Chapter 10 Flashcards
In general, the skeletal system develops from ____ and ____ (parietal layer) mesoderm and from neural crest
paraxial and lateral plate
Paraxial mesoderm forms a ___ series of tissue blocks on each side of the neural tube, known as ___ in the head region and somites from the occipital region caudally
segmented - somitomeres
Somites differentiate into a ventromedial part, the ___, and a dorsolateral part, the ___
sclerotome - dermomyotome
At the end of the fourth week, sclerotome cells become polymorphous and form loosely organized tissue, called ___, or embryonic connective tissue
mesenchyme
Mesenchyme may become fibroblasts, chondroblasts, or ____ (bone-forming cells)
osteoblasts
In some bones, such as the flat bones of the skull, mesenchyme in the dermis differentiates directly into bone, a process known as ____
intramembranous ossification
The skull can be divided into two parts: the ____, which forms a protective case around the brain, and the ____, which forms the skeleton of the face
neurocranium - Viscerocranium
Neurocranium, Divided into two portions: (1) the membranous part, consisting of ___, which surround the brain as a vault, and (2) the ____, or _____, which forms bones of the base of the skull
flat bones
cartilaginous part - chondrocranium
The result is formation of a number of flat, membranous bones that are characterized by the presence of needle-like ___
bone spicules
At birth, the flat bones of the skull are separated from each other by narrow seams of connective tissue, the ___
sutures
Ossification centers appear in these cartilage models, and the bone gradually ossifies by ____
endochondral ossification
The most prominent of these is the ___, which is found where the two parietal and two frontal bones meet
anterior fontanelle
At points where more than two bones meet, sutures are wide and are called ___
fontanelles
Sutures and fontanelles allow the bones of the skull to overlap (____) during birth
molding
Those that lie in front of the rostral limit of the notochord, which ends at the level of the pituitary gland in the center of the sella turcica, are derived from neural crest cells. They form the ____.
prechordal chondrocranium
Those that lie posterior to this limit arise from occipital sclerotomes formed by paraxial mesoderm and form the ____
chordal chondrocranium
The first arch gives rise to a dorsal portion, the ___, which extends forward beneath the region of the eye and gives rise to the ___, the ___, and part of the ____
maxillary process - maxilla, zygomatic bone, temporal bone
The ventral portion, the ____, contains the Meckel cartilage.
mandibular process
The ventral portion, the mandibular process, contains the ___.
Meckel cartilage
Mesenchyme around the Meckel cartilage condenses and ossifies by intramembranous ossification to give rise to the ___
mandible
The Meckel cartilage disappears except in the ____ligament
sphenomandibular
The dorsal tip of the mandibular process, along with that of the second pharyngeal arch, later gives rise to the ___, ___, and the ___
incus, the malleus, and the stapes
Originating in the neuroectoderm form the facial skeleton and part of the skull. These cells also constitute a vulnerable population as they leave the neuroectoderm; Often a target for teratogens
Neural Crest Cells
The cranial vaultfails to form [___], and brain tissue exposed to amniotic fluid degenerates, resulting in anencephaly
[cranioschisis]
The cranial vaultfails to form [cranioschisis], and brain tissue exposed to amniotic fluid degenerates, resulting in _____
anencephaly
____ is caused by failure of the cranial neuropore to close
Cranioschisis
Children with relatively small defects in the skull through which meninges and/or brain tissue herniate [___ and ____] may be treated successfully
cranial meningocele and meningoencephalocele
Caused by premature closure of one or more sutures
Craniosynostosis
Loss of function mutations in EFNB1 causes ___, characterized by coronal suture synostosis and hypertelorism
craniofrontonasal syndrome
Mutations in MSX2 cause ____ that can affect a number of sutures
Boston-type craniosynostosis
mutations in TWIST1 cause ____, characterized by coronal suture synostosis and polydactyly
Saethre-Chotzen syndrome
___ and ___ play important roles in most of skeletal development
Fibroblast growth factors [FGFs] and fibroblast growth factor receptors [FGFRs]
Signaling is mediated by the receptors, which are ____, each of which has three extracellular immunoglobulin domains, a transmembrane segment, and a cytoplasmic tyrosine kinase domain
transmembrane tyrosine kinase receptors
___ is expressed in the cartilage growth plates of long bones and in the occipital region.
FGFR3
Premature closure of the coronal sutures [20% to 25% of cases] results in a short skull called ____
brachycephaly
Mutations in these receptors, which often involve only a single amino acid substitution, have been linked to specific types of ____ [FGFR1, FGFR2, and FGFR3] and several forms of ___ [FGFR3]
craniosynostosis - skeletal dysplasia
The shape of the skull depends on which of the sutures closes prematurely. Early closure of the sagittal suture [57% of cases] results in frontal and occipital expansion, and the skull becomes long and narrow [____]
scaphocephaly
If the coronal sutures close prematurely on one side only, then the result is an asymmetric flattening of the skull called ___
plagiocephaly
___ is the most common neonatal lethal form of skeletal dysplasia [1/40,000 live births]
Thanatophoric dysplasia
_____, the most common form of skeletal dysplasia [1/20,000 live births], primarilyaffects the long bones. Other skeletal defects include a large skull [megalocephaly] with a small midface, short fingers, and accentuated spinal curvature
Achondroplasia [ACH]
There are two types; both are autosomal dominant. ____ is characterized by short, curved femurs with or without cloverleaf skull; ___ individuals have straight, relatively long femurs and severe cloverleaf skull caused by craniosynostosis.
Type I - type II
Another term for cloverleaf skull is ___. It occurs when all of the sutures close prematurely, resulting in the brain growing through the anterior and sphenoid fontanelles
kleeblattschadel
___is an example of a generalized dysplasia of osseus and dental tissues that is characterized by late closure of the fontanelles and decreased mineralization of the cranial sutures resulting in bossing [enlargement] of the frontal, parietal, and occipital bones
Cleidocranial dysostosis
A typical vertebra consists of a ___ and ___ (through which the spinal cord passes),___, ____, and usually a ___
vertebral arch and foramen, a body, transverse processes, spinous process
____, another autosomal dominant form ofskeletal dysplasia, appears to be a mildertype of ACH
Hypochondroplasia
___ is caused by congenital hyperpituitarism and excessive production of growth hormone
Acromegaly
__ is usually an abnormality in which the brain fails to grow and, as a result, the skull fails to expand .
Microcephaly
During the 4th week, sclerotome cells migrate around the spinal cord and notochord to merge with cells from the opposing somite on the other side of the neural tube. As development continues, the sclerotome portion of each somite also undergoes a process called ___
resegmentation
Mesenchymal cells between cephalic and caudal parts of the original sclerotome segment do not proliferate but fill the space between two precartilaginous vertebral bodies. In this way, they contribute to formation of the ___
intervertebral disc
Notochord regresses entirely in the region of the vertebral bodies, it persists and enlarges in the region of the intervertebral disc. Here, it contributes to the ___, which is later surrounded by circular fibers of the annulus fibrosus
nucleus pulposus
Later, two secondary curves are established: the cervical curvature, as the child learns to hold up his or her head, and the ___, which forms when the child learns to walk
lumbar curvature
As the vertebrae form, two primary curves of the spine are established: the ___ and ___
thoracic and sacral curvatures
The process of formation and rearrangement of segmental sclerotomes into definitive vertebrae is complicated, and it is fairly common to have two successive vertebrae fuse asymmetrically or have half a vertebra missing, a cause of ___ [lateral curving of the spine]
scoliosis
the number of vertebrae is frequently more or less than the norm. In ___, the cervical vertebrae are fused causing reduced mobility and a short neck
Klippel-Feil sequence
A more severe abnormality is ___, in which the neural tube fails to close, vertebral arches fail to form, and neural tissue is exposed
spina bifida cystica
One of the most serious vertebral defects is the result of imperfect fusion or nonunion of the vertebral arches. Such an abnormality, known as ___ [___], may involve only the bony vertebral arches, leaving the spinal cord intact.
cleft vertebra [spina bifida]
the bony defect is covered by skin, and no neurological deficits occur [___]
spina bifida occulta
Costal cartilages are formed by sclerotome cells that migrate across the ___ into the adjacent lateral plate mesoderm
lateral somitic frontier
___ occur in approximately 1% of the population and are usually attached to the seventh cervical vertebra. Because of its location, this type of rib may impinge on the brachial plexus or the subclavian artery, resulting in varying degrees of anesthesia in the limb
Cervical ribs
___ is a very rare defect and may be complete or located at either end of the sternum. Thoracic organs are covered only by skin and soft tissue. The defect arises when the sternal bands fail to grow together in the midline
Cleft sternum
___ is the term for a depressed sternum that is sunken posteriorly
Pectus excavatum
___ refers to a flattening of the chest bilaterally with an anteriorly projecting sternum. The projection of the sternum resembles the keel of a boat.
Pectus carinatum
Craniosynostosis, broad great toes and thumbs, Cloverleaf skull, underdeveloped face
Pfeiffer syndrome
Gene and chromosome of Pfeiffer syndrome
FGFRl -8p12
Gene and chromosome of Pfeiffer syndrome, Apert syndrome, Jackson-weiss syndrome, and crouzon syndrome
FGFR2 - 10q26
Craniosynostosis, underdeveloped face, symmetric syndactyly of hands and feet
Apert syndrome
Craniosynostosis, underdeveloped face, foot anomalies, hands usually spared
Jackson—Weiss
syndrome
Craniosynostosis, underdeveloped face, no foot or hand defects
Crouzon syndrome
Short—limb dwarfism, underdeveloped face
Achondroplasia [ACH]
Curved short femurs, with or without cloverleaf skull
Thanatophoric
dysplasia [type I]
Relatively long femurs, severe cloverleaf skull
Thanatophoric
dysplasia [type II]
Milder form of ACH with normal craniofacial features
Hypochondroplasia
Craniosynostosis, midfacial hypoplasia, cleft palate, vertebral anomalies, hand and foot abnormalities
Saethre—Chotzen
syndrome
Small, short digits, divided uterus, hypospadias
Hand—foot—genital
syndrome
Fused, multiple digits
Synpolydactyly
Digit defects, absent radius, limb bone hypoplasia, atrial and ventricular septal defects, conduction abnormalities
Upper limb and heart
defects
Shortening, bowing, and hypomineralization of the long bones, blue sclera
Limb defects, blue
sclera
Long limbs and face, sternal defects [pectus excavatum and carinatum], dilation and dissection of the ascending aorta, lens dislocation
Marfan syndrome
