11. Skeletal System Devo

Question 1

The initial progenitor tissue of all musculoskeletal (MS) tissues is

Answer 1

mesenchyme… referred to as Skeletal Tissue Forming Mesenchyme (STFM). The STFM is derived from several sources.

Question 2

Vertebrae and ribs come from

Answer 2

Scleratome tissue of the somites

Question 3

Sternum comes from

Answer 3

Somatic mesoderm of ventral body wall

Question 4

Skull comes from

Answer 4

Head mesoderm
Scleratome tissue of occipital somites,
Neural crest ectomesenchyme

Question 5

appendicular skeleton (bones of the limbs and limb girdles) is derived from

Answer 5

Somatic Mesoderm.

Question 6

What are the developmental phases for skeletal tissues?

Answer 6

The cells in skeletal precursor tissues have a mesenchyme phenotype. Once they have received inductive signals, the mesenchyme cells condense into Preskeletal Mesenchyme Condensations (PMC) sometimes called a blastema. Inductive signals for PMC are often derived from an adjacent epithelium.

Question 7

method of forming bone Directly From

Mesenchyme without a cartilage intermediate.

Answer 7

Intramembranous Ossification

Question 8

Signals, most likely from the adjacent epithelium, result in expression of____________ in the mesenchymal
cells that then differentiate into osteoblasts (bone-forming cells). T

Answer 8

bone master gene Runx-2

Question 9

osteoblasts fnx

Answer 9

produce bone specific proteins and begin to deposit radiating spicules of osteoid matrix (pre-bone) around them. Further osteoblast activity results in mineralization of the osteoid matrix.

Question 10

What bones are formed by intramembranous ossification?

Answer 10

Bones formed by this method include the flat bones of the face and skull. Growth of these bones is achieved
by adding bone to the outer surface and removing it from the inner surface.

Question 11

method of forming bone that makes use of Cartilage Intermediates (models).

Answer 11

Endochondral Ossification
(The mesenchyme initially aggregates into a pre-skeletal mesenchymal condensation)

Question 12

Centrally placed cells in Endochondral ossification express what gene:

Answer 12

express the cartilage master gene Sox-9 and differentiate into chondrocytes.

Question 13

Sox-9 master gene causes what?

Answer 13

causes differentiation into chondrocytes

Question 14

When Sox-9 is expressed… what affect does it have on chondrocytes

Answer 14

chondrocytes enlarge, secrete cartilage matrix, and form a cartilage intermediate or ‘model’ for the bone.

Question 15

mesenchymal cells at periphery of cartilage element form a fibrous capsule called the perichondrium. ______ can influence some to express Runx-2 to differentiation to osteoblasts

Answer 15

Indian hedgehod (Ihh)

Question 16

chondrocytes within the cartilage

model are influenced by Ihh (in some cases Runx2) expression and begin to hypertrophy and secrete

Answer 16

type X collagen

Question 17

Chondrocytes influenced by Ihh expression begin to hypertrophy and sectrete type X collagen… Hypertrophied chondrotcytes produce:

Answer 17

vascular endothelial growth factor (Vegf) that stimulates blood vessel ingrowth resulting in accumulation of additional osteoblasts.

Question 18

The cartilage model is eventually replaced by bone. Most bones of the body ossify by this method.

Answer 18

Endochondral ossification
Many of them grow lengthwise (long bones of the limbs and trunk) by maintaining a plate of cartilage at one or both ends.

Question 19

What is the role of the runx-2 gene in bone development?

Answer 19

A cell that expresses the Runx-2 will become an Osteoblast

Question 20

A cell that expressed the Sox-9 will become a

Answer 20

Chondroblast.

Question 21

These skeletal tissue forming master genes in turn stimulate the expression of additional genes specific to osteoblasts or chondroblasts resulting in the formation of bone or cartilage.

Answer 21

Sox-9 and Runx-2

Question 22

What is the Primary Ossification Center

Answer 22

Primary Ossification Center is the area of a pre-skeletal mesenchyme condensation or cartilage intermediate that is the First to Ossify. In long bones, it is usually in the center of the shaft, while in flat bones it is usually in the center of the mesenchyme condensation. A bone may have more than one primary ossification center

Question 23

Secondary Ossification Center

Answer 23

additional areas of ossification that appear
in the Prenatal, Postnatal, or Post pubertal period
appear in the epiphyses of long bones during the first few years after birth or the tips of vertebrae processes and the cranial and caudal surfaces of vertebral bodies after puberty.disappear by age 20 to 30

Question 24

amount of Epiphyseal Cartilage Retained in the Skeleton.

Answer 24

Bone Age

Question 25

useful as an indicator of skeletal growth and maturation.

Answer 25

Bone age

Question 26

How can a radiologist determine bone age

Answer 26

1) the appearance of calcified material in the diaphysis and/or the epiphysis and for each bone and sex;
2) the disappearance of the dark line representing
the epiphyseal cartilage plate indicates that the epiphysis has closed, i.e., no cartilage remains.

Question 27

Person has short extremeties proximally and a shortened skull base dt epiphyseal cartilage closing early… cranium enlarges and face looks small. Trunk is normal

Answer 27

achondroplasia

Question 28

Achondroplasia is due to:

Answer 28

defect in the Fgf receptor 3 gene that affects cartilage formation

Question 29

Mental state of achondroplasia

Answer 29

mentally astute and generally do not have associated skeletal or ear anomalies. In 80% of individuals with this
condition the cause is a new mutation, but it has been known to be transmitted as an autosomal dominant.

Question 30

due to interrupted bone growth because of insufficient production of certain pituitary derived hormones such as growth hormone.

Answer 30

Pituitary based dwarfism

Question 31

A severe deficiency of thyroid hormone can also cause individuals to have

Answer 31

short stature as well as anomalous development of the nervous system and other organs. This condition, cretinism, is associated with advanced paternal age.

Question 32

condition of overgrowth. It is usually caused by overproduction of pituitary hormones, primarily growth hormone. If over production of pituitary hormones occurs before epiphyseal plates close, it leads to increased stature.

Answer 32

Gigantism

Question 33

• This condition results from a defect in fibrillin production.

Answer 33

Marfan’s Syndrome

Question 34

Findings of Marfans

Answer 34

elongated, thin, spider like digits on the hands and feet (arachnodactyly) and tall stature. Aortic aneurysms are also associated with this condition

Question 35

A family of diseases characterized by defects in

lysosomal enzymes that degrade various proteoglycan molecules.

Answer 35

Mucopolysaccharidoses -

Question 36

Findings of Mucopolysaccaridoses

Answer 36

distortion of the face and skull. In addition to skeletal

anomalies there are ocular and CNS anomalies

Question 37

Results from a defect in type I collagen.

Answer 37

Osteogenesis Imperfecta -

Question 38

Osteogenesis Imperfecta

Answer 38

bones are brittle and easily fracture. Multiple fractures are
common and it can be life threatening. bluing of the sclera, hearing loss, growth restriction, kyphoscoliosis and
macrocephaly.