General Embryology Flashcards
What makes up the first trimester?
preimplantation period and embryonic period
What makes up the last 2 trimesters?
Fetal period
Steps of prenatal development
1) fertilization and formation of the zygote
2) mitosis lead to formation of the blastocyst, which forms a fluid filled vesicle and implants in the uterine wall
- will then fold into 3 distinct germ layers
What factors drive development?
growth factors, and cell adhesion molecules act through signaling complexes which inactivate various transcription factors
-leads to proliferation, differentiation or apoptosis
What does bone morphogenic protein signaling do?
- at gastrulation it switch between epidermal vs. neural fate
- induction, formation, determination, and migration of neural crest cells
- patterning and formation of facial primordial
- craniofacial skeletogenesis
- Negative regulator of myogenesis –> makes bone instead of muscle
- regulator of early tooth morphogenesis and differentiation
What genes are responsible for genetic control of embryological patterning?
1) Hox genes: function in patterning the body axis and determine where limbs and other body segments will grow in developing fetus
2) Msx genes: control cellular process of differentiation and proliferation during development
3) DLX genes: control development of ectodermal tissues derived form lateral border of the neural plate
- control patterning of the branchial arch skeleton
- expressed in developing bone and regulate limb development
4) Shh: plays an important role in the early induction of facial primordia
What are the importance of the cell adhesion molecules?
- Important for differentiation and positioning
1) Cadherins: calcium-dependent
2) CAM: calcium-independent
- neuroectoderm progenitors express N-CAM
- Skin ectoderm progenitors express L-CAM
Pre implantation –> fertilization
- first week after concept
- formation of the zygote
- mitosis leads to the blastocyst
What happens during the cleavage stage?
- this is the process of the zygote undergoing mitosis
- solid ball of cells called the morula
- Lasts till 3 distinct germ layers have formed
- embryoblast forms the embryo proper
What occurs during the embryonic period? (2-8wks)
- This is where PATTERNING happens
- formation of the pharyngeal arches, somite development, face development, palate and tongue formation
What is pattering?
- Axial specifications –> which end is up
- Segmentation –> what forms in between each end
- tissue and organ specialization begins
- development of dentition
- Induction: when one group of cells tells another group of cells to do something, which are said to be competent to do something
- morphogenesis: cell migration, interactions, and proliferations causing the development of specific structures
What is gastrulation?
the formation of the 3 germ layers, occurs around 3 weeks
How does the bilaminar germ disk form?
1) after the blastocyst implants, the embryoblast differentiates
2) Dorsal cells (epiblast = High columnar) reorganize to form amniotic cavity
3) Ventral cells (hypoblast = small cuboidal) form the roof of the secondary yolk sac
- overall this establishes the embryo axis
How does the formation of the primitive streak form?
- occurs after formation of the bilaminar disc
- a groove forms by the epiblast cells, proliferate and budge out to either side
- defines the symmetry along a rostral-caudal axis
- the prochordal plate forms at the rostral end, where the ectoderm curves around and integrates with the endoderm
What is the beginning step in the process of gastrulation?
- ectodermal cells invaginate at the primitive node, form the primitive pit
- here cells migrate between ectoderm and endoderm
- the notochord forms –> vertebral precursor
- ectodermal cells migrate and invaginate spreading laterally between the two layers
- hypoblast cells are pushed out of the way
- epiblast cells form the true endoderm
- Everywhere except at the prochordal plate and the cecal plate the notochord and mesoderm totally separate the ectoderm and endoderm
How does formation of the mesoderm occur?
- medial epiblast cells lose their cell-cell adhesions
- become motile and invade inwards
- these cells are interspersed in matrix and have no polarity
- attachment proteins –> E- to N-cadherin
What is a mesenchymal cell?
no cell polarity, loss of cell adhesion, ability to migrate and invade, low level of E-cadherin, and high level of N-cadherin
What makes up the triploblastic embryo?
- Cephalic end defined by the prochordal plate
- the head fold is going to form the oropharyngeal membrane at the prochordal plate end –> no mesoderm between ectoderm and endoderm
- Location of stomodeum (primitive mouth) will form here
What oral structures does the ectoderm give rise to?
- nervous system; epidermis and its appendages (hair, nails, sweat glands)
- epithelium lining the oral cavity, nasal cavities, and sinuses
- a part of the intramural glands
- TOOTH ENAMEL
What oral structure does the endoderm give rise to?
- epithelial lining of the respiratory and gastrointestinal tract and all associated organs
What oral structures does the mesoderm layer give rise to?
- muscles and all the structure derived form the CT (bone, cartilage, blood, DENTIN, PULP, CEMENTUM, and PDL)
What occurs during post gastrulation?
1) differentiation of the nervous system
2) formation/migration of the neural crest
3) embryo folding: head fold, lateral folds, and tail fold
How does the nervous system form?
- begins with formation of the neuroectoderm; specialized group of cells that differentiate from the ectoderm
- localized to the neural plate of the embryo, a central band of cells that extends the length of the embryo, form the cephalic end to the caudal end
- continuation of growth leads to formation of the neural groove
- Closure is important point in development –> where spina bifida can occur
What is the fate of the mesoderm?
1) paraxial: cartilage, segmented
2) intermediate: kidneys, gonads
3) lateral plate: heart, gut
- differentiated mesoderm gives rise to the SOMITES, that are located on the sides of the developing central nervous system
