28 February Lecture
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Created by:
kmcdaniel223 on March 12, 2011
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33 terms
Terms | Definitions |
|---|---|
 What are the two processes that can produce bone? | -intramembranous ossification -endochondral ossification |
| Intramembranous ossification | -a process of bone development in which there is no cartilage precursor; rather, the bone develops directly from a sheet of condensed mesenchyme |
| Endochondral ossification | -a process of bone development in which the bone is preceded by a model of hyaline cartilage in roughly the shape of the bone to come, and the cartilage is then replaced by osseous tissue |
| Mesenchyme | -a type of undifferentiated loose connective tissue -the embryonic origin of all adult connective tissues (including fibrous CT, adipose tissue, blood, bone, and cartilage) |
| What are the 3 embryonic sources for osteogenic mesenchyme? | -sclerotome -somatic mesoderm -neural crest cells |
| What parts of the skeleton does sclerotome give rise to? | -ribs and vertebrae (endochondral ossification) |
| What parts of the skeleton does somatic mesoderm give rise to? | -bones of the limbs (endochondral ossification) |
| What parts of the skeleton do neural crest cells give rise to? | -bones of the cranium and face (intramembranous ossification) |
| Which parts of the skeleton form by intramembranous ossification? | 1. Flat bones of the cranium and face, ie- -neurocranium -viscerocranium (including mandible) 2. Clavicles |
| Which parts of the skeleton form by endochondral ossification? | -most bones -any bones that form inferior to the bones of the cranium and face, other than the clavicles |
| Stages of intramembranous ossification (1-6) | 1. Mesenchyme condenses into a layer of soft tissue. 2. Mesenchymal cells enlarge and differentiate into osteogenic cells 3. Regions of mesenchyme become a network of soft sheets called trabeculae 4. Osteogenic cells gather on trabeculae and differentiate into osteoblasts 5. Osteoblasts first produce the osteoid (collagen), then secrete hydroxyapatites through calcification/mineralization 6. Some osteoblasts become trapped in the matrix (within lacunae and canaliculi) and are now osteocytes |
| Stages of intramembranous ossification (7-10) | 7. Some trabeculae persists as permanent spongy bone, and are formed into lamellae 8. Other trabeculae are transformed into compact bone through the formation of osteons 9. Some surface osteoblasts are used to make the bone cell layer of periosteum 10. Surrounding mesenchymal cells differentiate into fibroblasts, then make the fibrous CT that forms the outer layer of the periosteum |
| What does the embryonic skeleton look like? (what is it comprised of?) | -membranous mesenchyme -hyaline cartilage |
| Chondrification | -first stage of endochondral ossification -bone is modeled in cartilage -occurs during embryonic life -hyaline cartilage is used |
| Chondroblasts | -secrete cartilage matrix during endochondral ossification -derived from mesenchyme |
| Primary ossification | -occurs during fetal life -blood vessels penetrate the center portion of the bone model -center of model is hollowed out and filled with blood and stem cells -stem cells give rise to osteoblasts and osteoclasts -osteoblasts begin to deposit osteoid tissue -cartilage death progresses in a wave towards the end of the bone -osteoblasts dissolve calcified cartilage |
| Secondary ossification | -occurs during post-fetal life -blood vessels piercing the cartilage of the epiphysis -center of epiphysis hollowed out and filled with blood and stem cells -stem cells give rise to osteoblasts and osteoclasts -osteoblasts begin to deposit osteoid tissue, etc. |
| When is secondary ossification complete? | -at 18 for girls -at 21 for guys |
| What is the growth plate/epiphyseal plate? which humans have one? | -separates marrow cavities of the epiphysis and diaphysis -zone where the bones grow in length -found in children and adolescents |
| What is the growth plate/epiphyseal plate replaced with in adults? | -epiphyseal line |
| What are the five zones within the epiphyseal plate? | -zone of resting cartilage -zone of proliferation -zone of hypertrophy -zone of calcification -zone of bone deposition |
| Zone of resting cartilage | -hyaline cartilage chondroblasts are at rest -"hanging out," sitting around |
| Zone of proliferation | -hyaline cartilage chondroblasts begins to divide by mitosis -cells proliferate, more cartilage cells result -begin to produce cartilage matrix |
| Zone of hypertrophy | -cartilage chondroblasts cease to multiply -cartilage chondroblasts begin to hypertrophy (enlarge) |
| Zone of calcification | -chondroblasts begin to die off -as the chondroblasts die off, the surrounding cartilage matrix becomes calcified -(occurs through series of biochemical events that we don't need to know about) -(has nothing to do with step two of bone deposition) |
| Zone of bone deposition | -chondroblasts die and leave lacunae -calcified cartilage remains--built of ragged ridges, struts and beams -area is invaded by blood vessels, which deliver bone cells and nutrients to the area -bone cells create osseous matrix using the calcified cartilage as a template/grid |
| hypertrophy | -enlargement of cells |
| Which hormone controls growth of the epiphyseal plate cartilage during childhood? | -human growth hormone -released primarily from birth until age 2/3 |
| Where is human growth hormone released from? | -pituitary gland |
| Which hormone controls growth of the epiphyseal plate during adolescents? | -sex hormones -testosterone and estrogen |
| What seals off the epiphyseal plate at the end of puberty? | -testosterone and estrogen |
| Periosteal bud-what does it contain? | - consists of blood vessels, lymph vessels and nerves -ultimately carries hemopoietic cells, osteoblasts and osteoclasts into the diaphysis or epiphysis |
| Periosteal bud-what does it do? | -invades cavity within diaphysis during primary ossification -invades cavity within epiphysis during secondary ossification |
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