cells of periosteum are activated and become osteoblasts that begin to deposit new bone (meshwork of trabeculae of primary bone) callus around fracture site
4. Endosteum cells activated and deposit bone around cartilagenous callus, that is slowly eroded and replaced by bone (endochondral ossification)
5. spongy bone is transformed into combact bone by osteoblastic deposition of matrix
6. osteoclasts reabsorp excess bone- and reestablish marrow cavity
- calcium homeostasis
- bones release calcium when blood levesls decrease below normal, store calcium in matrix when blood leves are high
- parathyroid hormone, produced in response to depressed calcium levels, triggers and increase in blood calcium through multiple paths
- Vitamin D
- may also play a role in calcium regulation at times of depressed levels
- acts directly on osteoclasts to inhibit their resportive activity (lower free calcium levels)
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