Skeletal System Flashcards
The 4 portions of the skeletal system:
vertebrae, ribs, skull, and limbs
Skeletal system develops from which 2 cell layers?
Ectoderm and mesoderm
Overview of bone and cartilage development: induction of neural crest is the interaction between ______ and _____ with signal emanating from the ectoderm and received by the _________, although some bidirectional signaling does occur.
The neural plate; ectoderm; neuroepithelium
In the head and neck, mesoderm and neural crest cells contribute to _________ (embryonic connective tissue). This produces many cell types including:
Mesenchym; fibroblasts, osteoblasts, and chondroblasts
2 principle ways of producing bone:
Intramembranous and endochondral
Type of bone formation that is formed directly in a condensation of mesenchyme:
Intramembranous bone formation (flat bones)
Type of bone formation in which a cartilage model condenses from mesenchyme first, then is replaced by bone:
Endochondral bone formation (limbs)
Somites form from the ________ in a segmental manner.
Paraxial
The _____ portion of the somite forms the sclerotome which surrounds the ______ and ______.
Ventral; neural tube; notochord
The sclerotome is induced by the neural tube to produce:
Vertebrae and intervertebral discs.
Mesenchyme, which is embryonic connective tissue, is largely _______ with some neural cell contribution.
Mesoderm (fibroblasts, osteoblasts, and chondroblasts)
Somites form during the ___ week of gestation and are visible through the ________ ectoderm.
3rd; surface
Somites establish segmental organization. The first 4 pairs from in the _______ region and contribute to what?
Occipital - contribute to development of occipital region of the skull, the bones that form around the nose, eyes, and inner ears
The next 8 pairs form in the _______ region and contribute to:
Cervical; contribute to occipital bone and others form the cervical vertebrae
The next 12 pairs form the _______ region and contribute to:
Thoracic; contribute to the thoracic vertebrae and bones of the thoracic wall
The rest of the somites:
5 lumbar, 5 sacral, 3 coccygeal somites. There are 42-44 pairs of somites that form with 3-4 forming/day
The sclerotome surrounding the neural tube forms the:
Vertebral arch
The sclerotome surrounding the notochord forms the:
Centrum (primordium of the body) of the vertebrae and the intervertebral discs
The ventral portion of sclerotome cells surround the:
Notochord (and form vertebral bodies)
The dorsal portion of sclerotome cells surround the:
Neural tube (and form vertebral arches)
In the body wall, sclerotome cells form:
Costal processes which form ribs in the thoracic region
______ is the exclusive material for the vertebral column.
Sclerotome
What is the role of the sonic hedgehog gene (shh)?
From the notochord and floor plate of the neural tube, signals sclerotomal differentiation and ventral migration from the somite.
What is the role of the bone morphogenetic protein (bmp)?
It is expressed by the roof plate and Wnt signalling from the ectoderm induces dermomyotome differentation
Each sclerotome is initially located segmentally but:
It forms intervertebral space for segmental spinal nerve to innervate appropriate myotome
Cells in the caudal portion of the sclerotome fuse with rostrally located cells of caudal neighboring sclerotome to form:
Centrum of vertebrae (primordium of body). The notochord in this region degenerates ***
What happens with formation of vertebrae from caudal portion of one sclerotome and cranial portion of the neighbor:
- Causes the vertebrae to be located intersegmentally
2. Places intervertebral space to allow segmental spinal nerve to grow directly to innervate the appropriate myotome
Arteries, which are first intersegmental, now lie:
On each sides of vertebral bodies
The sclerotome cells in the middle (opposite each myotome) surround the notochord to form the:
Annulus fibrosus of the intervertebral disc. The notochord in this region forms the nucleus pulposis
Mesenchyme continues to surround the spinal cord to form:
Vertebral arches
Mesenchyme condenses in body wall to form:
Costal processes, which form ribs
Cervical region development: the first 8 somites give rise to the 7 cervical vertebrae because:
The upper half of the first sclerotome contributes to the formation of the occipital bone. The caudal portion of the 8th cervical scelrotome contributes to T1 (7 cervical vertebrae, 8 cervical nerves)
What is derived from a single somite?
Neural arch
What receives contributions from two adjacent somites?
Vertebral body
What forms in the mesenchyme in the 6th week?
Cartilage
What begins in 7-8 weeks and continues for ~25 years?
Ossification of caritlage
At the end of the embryonic period, there are:
3 primary ossification centers
What are the 3 primary ossification centers at the end of the embryonic period?
Centrum and each half of the vertebral arch
At birth, there are bony pieces connected by cartilaginous “joints” to allow for expansion of the spinal cord during growth between:
The arch and centrum (2) and between halves of the vertebral arch
During the postnatal period:
The arches fuse to centrum by 3-6 years
In puberty, the secondary ossification centers are present and they form:
Tip of spinous processes and transverse process, and annulus epiphysis of body
Spina bifida:
Spina bifida occulta and spina bifida cystica. It is the failure of fusion of vertebral arch around the spinal cord. The involvement of spinal cord ranges from insignificant to severe. ***This can be prevented with folic acid supplementation
Spina bifida occulta:
The most common, site is covered by skin and marked by a tuft of hair, may be insignificant but is prone to trauma
Spina bifida cystica:
Involves herniation of meninges and/or spinal cord through defect in the vertebral arch. It is covered by skin or a thin membrane and may occur anywhere but is most common in the lumbar region (menigocele, meningomyelocele, rachischisis)
SB cystica - meningocele:
Protrusion of meninges and CSF but NOT the spinal cord, repaired surgically
SB cystica - meningomyelocele:
Protrusion of spinal cord and meninges into cyst. Symptoms/loss of function depends on location - usually lumbar
SB cystica - Rachichisis:
Series of wide open vertebrae often associated with an open neural tube (myeloschisis). Results from the failure of neural folds to close. AKA large meningomyelocoele
Hemivertebra:
Failure of one chondrification center to appear in centrum, producing only half a vertebral body - causes scoliosis
Which of the following structures is not derived from the sclerotome portion of the somite? A. vertebral body B. vertebral arch C. sacrum D. notochord
Notochord
Failure to fuse by which of the following structures leads to spina bifida occulta? A. neural folds B. neural arch processes C. vertebral bodies D. neural plates
Neural arch processes
Which of the following is true about spina bifida occulta?
A. It leads to immediate death
B. It is usually found in the cervical region of the vertebral column
C. It usually produces no clinical symptoms
D. It involves the vertebral arch, meninges, and nerve tissue
It usually produces no clinical symptoms
Ribs form by:
Endochondral ossification, only in the thoracic region (distal tips of the costal processes lengthen to form ribs) It grows laterally and ventrally to form all 12 thoracic ribs
Ribs join with:
Vertebrae to form the costovertebral joint
The sternum is a midline fusion of a pair of longitudinal mesenchymal condensations, ______, that form in the ventrolateral body wall. Failure of these bars to fuse may result in:
Sternal bars; cleft sternum
Accessory ribs:
Inappropriate appearance of costal process in cervical or lumbar region. Usually asymptomatic but at the cervical level, may interfere with brachial plexus or subclavian artery
When the sternal end of the rib is cleaved into two:
Bifurcated rib
Skull: the brain has an inductive influence on skull formation from the surrounding:
Mesenchyme
The components of the skull are:
Neurocranium and viscerocranium. Both have membranous parts formed by intramembranous ossification and cartilaginous parts formed by endochondral ossification
The neurocranium:
Is a protective case for the brain
The viscerocranium:
Is the skeleton of the face (neural crest cells)
The membranous neurocranium forms:
Flat bones of the calvarium (frontal, parietal, and squamous part of temporal and occipital bones) It is bridged by dense CT (sutures) to allow molding of the skull around the growing brain
There are six large membranes where sutures meet:
Fontanelles: anterior, posterior, anterolateral (sphenoidal), posterolateral (mastoid)
Fontanelles are closed by:
The end of 2nd postnatal year and sutures ossify in adulthood
Cartilaginous neurocranium (chondrocranium):
base of skull is formed by the fusion of cartilages
Viscerocranium (skeleton of face):
Membranous viscerocranium and cartilaginous vescerocranium - derived from pharyngeal arch cartilage
The neural crest cells form:
Majority of the facial and cranial skeleton, 1st 4 somites, paraxial mesodermal cells, and also contribute to facial and cranial skeleton
Cranial formation defects:
Meningocele, meningoencephalocele, meningohydroencephalocele
Cranial meningocele:
Meninges herniate through an opening in the skull
Meningoencephalocele:
Brain tissue and meninges herniate through the defect
Meningohydroencephalocele:
Meninges, brain, and portion of ventricle herniate through defect
Acrania:
Failure of calvaria and prosencephalon (anencephaly or meroanencephaly) to form. It is the most common anomaly in stillborn infants and is thought to be due to failure of rostral neuropore to close, infants usually die within a few hours, may be diagnosed using ultrasound, fetoscopy, or radiography. Elevated alphafetoprotein in amniotic fluid and polyhydramnios - fetus may lack neural control to swallow amniotic fluid
Craniosynostosis:
Premature closure of skull sutures producing unusual shapes of the skull, defect depends on which suture is affected
Microcephaly:
Failure of brain to grow may reduce growth of skull via the inductive interaction
Limb development: Limb buds appear during:
4th week, upper precedes lower by about 2 days
Cells from the somatic layer of lateral plate mesoderm forms the:
Connective tissue and cartilage
Cells migrating from the somites form:
Limb muscles
Limb buds:
Form by endochondral ossification, cartilage replaces the mesenchyme by end of 6th week, the skeleton of the limbs is formed as a hyaline cartilage precursor ossifies
Limb differentiates according to existing embryonic regions:
Apical ectodermal ridge (AER), the Zone of polarizing activity (ZPA), and the progress zone (PZ)
AER acts as:
The organizing region for the proximodistal axis of the limb, secretes fibroblast growth factor
ZPA organizes the limb along the:
Anterior-posterios axis in part through expression of Sonic hedgehog, influenced by fibroblast growth factor and retinoic acid
Apical ectodermal ridge:
Thickened portion of the ectoderm at the tip of limb bud induces growth and differentiation of limb mesenchyme. It is found at the junction of dorsal and ventral halves of the limb bud, found in both upper and lower limbs, the integrity of the apical ectodermal ridge is essential for continued limb growth
The mesenchyme becomes specified by _______ to polarize and to produce bone primordia in the appropriate sequence.
HOX genes
Events of Signal Transduction and Limb Formation: Fibroblast growth factor is released by ____ and binds to FGF receptor (a receptor tyrosine kinase) and activates it.
AER
Receptor tyrosine kinase (RTK) then phosphorylates:
Critical proteins, which causes mesenchymal cells to release retinoic acid
Retinoic acid induces ___________ in target cells
HOX gene expression
HOX Genes:
- Contain HomeOboX domain (highly conserved)
- 39 HOX genes distributed in 4 linkage groups
- HOX genes are expressed in a topographic pattern thought to underline the patterning of the limb skeleton
Endochondral ossification of cartilage model:
Negins at the end of embryonic period, which increases demand on: Maternal calcium and phosphorus. This is the primary center in diaphysis
Hematopoietic cells colonize bony spaces to form:
Bone marrow
At birth, the center of presumptive limb bone:
Diaphysis - is ossified
The ends (epiphysis):
Remains cartilaginous
After primary ossification in diaphyses:
Blood vessels invade, deliver heatopoietic cells and colonize bony spaces to form marrow. Only immature osteoblast (OB) precursors invade fetal bone from the perichondrium. A fraction of these cells wrap around blood vessels in pericyte-like fashion
Secondary ossification centers appear in:
Epiphysis after birth. A cartilaginous plate remains between the epiphyssi and the diaphysis. This is the epiphyseal plate, length increases via the plate and stops around 20 years onld
Digital ray development:
Condense from mesenchyme and are sculpted via apoptosis, as the limb bud grows, indentations become apparent in the hand (or foot) plate. During the 7th-8th weeks, the digits of the hand become apparent. As the hand develops, webs that are present between the outgrowing digits regress by apoptosis
Limb rotation during the 6-8th week: Upper limb is ______ rotation and lower limb is ______ rotation.
Upper limb - lateral rotation
Lower limb - medial roation
Innervation of lower limbs twists into a spiral
Amelia:
Complete absence of a limb (thalidomide babies), absence of an apical ectodermal ridge
Meromelia:
Partial absence of a limb, absence of an apical ectoderm ridge
Clubfoot (talipes):
Deformity of foot involving ankle bone characterized by abnormal positioning of foot that prevents weight bearing, child tends to walk on ankle not foot
Syndactyly:
Failure of mesenchyme to break down between digital rays resulting in fusion of the digits - it may involve only skin and connective tissue (cutaneous) or may be fusion of bones (osseous)
Polydactyly:
Extra digits
Which of the following statements is not correct about limb formation?
A. The apical ectodermal ridge induces mesodermal differentiation
B. Paraxial mesoderm forms bone and ligaments of limbs
C. Cell death contributes to digit formation
D. Hindlimb buds arise after forelimb buds
B. Paraxial mesoderm forms bone and ligaments of limbs
Which describes the absence of limb development?
Amelia
Which of the following cells are precursors to the bone (humerus) in the arm? A. Neural crest cells B. Sruface ectoderm C. Paraxial mesoderm D. Lateral plate mesoderm
Later plate mesoderm
Achondroplasia:
Most common cause of dwarfism - shortness of stature, trunk is normal length but limbs are short because of disturbance in endochondral ossification at the epiphyseal plate. 1/10,000 births
Hyperpituitarism:
Excessive secretion of growth hormone causes:
Rapid and excessive growth (giganticism) or enlargement of the visceral organs, soft tissues, bones of face, hands of feet (acromegaly). In this disease, the epiphyseal and diaphyseal centers fuse, preventing further elongation of the long bones
Hypothyroidism and cretinism:
Deficiency in fetal thyroid hormone produces cretinism which is characterized by growth retardation, skeletal abnormalities, mental deficiency, auditory and neurological disorders
