Term
| Provide a full description of the events that occur from fertilization to implantation into uterine wall (assuming we're describing human embryology) |
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Definition
*Sperm penetrates zona pellucida
*Oocyte completes second meiotic division (forms the polar body that just kinda hangs out)
*The pronuclei merge (DNA from mom + dad), forming diploid nucleus of the zygote
*Cleavage (mitotic cell divisions; total number of cells increase without actual increase in size of the zygote overall) occurs, forming the morula
*Morula compacts and cells form tight junctions
*Cells start differentiating, making an inner and outer layer of cells
*Cavitation occurs (hollowing of the ball of cells), allowing fluid to fill the hollowed center, which now forms the blastocyst. The outer and inner layer of cells are now officially termed "inner cell mass" and "trophoblast"
*Zona pellucida dissolves once embryo reaches the uterus and the embryo "hatches"
*The embryo implants into the wall of uterus |
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Term
| When is the embryonic phase completed? What is the organism called at that point? |
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Definition
| When the developing organism begins to resemble its mature form. It is now considered a fetus. |
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Term
| What is unique about sheep and bovine embryo, as depicted in the class notes? |
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Definition
The embryo goes through similar series of events that we have learned, however, the trophoblast elongates before attaching itself to the uterus.
The extra-embryonic tissues take up much of the uterine horn that it is fixated in as the embryo grows and develops.
Additionally, the notes depict bovine and sheep being a non-invasive implantation species; the embryo doesn't implant into the uterine wall like in humans, but rather adheres to it (like velcro) |
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Term
| What controls early embryo development up to the 8 to 16 cell stage? |
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Definition
The accumulated maternal RNA and proteins (accumulated during oogenesis). The embryonic genome activates and slowly takes over as the maternal RNA and protein slowly degrade.
Note: think about why the embryonic genome kicks in after fertilization- at fertilization, that's when the zygote gets its complete genome. Something that doesn't exist can't regulate or control the very early stage of development until it has been created and grown a little bit. |
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Term
| Why can there be differences between uteruses and trophoblasts between different species? |
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Definition
Different species have different kinds of interactions based on how they attach to the uterus.
For example, humans, rodents, and carnivores are invasive (the trophoblast actually buries into the endometrium of the uterus) whereas domestic species (like bovine or sheep) are non-invasive and attach to the uterus like velcro.
The kind of interaction just depends on the species. |
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Term
| The bilaminar/embryonic disk is essential for forming what? |
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Definition
| The three primary germ layers |
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Term
| What two layers does the bilaminar disk consist of? |
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Definition
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Term
| What is the fate of the epiblast? |
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Definition
| Becomes the future embryo |
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Term
| What is the fate of the hypoblast? |
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Definition
| Becomes the extra embryonic tissues |
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Term
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Definition
| The development of the three-layer embryo |
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Term
| What is the primitive streak? |
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Definition
| An invagination on the embryonic/bilaminar disk |
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Term
| How is the middle germ layer formed? |
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Definition
| Through the primitive streak, where epiblast cells get in-between the two existing layers by migrating and then proliferating |
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Term
| What are the three germ layers? |
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Definition
Ectoderm (outermost)
Mesoderm (middle layer)
Endoderm (innermost) |
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Term
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Definition
| Formation of the neural plate and neural tube |
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Term
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Definition
| Bilaterally paired blocks of mesoderm that form along the neural tube of the developing embryo |
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Term
| What do somites develop into? |
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Definition
Sclerotome and dermomyotome
(Dermomyotome is comprised of the dermatome and myotome) |
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Term
| What does the sclerotome develop into? |
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Definition
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Term
| What does the dermatome develop into? |
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Definition
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Term
| What does the myotome develop into? |
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Definition
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Term
| Spina bifida is a result of... |
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Definition
| The unsuccessful closure of the neural tube |
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Term
| ______ and _______ of epiblast cells "in-between" the two layers of the embryonic disc form the third, middle layer |
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Definition
Proliferation and migration
The cells migrate in between the two layers and then proliferate, increasing the total number of cells in that layer. |
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Term
| Formation of the 3 primary germ layers begins with the formation of the |
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Definition
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Term
| What form the peripheral nerve cells? |
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Definition
| Some neural crest cells that have migrated during neurolation |
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Term
| Difference between primitive streak and the neural groove (if looking at a diagram and needing to label it)? |
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Definition
| Primitive streak has that very slight U shape whereas the neural groove is much steeper, looking more like a taller V |
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Term
| How does the somites grow (do they start in any particular area of the embryo and develop from there)? |
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Definition
| Somites are formed in the middle of the embryo on both sides of the neural tube and then continue to form more somites, extending out caudally and cranially (towards head and towards butt) |
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Term
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Definition
Helps regulate cell differentiation
cells that are closer to the notochord get the same signal as ones that are farther away from the notochord (paracrine cell signaling). However, closer cells will receive an abundance of this signal vs farther away ones not receiving as much. This difference in signal amplification aids in the different development of cells. |
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Term
What term best describes this, as depicted in class notes?
How could you determine this if another diagram was given to you?
[image] |
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Definition
Fertilization
You can see two pronuclei (dots) coming together, with the single polar body within the zona pellucida at the top. Could also possibly see one nucleus, showing fertilization just occurred |
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Term
What term best describes this, as depicted in class notes?
How could you determine this if another diagram was given to you?
[image] |
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Definition
Cleavage
You can see more than one cell with a single nucleus within the zona pellucida. The number could vary, but they are a random mess, not compact or organized |
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Term
What term best describes this, as depicted in class notes?
How could you determine this if another diagram was given to you?
[image] |
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Definition
Compaction
The random mess of cells within the zona are more organized or in-line. Could depict the tight cell junctions |
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Term
What term best describes this, as depicted in class notes?
How could you determine this if another diagram was given to you?
[image] |
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Definition
Differentiation
The cells within the zona are still more in-line and organized, could be depicting an increased cell number but still all in line. Could show different colors indicating the ICM is forming |
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Term
What term best describes this, as depicted in class notes?
How could you determine this if another diagram was given to you?
[image] |
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Definition
Cavitation
The inner cell mass is clumped in one area of the trophoblast cells along with an "empty" center (fluid filled or blastocoelic cavity) |
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Term
What term best describes this, as depicted in class notes?
How could you determine this if another diagram was given to you?
[image] |
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Definition
Zona hatching
The ring of trophoblasts with the ICM in it is leaving or does not have the zona pellucida anymore |
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Term
What term best describes this, as depicted in class notes?
How could you determine this if another diagram was given to you?
[image] |
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Definition
Implantation
you see the blastocyst nestled up to the uterine epithelium. Note that this is in humans; cattle and sheep's embryo elongate then adhere to the uterine horn instead of implanting |
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Term
What term best describes this, as depicted in class notes?
How could you determine this if another diagram was given to you?
[image] |
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Definition
cell mass differentiation
lots more cells inside the ring of trophoblast cells; not just a tiny little area any more. Hypoblast and epiblast can be depicted in two different colors |
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Term
What term best describes this, as depicted in class notes?
How could you determine this if another diagram was given to you?
[image] |
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Definition
Bilaminar disc formation
There are not any single clumped areas inside of the trophoblast ring- it just shows a "hollow" half oval type of shape for both the hypoblast and epiblast. Where the two half oval things meet is the bilaminar disc and there is literally just that there- nothing in between them (3rd layer hasn't formed yet) |
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Term
What term best describes this, as depicted in class notes?
How could you determine this if another diagram was given to you?
[image] |
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Definition
Mesoderm formation
The two half oval shapes within the trophoblast ring are squishing a middle layer. You can see the epiblast making a kidney bean type of shape, showing the primitive streak and mesoderm underneath this concaved part. |
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