Appendicular System Development Flashcards
The first week of gestation includes:
- Fertilization of the egg by sperm
- Cleavage (series of mitotic division)
- Implantation (zygote implants into uterine wall)
- Formation of the blastocyst
The second week of gestation includes:
Reorganization of the blastocyst into a bilaminar embryonic germ disk
What is the first step in the third week of gestation?
Primitive streak formation
What marks the beginning of gastrulation?
Primitive streak formation
Describe the second step of the third week of gestation.
What is formed at this time?
Epiblast cells proliferate into hypoblast, displacing hypoblastic cells.
Newly arrived epiblast cells form the endoderm.
Describe the third step of the third week of gestation.
What is formed at this time?
Epiblast cells proliferate into the space between the epiblast and endoderm.
These cells form the mesoderm.
When does gastrulation occur?
Week 3
Around day 15, ending by day 18
gastrulation
What do the remaining epiblast form?
Ectoderm
week 2 of gestation
The bilaminar embryonic germ disk into what two sections of cells?
Epiblast and hypoblast
week 3 of gestation
What are the four steps of gastrulation?
- Primitive streak formation
- Endoderm formation
- Mesoderm formation
- Ectoderm formation
How are the notochordal process and prechordal plate formed?
Newly formed mesoderm cells migrate through the primitive streak and knot, condensing along the midline
When newly formed mesoderm cells migrate through the primitive streak and knot, and condense along the midline, what is formed?
The notochordal process and prechordal plate
What does the notochordal process become?
The notochord
When the notochordal process becomes the notochord, overlying ectoderm is stimulated into…
neural tissue
When is the development of somites initiated?
When the notochordal process becomes the notochord
When are the fates of certain cells in the nervous system specified?
When the notochordal process becomes the notochord
When the notochord and prechordal plate approximate each other, inductive changes occur that trigger the formation of the…
neural plate in the ectoderm
The neural plate in the ectoderm overlies the…
notochord
What does the neural plate give rise to?
Most of the central nervous system
What is neuralation?
The process that forms the neural tube from the neural plate
What are the three types of mesoderm?
- Paraxial
- Intermediate
- Lateral plate
What are the three parts of the somite?
- Dermatome
- Sclerotome
- Myotome
The limb bud has a core of…
lateral plate mesoderm
The limb bud is surrounded by…
ectoderm
Growth of the limb bud occurs via…
mitosis of mesodermal cells
Growth of the limb bud induces formation of the…
apical ectodermal ridge
The apical ectodermal ridge induces the underlying mesoderm to…
increase mitosis, growing the limb bud
The apical ectodermal ridge forms a progressive zone that…
controls and organizes the proximodistal development of the limb
When does differentiation of the limb bud occur?
between weeks 5 and 8
As the apical ectodermal ridge degenerates, what happens?
It defines regions where cell death occurs to form the digits
What are some dysmorphologies resulting from AER dysfunction?
Syndactyly (webbing)
Polydactyly
Amelia (lack or incomplete formation of AER)
Combinations
The limb bud consists of… that interacts with the AER to direct the overall shape of the future limb
lateral plate mesoderm
Describe differential growth
The dorsal half grows faster than the ventral half, causing the limbs to occupy a position along the ventral body wall
What cells migrate into a developing limb bud?
Lateral plate mesoderm
Myoblasts
Neural crest cells
Lower motor neuron axonal sprouts
limb bud growth
The lateral plate mesoderm gives rise to what?
The connective tissues, bones, and some blood vessels
limb bud growth
Where do myoblasts migrate from?
What do they form?
They migrate from the somite and form limb muscles
limb bud growth
Neural crest cells migrate and form…
pigment cells
limb bud growth
Where do lower motor neuron axonal sprouts from ventral horn cells migrate from?
The neural tube, following migrating mass of muscle tissue
What kind of cells migrate from the myotome into the limb bud to form musculature?
Myogenic cells
After myogenic cells form limb musculature, what happens to remaining cells in the myotome?
Remaining myogenic cells form hypomeres (hypaxial mm.) and epimeres (epaxial mm.)
What do myogenic cells mature into when they reach the limb bud?
Myoblasts
Describe the masses of myoblasts in the upper limb.
Ventral mass: flexors and pronators
Dorsal mass: extensors and supinators
Describe the masses of myoblasts in the upper limb.
Ventral mass: flexors and adductors
Dorsal mass: extensors and abductors
What somite levels are associated with upper limb?
C4-T2
What somite levels are associated with lower limb?
L1-S2
Limb rotation results in:
Dermatomal patterning of limbs
What are the two acceptable dermatomal maps?
Foerster (1933) and Garrett (1948)
