Skeletal system Flashcards
When do the notochord and the neural tube form
3rd week
As the notochord and neural tube form int he third week, the __ ___ lateral to these structures thickens to form two longitudinal columns of ___ ___
Intraembryonic mesoderm
Paraxial mesoderm
Toward the end of the third week, these columns located in the trunk, become segmented into blocks of mesoderm-__
Somites
Externally he somites appear as a bead like elevations along the dorsolateral surface of the embryo. Each somite differentiate into two parts:
The ventromedial part is sclerotome
The dorsolateral part is the dermomyotome
Sclerotome
Cells form the vertebrae and rise
Dermomyotome
Cells from its myotome region form myoblasts and those from its dermatome region form dermis
Cartilage develops from mesenchyme during the _ week
Fifth
In areas where cartilage is to develop, the mesenchyme condenses to form __ __
Chondrification centers
The mesenchymal cells differentiate into __, which secrete collagenous fibrils and extracellular matrix
Chrondroblasts
Subsequently, collagenous and or elastic fibers are deposited int he intercellular substance or __
Matrix
Three types of cartilage in matrix
Hyaline
Fibrocartilage
Elastic
Hyaline cartilage
Most widely distributed type in synovial joints
Fibrocartilage
IV discs
Elastic cartilage
In auricle of the external ears
Bone develops primarily in two types of CT, ___ and ___, but it can also develop in other CT(patella develops ina. Tendon)
Mesenchyme
Cartilage
Intramembranous bone formation
Flat bones develop in mesenchyme within preexisting membranous sheaths
Endochondral bone formation
Mesenchymal models of most limb bones are transformed into cartilaginous bone models, which later become ossified
Like cartilage, bone consists of cells and an organic intercellular substance-__ __, which comprises collagen fibrils embedded in an amorphous component
Bone matrix
Osteogenesis and chondrogenesis are programmed early in development , and are independent processes under the influence of ____ ___
Vascular events
What signaling molecules have been implicated as endogenous regulators of chondrogenesis and skeletal development
The hox genes, bmp 5, 7 and growth differentiation factors 5-members of the tgfb superfamily
In intramembranous ossification, the mesenchyme condenses and becomes highly ___; some cells differentiate into ____ and begin to deposit unmineralized matrix-__ ___
Vascular
Osteoblasts
Osteoid
__ signaling is a key factor in osteoblast differentiation
Wnt
__ __ is then deposited in osteoid tissue as it is organized into bone
Calcium phosphate
Osteoblasts are trapped in the matrix and become ___
Osteocytes
Spicules of bone soon become organized and coalesce into ____
Lamellae (layers)
Concentric lamellae develop around blood vessels, forming ____
Osteons (haversian systems)
Some osteoblasts remain at the periphery of the bone and continue to lay down lamellae, forming plates of compact bone on the surfaces
Ok
Between the surface plates, the intervening bone remains speculated, or spongy
This spongy environment is somewhat accentuated by the action of osteoclasts that reabsorb bone
In the interstices of the spongy bone, the mesenchyme differentiates into __ ___
Bone marrow
During fetal and postnatal life, continuous remodeling of bone occurs by the coordinated action of __ and ___
Osteoclasts and osteoblasts
What is endochondral ossification
Cartilaginous bone formation
Type of bone formation that occurs in preexisting cartilaginous models
In a long bone, the primary center of occification appears in the ___, which forms the shaft of a bone
Diaphysis
In the primary ossification center, the cartilage cells increase in size (hypertrophy), the matrix becomes calcified, and the cells die
Concurrently a thin layer of bone is deposited under the perichondrium surrounding the siaphysis; thus the perichondrium becomes the periosteum
The perichondrium becomes the ___
Periosteum
Invasion of the vascular connective tissue by the blood vessels surrounding the periosteum breaks up the cartilage
Ok
Some invading progenitor cells differentiates into ___ ___. This process continues toward the epiphyses (end of the bones)
Hematopoietic cells (blood cells of the bone marrow
The spicules (small needle-shaped body) of bone are remodeled by action of the osteoclasts and osteoblasts
Osteoclasts osteoblasts
Lengthening of the long occurs at diaphysis epiphyseal junction
The lengthening of bone depends on the epiphyseal cartilage plates, whose chondrogenesis proliferate and particulate in endochondral bone formation
Toward the diaphysis, the cartilage cells increase in size and the matrix becomes ___
Calcified
The spicules are isolated from each other by vascular invasion from the marrow of ___ __ ) __ ___
Medullary cavity of long bone
Bone is deposited on these spicules by osteoblasts;resorption of this bone keeps the spongy bone masses relatively constant in length and enlarges the medullary cavity
Ok
Rickets is a disease in children attributable to __ ___ _
Vitamin d defiency
Vitamin D is required for __ absorption in the intestine
Calcium
A calcium defiency(related or unrelated to vitamin D) causes disturbances in ossification of the epiphyseal cartilage plates and there is disorientation of cells at the metaphysis. What is the metaphysis
Flared part of diaphysis nearest the epiphysis
What do limbs look like with rickets
Shortened and deformed, with severe bowing of the limb bones
Rickets may also delay closure of ____ of the cranial bones in infants
Fontanelles
Ossification of limb bones begins at the end of the embryonic period (56 days after fertilization). Therefore, when are there demands on the maternal supply of calcium and phosphorus
8 weeks
At birth, the diaphyses are largely ___ but most of the epiphyses are still ____
Ossified
Cartilaginous
When do secondary ossification centers appear in the epiphyses
First few years after birth
The epiphyseal cartilage cells hypertrophy and there is invasion by vascular CT
Ok
Ossification spreads rapidly and only articular cartilage and epiphyseal cartilage plat remain ___
Cartilaginous
Upon completion of growth the cartilage plate is replaced by spongy bone; the epiphyses and diaphyses are united and no further elongation of the bone occurs
Ok
In most bones , the epiphyses have fused with the diaphysis by the age of ___
20
Growth in the diameter of a bone results from deposition of bone at the ___ and from resorption on the internal medullary surface
Periosteum
The rate of deposition and resorption is balanced to regulate the thickness of compact bone and the size of the medullary cavity.
The internal reorganization of bone continues throughout life
Joints begin to develop with the appearance of __ ___ during the 6th week and by the end of the __ week they resemble adult bones
Condensed mesenchyme
8th
During the development of fibrous joints, the ___ ___ between the developing bones differentiates into dense fibrous tissue
Interzonal mesenchyme
Give an example of a fibrous joint
Sutures of the cranium
During development of the cartilaginous joints, the interzonal mesenchyme between the developing bones differentiates into __ __ or ____
Hyaline cartilage
Fibrocartilage
During development of synovial joints, the interzonal mesenchyme between the developing bones differentiates as follows:
Peripherally, the interzonal mesenchyme forms the joint capsular ligament and other ligaments
Centrally, the mesenchyme disappears and the resulting space becomes the joint cavity or synovial cavity
Where the mesenchyme lines the joint capsule and articular surfaces it forms the synovial membrane which secretes synovial fluid
What is the axial skeleton
Cranium, vertebral column, ribs , sternum
Some densely packed cells move cranial, opposite the center of the myotome, where they form the ___ _. What do these cells express
IV discs
PAX1, a paired box gene
The remaining densely packed cells fuse with the loosely arranged cells of the immediately caudal sclerotome to form the mesenchymal ___, the primordium of a body of a vertebra
Centrum
Thus, each centrum develops from two adjacent sclerotome and becomes an intersegmental structure
The spinal nerves now lie in a close relationship with the IV discs, and the intersegmental arteries lie on each side of the vertebral bodies
In the thorax, the dorsal intersegmental arteries become the intercostal arteries
Ok
Studies indicate that the regional development of the vertebral column is regulated along the anterior posterior axis by what
HOX AND PAX
WHERE IT IS SURROUNDED BY THE DEVELOPING VERTEBRAL BODIES, THE NOTOCHORD DEGENERATES ANDN DISAPPEARS.WHAT HAPPENS BETWEEN THE VERTEBRAE
The notochord expands to form the gelatinous center of the IV disc-the nucleus pulposus
The nucleus is later surrounded by circulatory arranged fibers that form the ___ ___
Annulus fibrosus
The nucleus pulposus and anulus fibrosus together constitute the ___ __
IV disc
The mesenchymal cells that surround the neural tube form the ___ __, the primordium of the ___ ___
Neural arch
Vertebral arch
The mesenchymal cells in the body wall form the __ __, which form the ribs in the thoracic region
Costal processes
Remnants of the notochord may persist and form a ___, a rare neoplasm
Chordoma
Approximately 1/3 of these slowly growing chordoma, malignant tumors occur at the base of the cranium and extend to the ____
Nasopharyx
Chordoma infiltrate bone and are difficult to remove
They also develop in the lumbosacral region. Surgical resection has provided long term disease free survival for many people
During the _ week, chondrification centers appear in each mesenchymal vertebra
6th
At the end of the embryonic period the two centers in each __ fuse to form a cartilaginous centrum
Centrum
Concomitantly, the centers in the neural arches fuse with each other and the centrum
The spinous and transverse processes develop from extensions of the chondrification centers in the neural arch
___ spreads until a cartilaginous vertebral column is formed
Chondrification
Ossification of typical vertebrae begins during the embryonic period and usually ends by the __ years
25th
There are two primary ossification centers in the centrum, the __ and ___, which soon fuse to form one another
Dorsal ventral
Three primary centers are present by the _ week: one in the centrum and one in each half of the neural arch
8th
Ossification becomes evident in the neural arches during the __ week
8th
Ossification becomes evident in the neural arches during the _ week
8
At birth each vertebra consists of three bony parts connected by ___
Cartilage
The bony halves of the vertebral arch usually fuse during the first - years
3-5
The arches first unite in the lumbar region and union progresses cranially
The vertebral arch articulates with the centrum at cartilaginous neurocentral joints, which permit the vertebral arches to grow as the spinal cord enlarges
The neurocentral joints disappear when
When the vertebral arches fuse with the centrum during the 3rd to 6th years
What are the five ossification centers that appear in the vertebrae after puberty
One for the tip of the spinous process
One for the tip of each transverse process
Two anular epiphyses, one on the superior rim and one on the inferior rim of the vertebral body
The __ __ is a composite of the anular epiphyses and the mass of bone between them
Vertebral body
All secondary centers unite with the rest of the vertebrae at __ years of age
25
Where are there variations in the ossification of vertebrae
C1, c2, c7 vertebrae , and in lumbar vertebrae , sacrum and coccyx
Most people have _ cervical, _ thoracic, _ lumbar, and _ sacral vertebrae
7, 12, 5, 5
An apparent extra (or absent) vertebra in one segment of the column may be compensated for by an absent (or extra) vertebra in an adjacent segment
Ok
Klippel-feel syndrome(brevicollis) features
Short neck, low hairline, restricted neck movements, fusion of vertical vertebral bodies, abnormalities of brainstem and cerebellum
In most cases , the number of cervical vertebral bodies is fewer than normal due to fusion of vertebrae before birth
In some cases, there is a lack of segmentation of several elements of the cervical region of the vertebral column
The number of cervical nerve roots may be normal but they are small, as are the IV foramina.
Persons with this syndrome may have other birth defects, including scoliosis and urinary tract disorders
What do ribs develop from
Mesenchymal costal processes of the thoracic vertebrae
The ribs become __ during the embryonic period and ___ during the fetal period
Cartilaginous
Ossify
What is the original site of union of the costal processes with the vertebrae replaced by
Costovertebral synovial joints
True ribs
1-7 attach by their own cartilages to the sternum
False fibs
8-12 attach to their sternum trough the cartilage of another rib or ribs
Floating ribs
The last two pairs of ribs 11, 12 do not attach to the sternum
In development of the sternum, A pair of vertical mesenchymal bands-__ __-develop ventrolaterally in the body wall
Sternal bars
___ occurs in sternal bars as they move medially
Chondrification (converion into cartilage)
Sternal bars fuse craniocaudlaly in the median plane to form cartilaginous models of the ___, ___, and ____ ___
Manubrium, sternebrae, and xiphoid process
Sternum: centers of ossification appear ____ in the sternum before birth, except the ossification center of the ___ __, which appears during ___
Craniocaudally
Xiphoid process
Childhood
The xiphoid may never completely ___
Ossify
The cranium develops from ___ surrounding the developing brain
Mesenchyme
Neurocranium
Bones of the cranium enclosing the brain
Viscerocranium
The bones of the facial skeleton derived from the pharyngeal arches
__ ___ of the neurocranium forms the bones of the base of the cranium
Endochondral ossification
The ossification pattern of the neurocranium has a definite sequence. What is it
Occipital first, ten sphenoid, then ethmoid
The __ __, or __ __ forms around the cranial end of the notochord and fuses with the cartilages derived from the sclerotome regions of the occipital somites
Parachordal cartilage or basal plate
The parachordal cartilage or basal plate, contributes to the ___ of the occipital bone; later, extensions grow around the cranial end of the spinal cord and form the boundaries of the __ ___
Base
Foramen magnum
What is the foramen magnum
Large opening int he basal part of the occipital bone
The __ __ forms around the developing pituitary gland and fuses to form the body of the sphenoid bone
Hypophysial cartilage
The __ __ fuse to form the body of the ethmoid bone
Trabeculae cranial
The __ __ forms the lesser wing of the sphenoid bone
Ala orbitalis
Otic capsules envelop around the otic vesicles, the primordia of the __ __, and form the __ and __ parts of the temporal bone
Internal earths
Petrous, mastoid
Nasal capsules develop around the nasal sacs and contribute to the formation of the __ __
Ethmoid bone
Membranous ossification occurs in the head mesenchyme at the sides and top of the brain, forming the ___
Calvaria
During fetal like , the flat bones of the calvaria are separated by dense CT membranes that form fibrous joints-the ___ of the calvaria
Sutures
Six large areas __, are present where several sutures meet
Fontanelles
The softness of the bones and their loose connections at the sutures enable the calvaria to undergo changes of a shape during birth (___ of fetal cranium)
Molding
During birth, The frontal bones become __, the occipital bone is __ __ and one parietal bone slightly overrides the other one
Flat
Drawn out
After birth when does the shape of the calvaria return to normal
Few days
The cartilaginous viscerocranium is derived fromt he cartilaginous skeleton of the first __ pairs of pharyngeal archess
2
The dorsal end of the first pharyngeal arch cartilage forms the __ and __ of the middle ear
Malleus incus
The dorsal end of the second pharyngeal arch cartilage forms a portion of the __ of the middle ear and __ process of the temporal bone.
Stapes
Styloid
The ventral end of the second pharyngeal arch ossifies to form the __ __ of the ___ ___
Lesser bone
Hyoid bone
The third, fourth, and sixth pharyngeal arch cartilages for only in the ___ parts of the arches.
Ventral
The third arch cartilages form the __ __ of the ___ ___
Greater horns
Hyoid bone.
The fourth and sixth pharyngeal arch cartilages fuse to form the ___ cartilages except for the ____
Laryngeal
Epiglottis
___ ossification occurs in the maxillary prominence of the first pharyngeal arch and subsequently forms the squamous temporal, maxillary and zygomatic bones
Membranous
The squamous temporal bones become part of the ____
Neurocranium
The mandibular prominence forms the ___
Mandible
Some __ ossification occurs int he median plane of the chin and in the mandibular condyle
Endochondral
The cranium of a neonate is __ in proportion to the rest of the skeleton, and the face is __ compared with the calvaria
Large
Small
Why is the face small on a newborn
Small size of jaws, absence of Paranasal sinuses and underdevelopment of hte facial bones
After recovering from molding, the neonates cranium is ___ and its bones are __
Round
Thin
The _ __ permit the brain and calvaria to enlarge during infancy and childhood.
Fibrous sutures
When is the increase in size the greatest for the postnatal cranium and why
First two years . The period of most rapid growth of the brain
The calvaria continues to expand to conform to brain growth until _ years, after which its size usually increases slightly for 3-4 years bc of thickening of its bones
16
There is also rapid growth of the face and jaws, coinciding with eruption of the primary (___) teeth
Deciduous
Facial changes are more marked after secondary (__) teeth erupt
Secondary
There is concurrent enlargement of the frontal and facial regions , associated with the increase in the size of the ___ ___
Paranasal sinuses (maxillary sinuses
what is growth of the Paranasal sinuses important for
Resonance to the voice
Accessory ribs, usually rudimentary, result from the development of costal processes from the __ or __ vertebrae
Cervical
Lumbar
The most common accessory rib is a ___ rib ,but it is clinically ___
Lumbar
Insignificant
A cervical rib occurs in -% of people and os often fused with the _ rib
.5-1
1st
A cervical rib is usually attached to the __ of the sternum or the _ cervical vertebrae
Manubrium
7th
Why would a cervical rib produce neurovascular symptoms
Pressure of a cervical rib on the brachial plexus of nerves, partly in the neck and axilla, or on the subclavian artery often produces neurovascular symptoms (paralysis and anesthesia of the upper limb
Usually developing vertebral bodies have _ chondrification centers that soon unite
2
What is a hemivertebra
Failure of one of the chondrification centers to appear and subsequent failure of half of the vertebra to form
Hemivertebra is the most common cause of __ __ or the vertebral column
Congenital scoliosis
Rachischisis
Vertebral abnormalities in a complex group of anomalies (spinal dysgraphia) that primarily affect axial structures
In neonates with rachischisis, the neural folds do not fuse, either because of faulty induction by the underlying notochord or bc of a teratogenic agent
Ok
Acrania
The neurocranium is absent and there are major birth defects of the vertebral column that are incompatible with life
Acrania is associated with ____ and ____
Meroencephaly
Rachischisis
What is meroencephaly
Partial absence of the brain
What is rachischisis
Extensive clefts in the vertebral arches of the vertebral column
When does meroencephaly occur
Cranial end of the neural tube does not close during the 4th week of development, resulting in subsequent failure of the calvaria
Craniosynostosis
Several birth defects result from prenatal fusion of the cranial sutures
Cause of craniosyntosis
Unclear but genetic factors appear to be important. HOX(MSX2 and ALX4) mutations have been implicated in cases
Craniosyntosis is more common in ___ and often associated with what
Males
Other skeletal defects
The type of cranial deformation produced in craniosyntosis depends on what
Which sutures close prematurely
Scaphocephaly
Sagittal suture closes first
Cranium elongated and wedge shaped
Most common craniosynostosis
Scaphocephaly
Brachycephaly
Premature closure of the coronal suture
High , tower like cranium
Plagiocephaly
Coronal suture closes prematurely on one side only
Cranium twisted and asymmetrical
Trigonocephaly
Premature closure of the frontal (metopic) suture results in a defect of the frontal bone and other defects
What is the appendicular skeleton
Pectoral and pelvic girdles and limb bones
During the _ week the mesenchymal bone models in the limb undergo chondrification to form ___ cartilage bone models
Hyaline
The clavicle initially develops by __ ___ and it later forms growth cartilages at both ends
Intramembranous ossification
The models of the pectoral girdle and uppper limb bones appear slightly before those of the pelvic girdle and lower limb bones
The bone models appear in a proximodistal sequence
The moleculcular mechanism of limb morphogenetic is regulated by specialized signaling centers along three axes of development . Patterning in the developing limbs is controlled by ___ and other complex signaling pathways
HOX
Ossification begins in the long bones by the __ week
8th
By _ weeks, primary ossification centers have appeared in nearly all limb bones
12
The ___ begin to ossify before any other bones in the body, followed by __
Clavicle
Femurs
Virtually all primary centers of ossification are present at birth
Diaphyseal
The centers for the distal end of the femur and the proximal end of the tibia usually appear when
Last month of intrauterine life (34-38 weeks)
The centers of the other bones appear after birth
Ok
The part of the bone ossified from the secondary center is the _—
Epiphysis
The bone formed fromt he primary center in the diaphysis does not fuse at the epiphyseal cartilage plate with that formed fromt he secondary centers in the epiphysis until the bone grows to its adult length
This delay enables lengthening of the bone to continue until the final size is reached
A radiologist can determine bone age by assessing the ossification centers using two criteria
The time of appearance of calcified material in the diaphysis, epiphysis or both is specific for each diaphysis and epiphysis and for each bone and sex
The disappearance of the dark line representing the epiphyseal cartilage plate indicates that te epiphysis has fused with the diaphysis
Fusion of the diaphyseal-epiphyseal centers , which occurs at specific times for each ap I physics, happens 1-2 years earlier in __ than ___
Females
Males
__ is the most common cause of dwarfism
Achondroplasia
1/15000
In achondroplasia, the limbs become bowed and short. Why
A disturbance of endochondral ossification at the epiphyseal cartilage plates, particularly of the long bones, during fetal life
What do babies with achondroplasia look like
Trunk is short and head is enlarged with a bulging forehead and a scooped out nose (flat nasal bone)
Inheritance pattern of achondroplasia
AD, 80% can arise from new mutations-rate increases with paternal age
The majority of achondroplasia is due to a point mutation in ____
F.1,11,12 in the FGFR3 gene
What does f.1,11,12 in the FGFR3 gene do with a point mutation
Magnification of the normal inhibiting effect of endochondral ossification, specifically int he zone of chondrocyte proliferation
-shortened bones,but does not affect growth of bone width(periosteal growth)
Congenital infantile hyperpituitarism
Causes abnormally rapid growth in infancy
Rare
What does congenital infantile hyperpituitarism result in
Gigantism
In adults, hyperpituitarism results in ___
Acromegaly
In acromegaly, the epiphyseal and siaphyseal centers of the long bones fuse, thereby preventing ___ of the bones
Elongation
Both gigantism and acroemegaly result from an excessive secretion of __ __
Growth hormone
Acromegaly is in _ and gigantism i sin _
Adults
Kids
