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121 Cards in this Set
- Front
- Back
STFM
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skeletal tissue forming mesencyme
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3 Precursors of the skeleton (sources of STFM):
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1. Paraxial mesoderm
2. Lateral plate mesoderm 3. Ectoderm (neural crest) |
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What specifically does ectoderm form in the skeleton?
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structures in the head
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What does STFM form at the site of bone/cartilage formation?
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Preskeletal condensation
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3 Factors influencing STFM differentiation:
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-Epithelial-mesenchymal interactions
-Specific transcription factors -Growth factors |
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2 specific transcription factors influence STFM differentiation:
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Sox-9 (cartilage)
Cbfa-1 (bone) |
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A growth factor that acts during skeletal development:
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Bone morphogenetic factor (BMP)
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Specific component of paraxial mesoderm that contributes to STFM:
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Scleratome of somites
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Specific layer of lateral plate mesoderm that contributes to STFM:
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Somatic layer
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2 Pathways of bone formation:
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-Intramembranous ossification
-Endochondrial ossification |
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Each pathway starts with:
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Preskeletal Mesenchyme Condensation
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1st step in forming bones:
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STFM cells differentiate into CHONDROBLASTS and form cartilage
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Factor that directs differentiation of STFM cells forming bones:
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Cbfa-1 = intramembranous oss
Sox-9 = endochondrial oss |
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Steps 2-4 in forming cartilage:
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2. Chondroblasts -> Chondrocytes
3. Cytes secrete matrix 4. Cartilage forms; surrounding cells are Perichondrium |
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2 fates of cartilage:
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-Remain cartilage for life
-Form bone by intramembranous or endochondrial ossification |
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How does Intramembranous ossification get started?
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During preskeletal condensation, osteoblasts form directly by direction of cbfa-1
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What are qualities of bone that forms by intramemb ossification?
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Superficial, flat, and grows by adding new bone to edge.
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How does Endochondrial ossification get started?
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Cartilage forms first to provide a model.
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Qualities of bone formed by endochondrial ossification:
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-Deep
-Grows in a focused direction |
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Ossification centers are
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sites of collagen synthesis - where ossification occurs.
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What info do ossification centers give?
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Bone age - indicator of skeletal growth and maturation compared to actual age of patient.
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What is bone age?
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The amount of epiphyseal cartilage in skeleton
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Bone maturation that uses ossification centers:
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both - intramemb and endochond.
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2 types of ossification centers:
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Primary vs. Secondary
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Primary ossification centers:
-When in devo? -Where? |
Prenatal - located at CENTER of bones; radiates from there.
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Why does the skeleton have to develop prenatally?
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To support respiration
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Secondary ossification centers:
-When in devo? -Where? |
Pre/postnatal, postpuberal; located at ENDS of bones; growth happens from ends->in; disappear in 20's - 30's
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Axial skeleton consists of:
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-Vertebral column
-Ribs -Sternum -Skull |
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Vertebrae derive from:
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Scleratome mesenchyme - beginning at Somite 5
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Somitic mesoderm is from:
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Paraxial mesoderm
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3 components of somites:
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-Dermatome
-Myotome -Scleratome |
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4 steps in forming vertebrae:
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1. Lateral scleratome moves toward neural tube
2. Some scleratome moves close to notochord = perinotochordal sheath 3. Sclrtm condenses caudally; stay loose cranially 4. Perinotoch sheath arranges too but not in line with other |
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Loose potion of scleratome is associated with:
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spinal nerve and intersegmental artery
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Components of a primitive vertebrae:
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-Centrum
-Neural arches (pair) |
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What grows from the neural arches?
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Costal and transverse processes
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What does the centrum form from?
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Loose portion of perinotochordal sheath
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What is needed to form a centrum?
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2 adjacent somite pairs
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What do the neural arches form from?
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Dense portion of scleratome
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What does the compact portion of perinotochordal sheath become?
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Intervertebral disc
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What does the notochord become?
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Stays put where it is, as the Nucleus Pulposus
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___ pr of somites forms neural arches + intervertebral disc.
___ pr of somites forms centrum |
1 pair
2 pairs |
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Primitive vertebrae are formed by:
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Week 5-6
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Regionalization of the spine is achieved by:
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differential expression of hox genes along cranial/caudal axis
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What type of ossification do vertebrae undergo?
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Endochondrial
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How many 1' ossification centers develop in each vertebra?
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3-4
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What is the neurocentric junction?
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Line between centrum and neural arches; cartilage plate remains until 3-6 yrs old.
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When do secondary ossification centers form on vertebrae?
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Puberty
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Primary ossification centers:
____/centrum which ____ ___/neural arch |
2/centrum - usually fuse
1/neural arch |
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Regionalization signals:
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-Hox genes
-Retinoic acid |
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3 abnormalities of vertebral devo related to abnormal regionalization:
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1. Klippel-feil anomaly
2. Sacralization 3. Lumbarization |
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Klippel-feil anomaly:
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-Fused cervical vertebrae
-Short neck -Low hair line |
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Sacralization/Lumbarization:
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Change in # of a TYPE but not total number of vertebrae.
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Defects of Asymmetry:
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-Scoliosis - lateral curvature
-Kyphosis - front curvature -Lordosis - back |
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Dysraphism:
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General condition caused by failure of neural arches to fuse
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2 types of dysraphism:
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-Rachischisis (open)
-Spina bifida |
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What is Rachischisis?
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Condition where many vertebrae have unfused processes.
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What is Spina Bifida?
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Series of conditions where one or a few vertebrae have unfused processes
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What is the mildest form of spina bifida?
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Spina Bifida Occulta
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3 Defects of Formation of vertebrae:
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-Hemivertebrae
-Wedge-shaped Vertebrae -Unsegmented Bars |
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What can cause hemivetebrae to form?
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Failure of primary ossification centers to develop
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How do ribs develop?
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By lateral expansion of costal process in thoracic spine region
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How does the sternum develop?
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The ribs come together with 2 Sternal Bands and push them together to form the Sternum.
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What is the most common form of accessory ribs? Who is it more common in?
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Lumbar ribs - 3x more common in males.
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2 divisions of the skull:
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-Neurocranium (brain cavity)
-Viscerocranium (face/jaw) |
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Neurocranium consists of:
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-Chondrocranium (floor)
-Calvaria (skull cap) |
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Viscerocranium consists of 4 basic types of bones:
(how do they ossify?) |
-Ossicles/Styloid process via endochondral ossification
-Facial bones/Jaws via Intramembranous ossification |
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How many bones are in the skull?
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28
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Calvaria derives from:
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Neural crest
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Chondrocranium (floor) derives from:
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Paraxial mesoderm
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Face/jaws derive from:
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notochord
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How does each ossify:
-Calvaria -Chondrocranium |
Calvaria: intramembranous
Chondrochranium: endochondral |
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Chondrocranium:
-derived from? -How does it form? |
-Mesoderm (scleratom)
-Forms by fusion of several chondrogenic centers |
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What allows the chondrocranium to grow longitudinally?
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Spheno-ethmoidal and Spheno-occipital cartilage plates
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What is the Calvaria primarily derived from?
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Neural Crest Ectoderm
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What are Fontanelles?
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Intersections between cranial sutures that run perpendicular
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What are the 4 fontanelles, and what is each one's reference pt?
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Anterior - Bregma
Posterior - Lambda 2 Anterolateral - Pterion 2 Posterolateral - Asterion |
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What is the last fontanelle to close after birth?
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Anterior - between 1.5 - 2 yrs
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Face/Jaws
-Derived from? -How do they form? |
-Neural crest ectoderm
-Intramembranous ossification |
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What part of the viscerocranium forms by endochondrial ossification? Which arch?
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-Malleus/incus (Arch 1)
-Stapes/Styloid process (Arch 2) |
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What are the calvaria bones?
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-Interparietal part of occipital
-Parietal -Frontal |
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What are the first fontanelles to close?
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Posterior and Anteriolateral
-2 to 3 months |
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What are the next fontanelles to close?
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Posteriorlateral - 1yr
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And last?
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Anterior - 1.5 to 2 yrs
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What is a Dysraphic malformation of the skull referring to?
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Absence of calvaria bones, or an opening between them.
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What is a severe form of Dysraphic skull?
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Acrania - absence of the calvaria.
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What are 3 defects related to sutures?
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1. Craniosynostosis
2. Craniofacial Dysostosis 3. Cloverleaf skull |
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What is Craniosynostosis?
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Premature closure of the sutures
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What sutures do most Craniosynostoses involve?
-What sex is it more common in? |
50% - sagittal
30% - coronal More often in males |
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What defect is associated with Craniosynostosis?
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Defective FGF Receptor 1/2 genes
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What is the result of craniosynostosis?
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Assymetric skull
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What is Cloverleaf skull?
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Severe form of craniosynostosis; Skull grows in 3 directions
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What is a Dysraphic skull defect always associated with?
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Meroanencephaly
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What is microcephaly?
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Normal face, but small calvarium
-Assoc w/ defective cerebral hemisphere growth |
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What is an example of a Craniovertebral Junction defect?
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Occipitalization of the Atlas
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What are common features associated with craniovertebral junction defects?
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-Torticollis
-Short neck -Low nuchal hairline -Restricted movement of head on the spine |
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What could cause Craniovertebral Junction Defects?
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Defective Hox signalling and regional patterning
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What is Macrocephaly?
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Enlarged skull due to excess bone thickness
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Appendicular Skeleton consists of:
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-Limb girdles
-Limb bones |
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Appendicular skeleton is derived from:
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Somatic mesoderm
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2 Anomalies of Pectoral girdle formation:
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1. Cleidocranial Dysplasia
2. Sprengel Anomaly |
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What is Cleidocranial dysplasia?
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Hypo or Aplastic Clavicles
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What is Sprengel Anomaly?
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High set scapula - hypoplastic
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How do joints form?
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1. Cartilages approach
2. Perichondrium forms and surrounds future joint 3. Interzonal mesenchyme differentiates |
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What 3 types of joints can form from Interzone Mesenchyme differentiation?
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1. Fibrous
2. Cartilaginous (hyaline) 3. Synovial |
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What are the 2 components of Interzone mesenchyme in Synovial joints, what do they become?
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1. Peripheral - becomes ligaments
2. Central - becomes synovial cavity. |
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What do skeletal tissue dysplasias affect?
What problem causes these? |
-Growth in all/part of skeleton
-Abnormal extracellular matrix production |
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What does the term Chondrodystrophia describe?
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A group of disorders characterized by disproportionate growth.
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What is the most common chondrodystrophia?
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Achondroplasia - the most common type of dwarfism.
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What type of stature does a person with Achondroplasia have?
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-Normal trunk
-Short limbs -Large cranium, small face |
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What mutation is associated with Achondroplasia?
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FGF Receptor 3 gene
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Marfan Syndrome
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-spidery long fingers
-aortic aneurisms -joint hypermobility -defect of Fibrillin prodctn |
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Mucopolysaccharidoses
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-Lysosomal storage disorder
-Chronic, progressive, multisystem deterioration |
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Osteogenesis Imperfecta
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Collagen type I defect - brittle bones; respiratory problems
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Which chondrodystrophia is not dominant inheritance?
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Mucopolysaccharidoses
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2 Endocrine disorders that affect skeletal devo:
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-Hyperpituitarism (too much GH)
-Hypothyroidism (Cretinism) |
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What is Gigantism?
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-Rare form of hyperpituitarism
-If GH overproduction is prior to epiphyseal closure |
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What is the disease called if GH overproduction is AFTER epiphyseal closure?
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Acromegaly
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What features are associated with Acromegaly?
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Enlarged soft tissues and forehead
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What age determines whether Acromegaly or Gigantism results?
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-Prepuberty = Gigantism
-Postpuberty = Acromegaly |
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What are the common names for Hypopituitarism?
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-Cretinism
-Pituitary dwarfism |
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What symptoms result from cretinism?
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-Mental retardation
-Skeletal/ear anomalies -Younger bone age than actual age |