Development of Bone and Muscle--Ach - Sheet1 Flashcards
apical ectodermal ridge (AER)
AER plays a major role in limb formation by inducing proliferation of undifferentiated mesenchymal cells (via fibroblast growth factors). As the limb grows, those cells farther from the AER differentiate into cartilage and muscle. Thus the limb develops from proximal to distal.
Cartilage/muscle differentiation begins in __________ of limb and progresses in _________ direction.
the proximal part; a proximal to distal
The notochord induces development of the __________.
neural plate and neural tube
The neural tube induces formation of _____.
the somites
osteoclasts arise from the …..
hematopoetic system
Somites (somitomeres) derive from _____.
paraxial mesoderm.
Week four is a critical period in development. Why?
Neural tube begins to close Cephalo-caudal and lateral folding Appearance of somites/somitomeres Genesis of organ systems Appearance of pharyngeal arches (face and neck) Otic and optic development begins ****Limb buds appear****
How many pairs of somitomeres and somites?
7 somitomeres (contribute mesoderm to head and neck) and ~35 somites (contribute mesoderm to the rest of body)
3 types of joints
Fibrous joints include cranial sutures, interosseus membranes between radius and ulna, tibia and fibula, ligamentous joints of spine
Fibrocartilaginous joints include costal sternal joints, pubic symphysis, intervertebral disc/ vertebra
Synovial joints are our stereotypical moveable joint like those in the limbs (femur with pelvis, femur with tibia, metacarpals with phalanges, etc)
Marfan Syndrome
example of locus heterogeneity. caused by a defect in fibrillin. Connective tissue disorder causes excessive long bone growth; Fibrillin-1 gene; Long, thin limbs
Can affect heart, vessels, bones, lungs, eyes
LINCOLN LIKELY HAD MARFAN SYNDROME
Osteogenesis imperfecta
Genetic bone disorder (brittle bone disease).
Most common form is autosomal dominant with abnormal type I collagen gene, causing:
• Multiple fractures with minimal trauma;
may occur during the birth process
• Blue sclerae r.J clue to the translucency of the connective tissue over the choroidal vems
• Hearing loss (abnormal middle ear bones)
• Dental imperfections clue to lack of dentin
Achondroplasia
Most common form of dwarfism
Affects long bones
May be autosomal dominant inheritance or spontaneous mutation of **FGFR3 gene
Brain growth and intellect usually normal
Acromegaly vs. Gigantism
Acromegaly (big bones!)–Excess growth hormone after growth plates closed
Large, heavy bones especially face, hands and feet
Gigantism (tall!)–Excess growth hormone during childhood before growth plates close
Overall large size: height and organs; normal proportions
Intersegmental mesenchyme becomes _____.
annulus fibrosis (of vertebral disc)
Notochord becomes _________.
nucleus pulposis (of vertebral disc)
The costovertebral joints are _____.
synovial joints.
Failure of closure of neural tube can result in what?
One is…. spina bifida occult –> tuft of hair on back (often in Lumbar section).
Klippel Feil Syndrome
Congenital fusion of any of the cervical vertebrae
Limb development
***Week 4 begins the critical period in limb development,
which continues through week 8. Note that bone development begins in week 3.
Location of limb buds (patterning) is controlled by homeobox (Hox) genes
Upper and lower limb bud locations…
upper limb = C5-T1. lower limb = L2-S2
Amelia
no limbs (bilateral or unilateral)
Meromelia
partial absence of limbs
Phocomelia
hand or foot-like appendage attached almost directly to torso; form of meromelia; phoco- means “seal”; flipper-like extremity
Polydactyly
Most common hand anomaly
May involve autosomal dominant trait
Extra digits may be fully formed or only soft tissues
syndactyly
Failure of apoptosis leading to fused digits or fusion
of bony components
Notice that the skeletal elements are present
In the regions where the limbs are developing, __________ surround the developing long bones to form an __________ and a __________ group.
hypaxial myoblasts; extensor (dorsal) and a flexor (ventral)
Trunk and Limb muscles (striated) are derived from __________.
paraxial mesoderm (somites)
Smooth muscle is derived from __________ that lines the developing gut.
splanchnic mesoderm
Two types of bone formation: ________ and __________.
endochondral; intramembranous
