Final Exam Flashcards
When does the skeletal system of the embryo begin to form?
At the end of the 4th week of development
Somites divide into what two parts?
Dermomyotome (dermatome and myotome) and Slcerotome
The skeletal system begins development with what part of the somites?
The ventral medial somite.
Somites develop specifically from what embryonic layer?
Paraxial mesoderm
In general, what embryonic layer gives rise to the skeletal system?
Mesoderm
The dividing somite is made up of mesodermal cells, which give rise to what?
Mesenchyme
This structure is a meshwork of loosely organized embryonic connective tissue. Bone and cartilage develop from it.
Mesenchyme
What are the two types of cartilage bone development?
Intercartilagenous and endochondral ossification
The cartilage stage in bones can grow rapidly to match what?
The growth of the fetus
When does cartilage begin to form?
The middle of the 5th week
These are mesenchymal cells that proliferate, enlarge, and become round. They also produce collagenous fibers and matrix.
Chondroblasts
Chondroblasts form what type of centers?
Chondrification centers
What does internal growth of cartilage result from?
Division of cartilage cells and from the production of matrix
The growth of cartilage follows the growth of what other type of tissue?
Bone tissue
During what week of development do mesenchyme cells condense to form chondrification centers?
8th week
What type of cells lay down new bone tissue?
Osteoblasts
When osteoblasts become trapped within bone tissue what type of cells do they develop into?
Osteocytes
Condensation of mesenchyme will give rise to what?
The formation of bone models
Describe intramembranous ossification?
- Mesenchyme condenses and vascularizes
- Cells differentiate into-osteoblasts, which deposit osteoid tissue to form ossification centers
- Bone matrix is deposited to form lamellae, which develop around blood vessels to form osteons
- The lamellae then grows and thickens to become trabeculae
What are the two types of development for the skull?
Neurocranium and splanchinocranium
Where does the neurocranium develop from?
The mesenchyme surrounding the brain
What are the two types of neurocranium development?
Neurochondrocranium and neuromembranocranium
This type of neurocranium development involves the cartilaginous base of the neurocranium and the skull and is followed by endochondral ossification, which begins around 8 weeks.
Neurochondrocranium
This type of neurocranium development involves the sides and the roof of the neurocranium and is formed by intramembranous ossification.
Neuromembranocranium
During fetal life, bones are separated by connective tissue membranes known as what?
Sutures
At the angle of bones within the skull of the developing fetus, large fibrous areas are formed. The membranes covering these spaces are known as what?
Fontanelles
What are the names of the fontanelles of a developing child?
Anterior, posterior, anterolateral, and posterolateral fontanelles
When does the anterior fontanelle close?
It closes by the end of the second year.
What is the largest fontanelle in a developing child?
Anterior fontanelle
When does the anterolateral fontanelle close?
At two to three months
When does the posterolateral fontanelle close?
At the end of the first year
Due to the softness, fontanelles and sutures of the fetal skull what can undergo changes during the birth process?
Calvaria or skull cap
This type of splanchnocranium undergoes endochondral ossification and is composed of replacing bone.
Splanchnochondrocranium
The cartilaginous skeleton develops from what?
Visceral, pharyngeal, or branchial arches
How many visceral, pharyngeal, or branchial arches do humans have?
We start with 6 but the 5th disappears in 1.5 days.
What does the first visceral arch form?
Palate, maxilla, meckel’s cartilage, incus, and malleus. Muscles of mastication
What does the second visceral arch form?
Stapes, cranial half of the hyoid, and lesser horn. Facial muscles
What does the third visceral arch form?
The caudal half of the hyoid and the greater horn. Stylo-pharyngeal muscle
What do the 4th and 6th visceral arches form?
Cartilages of the larynx. No ossification occurs here. Laryngeal muscles, pharyngeal muscles, palate muscles, part of the SCM, and part of the trapezius
The vertebral column develops from what?
Somite mesenchyme sclerotome
When does chondrification of the vertebrae occur?
7th week in the cranial vertebrae and follows to lower levels
Vertebral arches do not unite to form spinous processes until what time?
The 3rd month after birth
When does ossification of the vertebrae occur?
Begins at 9 weeks
How many ossification centers are there in the vertebrae? Where are they located?
There are three. One in the centrum and one in each half of the vertebral arch
How many ossification centers are present on the vertebrae during puberty? Where are they located?
There are 5. One at the tip of the spinous process, one at each tip of the transverse process, and two on the rim of the epiphyseal center
Where do the ribs develop from?
The mesenchyme and cartilage of the costal processes
How many ossification centers does each rib have? When does ossification occur?
One. Occurs in the 9th week
This bone begins as intramembranous bone, develops growth cartilages at both ends, and ossifies before any other bone.
Clavicle
This condition is more commonly known as dwarfism, autosomal dominant, and is characterized by slow growth of cartilage and bone ossification resulting in a small stature, megalocephaly (large face, head), and skeletal issues.
Achondroplasia syndrome
This is a mild form of achondroplasia characterized by small stature and short bowed limbs/lumbar lordosis.
Hypochondroplasia syndrome
This condition is characterized by the storage of lipids in the nervous system and an accumulation of mucopolysaccharides in the mesenchyme.
Mucopolysaccaridosis (Hurlers and Hunters)
This condition is characterized by clavicle agenesis, skull disorders, and jaw disorders.
Cleidocranial dysostosis
This type of spina bifida is limited to the skeletal components.
Occulta
This type of spina bifida occurs in the meninges (meningocoele) and the meninges and spinal cord (meningomyelocoele).
Cystica
This condition is characterized by abnormal curvature of the spine (numerical variations, morphological variations, or both)
Congenital scoliosis
This condition is characterized by the lack of ossification of the skull at the time of birth.
Cranial dysostosis
This is characterized by a premature closure of the sutures of the skull.
Craniostenosis
This condition is characterized by all of the sutures closing prematurely and symmetrically.
Oxycephaly
This condition is characterized by all of the sutures closing asymmetrically.
Plagiocephaly
This condition is characterized by the sagittal sutures closing prematurely.
Scaphocephaly
This condition is characterized by the coronal suture closing prematurely.
Acrocephaly (brachycephaly)
This condition is characterized by acrocephaly (premature closure of the coronal sutures) and syndactyly (fusion of the digits).
Aperts
This condition characterized by scaphocephaly (premature closure of the sagittal sutures) and no syndactyly (fusion of the digits)
Crouson’s
This condition is characterized by a complete absence of limbs and is most often caused by environmental factors
Amelia
This condition is characterized by an absence or reduction of the proximal part of the limbs and is most often caused by environmental factors.
Phocomelia
This condition is characterized by an absence or reduction of the distal part of the limbs and is most often caused by environmental factors.
Meromelia
This condition is characterized by hypoplasia and fusion of the lower limbs and occurs spontaneously.
Sympodia (monopodia)
This condition is characterized by a duplication of the distal parts of the limbs and is autosomal dominant.
Dichiria