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29 Cards in this Set
- Front
- Back
Ossification: |
-The process of bone formation. -appears in the 6-week-old embryo and continues till about 25 years old. |
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There are 2 types of ossification: "IE" |
1. Intramembranous ossification 2. Endochondral Ossification |
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Intramembranous ossification: ("growth inside membranes") |
where bone develops from mesenchyme or fibrous connective tissue |
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Endochondral Ossification ("growth inside cartilage") |
where bone develops from a pre-exisintg cartilage model. |
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Process of intramembranous ossification STEP 1: The people migrate and form aggregations... |
-Mesenchymal cells migrate and form aggregations called OSSIFICATION CENTERS. -The mesenchymal cells differentiate into OSTEOBLASTS |
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The osteoblasts produce.... |
bone matrix which undergoes CALCIFICATION. |
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As the osteoblasts become encases in bone matrix they become .... |
osteocytes. |
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STEP 2: then the people extend their arms to their neighbors... |
- ossification centers extend outward called SPICULES "pointy-things; sticking out". - BVs grow and branch around spicules to support the bone tissue. |
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STEP 3: The people and the neighbors begin to hug. |
-continued ossification; -SPICULES FUSE together creating TRABECULAR NETWORKS. AKA SPONGY BONE. |
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Further remodeling produces.... |
the spongy bone, marrow cavities and COMPACT BONE- characteristic of mature bone. |
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Process of endochondrial ossification: |
-occurs in a cartilage pre-model of the bone that appears first in the embryo. |
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The cartilage model approximates the shape of the future bone and grow by both.... |
INTERSTITIAL and APPOSITIONAL growth. |
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Step 1: The Smith family gets larger so they sell their home.. |
-Chondrocytes in the center BECOME LARGER and the surrounding cartilage matrix becomes CALCIFIED. |
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These chondrocytes undergo... |
programmed death leaving behind CAVITIES within the cartilage matrix. |
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Step 2: They purchase a new home on Periosteum Way.... |
- the PERICHONDRIUM of the cartilage model becomes transformed into a PERIOSTEUM("around the bone") as an OSTEOGENIC LAYER forms. |
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Periosteum--->
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produces a THIN COLLAR OF BONE AROUND THE DIAPHYSIS ("SHAFT") |
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Step 3: Their smaller home did not sell, so squatters quickly came to stake their claim... |
-BVs & OSTEOPROGENITOR CELLS penetrate in the calcified cartilage matrix. (center of diaphysis) -inside becomes OSSIFICATION CENTER -OSTEOBLASTS can produce SPONGY BONE -this becomes the SECONDARY OSSIFICATION CENTER. |
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Step 4: The Smiths remodel the old home... |
-remodling occurs: OSTEOGENESIS -a cavity results as the bone is remolded = MARROW CAVITY. -increase in LENGTH and DIAMETER |
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Increasing the length of the developing bone: diaphysis epiphysis (epiphyses) metaphysics epiphyseal plate |
- the shaft of the long bone -two expanded ends -the flared portion between the epiphysis and the diaphysis -a piece of cartilage in the epiphysis where growth in the length of the bone occurs |
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Step 5: The second story remodel is now finished... |
SECONDARY OSSIFICATION CENTERS appear in the epiphyses in a manner similar to that described above for the primary ossi. center. |
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Step 6: Articular Cartilage and Zones |
-Ossi. proceeds, the epiphyses become filled w/ spongy bone and only a thin piece of hyaline cartilage left = ARTICULAR CARTILAGE. -thin plate of cartilage, EPIPHYSEAL PLATE, now separate the bone of the epiphyses from that of the diaphysis. -growth in length of the bone occurs at the epiphyseal plate as is evidenced by the appearance of zones within the cartilage. |
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1. Zone of reserve or resting cartilage: |
-chondrocytes here exhibit no division or active matrix production |
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2. Zone of proliferation |
-chondrocytes undergo CELL DIVISION and arrange themselves in distinct columns that are parallel to the direction of growth. |
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3. Zone of Hypertrophy |
-chondrocytes ENLARGE and compress the cartilage matrix surrounding them. **not good for the chondrocytes** |
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4. Zone of Calcification |
enlarged chondrocytes undergo programmed cell death (lysis) and die; become calcified. |
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5. Zone of resorption (a.k.a) ossification |
-the cavities left by dead chondrocytes are invaded by blood vessels that bring osteoprogenitor cells with them. -Bone is produced on the surface of calcified cartilage as it undergoes RESORPTION. |
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Step 7: |
-bone increases in length as long at the rate of cartilage production equals that rate by which it is replaced by bone. -as bone matures the rate of bone production "catches up" with the rate of cartilage production and the cartilage that was the epiphyseal plate is replaced by an EPIPHYSEAL LINE. |
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Increasing the diameter of the developing bone: |
-the diameter increases by APPOSITIONAL GROWTH. |
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-Osteoblasts in the cellular layer of the periosteum add success layers of bone called... |
CIRCUMFERENTIAL LAMELLAE ("layers") -at the same time, osteoclasts on the interior surface resorb bone and widen the marrow cavity. -the final result is an increase in both the diameter and marrow cavity of the bone. |