Musculoskeletal and Limb Embryology - Acht Flashcards
Function of the notochord?
- defines the axis
- has a mechanical role in forming the neural groove and tube, somites, and musculoskeletal system
Contributes to:
vertebral bodies
intervertebral discs
What is mesenchyme?
Embryonic connective tissue
- it is derived from mesoderm and the neural crest
- mutlipotent, differentiate into myoblasts, chondroblasts, osteoblasts, fibroblasts, etc.
Significance of 4th week in development?
- Embryo transitioning into being a closed structure
- begins the formation of all organs
- time most susceptible to teratigens
What specific things are forming in the 4th week?
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
Scleretomes of each somite will eventually form?
Where in the somite are the scleretomes located?
Bones
located medially
Dermomyotomes of each somite will eventually form?
Where in the somite are the dermomyotomes located?
Skin and muscle
laterally
As bones develop, what tissue is the bone replacing?
Bone is replacing hyaline cartilage
Where are bone ossification centers before and after birth?
Before birth they are only at the center of the bone. After birth they also form at the ends and grow toward the middle
This forms the epiphyseal plates
What is an abnormality in connective tissue causing:
excessive long bone growth
Fibrillin-1 gene
Long, thin limbs
Can affect heart, vessels, bones, lungs, eyes
Marfan syndrome
Osteogenesis imperfecta
Defect in type I collagen gene in most cases Autosomal dominant or recessive Extreme bone fragility Frequent fractures Hypermobile joints
What is the difference between acromegaly and gigantism?
Acromegaly
Excess growth hormone after growth plates closed
Large, heavy bones especially face, hands and feet
Gigantism
Excess growth hormone during childhood before growth plates close
Overall large size: height and organs; normal proportions
How do you treat congentital hip?
Harness or cast to keep legs in outward and somehwat immobile position
Because of the incomplete formation of acetabulum
Vertebrae are made from?
2 adjacent segments of two adjacent scleretomes
C1 vertebra made from O4 and C1 scleretomes
C2 vertebra made from C1 and C2
What forms the nerves coming off of the spinal cord?
Von Ebner’s fissures between the dense and loose connective tissue in the scleretomes - go on to form the nerves
What is spina bifida occulta?
How do you recognize it?
The bottom of the lumbar neural arch is not formed
Tuft fg hair in this region
What is pectus excavatum?
Creates as indented-looking chest
- Can fix using surgery
- Often no symptoms, but possible that is compresses heart/lungs (fatigue, rapid pulse, resp infections, murmur, angina)
What period is the embryo’s critical period for limb development?
weeks 4-8
WHich directions do the upper and lower limbs rotate in development?
upper limb rotates 90deg laterally
lower limb rotates 90deg medially
What are the terms for no limb development, partial absence, and flipper-like extremeties?
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
What is a teratogen that causes abnormal limb development?
Thalidomide
What is syndactyly?
Webbing between digits is not removed by noraml apoptosis
The epimere will develop into what muscles?
epimere = the deep extensors of the back
hypomere = limb muscles, and trunk muscles
What is Poland syndrome?
Congenital malformation or absence
of pectoralis major muscle (unilateral)
and often including ipsilateral webbing of
the fingers.
What is Prune Belly Syndrome?
Poor development of abdominal muscles causing skin to wrinkle; undescended testicles and urinary tract problems
What kinds of bones does achondroplasia affect?
It affects only the long bones. This is why it is the most common form of dwarfism
What is the nucleus pulposis derived from?
notochord!
weird right?
What occurs in the meningocele form of spina bifida?
The neural arch is not formed. The spinal cord is normal and stays in the right spot and the meninges are forced into the gaps between the vertebrae. Forming a cyst filled with CSF
What occurs in the Myelomeningocele form of spina bifida?
The lack of neural arch allows the meninges into the gaps between the vertebrae, matters become more complicated because the spinal crd actually follows into this cystal space as well.
What is the name of the disorder characterized by a fusing of any of the cervical vertebrae?
Klippel Feil Syndrome
What is a congenital abnormality that can easily lad to scoliosis?
Hemivertebra
Somewhere in the spine there is a vertebrae that is only partially formed as wedge, making the structure all topple-y
Why can cervical ribs cuase problems like thoracic outlet syndrome?
There are a lot of vessels and nerves going through the area to supply the upper extremity
(brachial plexus, axillary nerve)
How does the AER (Apical Ectodermal ridge) help in limb development?
secretes fibroblast growth factors that induce underlying mesenchyme to proliferate, so that the limb lengthens but the distal aspect of limb is inhibited from terminal differentiation.
the limb develops from proximal to distal.
What is pattern of development of a somite to striated skeletal muscle?
Somites -> myotomes -> mesenchyme -> myoblasts -> myotubes -> multinucleated muscle fibers -> striated (skeletal) muscle
(just be familiar)
The posterior division of the ventral ramus of the ventral root supplies what muscles?
extensors of the limb
The anterior division of the ventral ramus of the ventral root supplies what muscles?
flexors of the limb
flexors of shoulder
Whats the difference between endochondral and intramembrous bone formation?
Endochondral: all bones of axial and appendicular skeleton, except part of the clavicle
3 cell types involved: chondrocytes, osteoblasts, osteoclasts
chondrocytes derived from paraxial & lateral plate mesoderm, neural crest for cartilage of face & neck; osteoclasts arise in hematopoetic system
Intramembranous: face and skull
mesenchyme cells derived from neural crest cells & paraxial mesoderm of the head give rise directly to osteoblasts
Where does the smooth muscle of the body come from?
Smooth muscle is derived from splanchnic mesoderm that lines the developing gut.
Neural crest cells contribute smooth muscle to eye muscles.
Cardiac muscle is derived from splanchnic mesoderm of the developing heart.
Small muscles of glands (myoepithelial cells) from ectoderm
