13 - Zygote to Embryo 1 Flashcards
(41 cards)
The result of fertilization is the formation of a single diploid cell called ______.
A zygote.
Formation of the zygote initiations the process of _______?
Prenatal embryonic development.
We can collectively group the events of the first three weeks of embryonic development as __________?
Embryogenesis - the formation of an embryo.
Human embryonic development is traditionally divided into two periods called _____ and _____.
The embryonic period
The fetal period.
What occurs during the embryonic period?
Zygote (1 cell) becomes an embryo with a body plan, 3 layers, and 3 axis.
3 layers become 4 tissues, which become organs and organ systems.
Segmentation, head, link and trunk formation, and embryo folding occurs.
How long is the embryonic period?
8 weeks, the end of which gets you to an embryo.
Describe the fetal period of embryonic development?
Unborn baby - growth and maturation occurs.
Continued development of some systems.
What is the perinatal period? Why is this a clinically important period?
Starts during fetal period and ends after fetal period.
From 22 weeks to 1 month after birth.
This is usually when premature births occur.
What is the neonatal period?
The first month after birth (also perinatal period).
How is human embryonic development divided in the clinics?
Into three 12 week trimesters.
When does fertilization age start? What about the gestational age?
Begins at fertilization - this is the timeline that the embryo runs on.
Starts at last menstruation - two weeks later than fertilization age.
What does it mean when you say someone is 12 weeks pregnant?
That is their gestational age.
Their fertilization (embryo) is actually only ten weeks.
What occurs during the first week of embryonic developement?
Fertilization, cleavage, blastocyst formation, bilaminal embryonic disc.
Goes from one cell to solid ball of cells to fluid filled cyst with disk.
What is the next step after zygote formation?
Cleavage.
What is compaction?
Occurs after cleavage - it’s when the cells that divided in the cleavage stage loose their distinction.
Describe the cell division during the cleavage stage?
Rapid; every 12-24 hours with NO G1 or G2.
Controlled and asynchronous.
No cell growth so the ratio of cytoplasm to nucleus goes from 600:1 to 3:1
What controls the first cell division during cleavage? When is the embryo genome activated? What is needed next?
The maternal program.
Embryo genome activated at 2-4 (4-6?) cell stage.
New proteins needed for cleavage and blastocyst formation.
Are all cleavage-stage blastomeres (cells formed by cleavage of zygote) the same? What is this knowledge the basis for?
Yes.
Basis for cloning. Nucleus of an adult cell can be removed and put into an oocyte with no nucleus to clone whatever animal the nucleus came from.
In mammalian embryos, each blastomere up to about the 8 cell stage has the potential to form _____? Whose experiment determined this?
A complete embryo if isolated and allowed to develop - Spemann experiment.
But if it stars in place during development it only contributes to part of the embryo.
How does a blastocyst form? When does this occur?
Day 4/5
- 8 cell stage has two cell lineages: outer cells and inner cells
- Compaction occurs to create a morula, a solid ball of cells
- Cavity formation in uterine cavity creates a blastocyst:
outer cells become the trophoblast and inner cells become the inner cell mass (ICM)
The ______ becomes the first tissue of the embryo which is an ______ tissue. Describe the cells in this tissue.
Trophoblast.
Epithelium: cells joined by junction and form layers. Cells polarize. Cell layer lines cavity or covers surface.
What type of tissue does the trophoblast form? What does this require?
Extra-embryonic tissue: membranes that surround the embryo but don’t form the parts of the embryo itself.
Require paternal derived alleles (genomic imprinting)
What happens to the inner cell mass?
Most of these cells become part of the embryo.
ICM remodels into bilaminar disc containing the epiblast (primitive ectoderm) upper layer and the lower hypoblast (primitive endoderm) layer.
What shape are cells in the epiblast layer? What about the hypoblast layer?
Epiblast: taller, columnar-like
Hypoblast: flatter, squamous-like
