Basics Of Embryology I Flashcards
Sperm cells in meiosis
4 viable haploid cells
Egg in meiosis
1 viable haploid cell and 3 polar bodies
Meiosis
- Specialized process of cell division that occurs only in the germ line
- diploid germ cell replicated DNA, has 2 divisions and yields 4 haploid cells
Mitosis
Normal cell division
-dipolide 2N replicates DNA with one division, 2 daughter cells
Day 0
Zygote is formed
Once a haploid sperm cell fuses with the haploid egg, the egg is then called a
Zygote
When is the pronuclear stage?
Day 0
When is the 2-cell stage?
Day 1 (24 hours)
When is the 4 cell stage?
Day 2 (48 hours)
When is the 8 cell stage
Day 3 (72 hours)
When is the morula formed
Day 4 (96 hours)
When does the blastocyst form?
Day 5 (120 hours)
When does fertilization happen?
Day 0
After initial meiosis
Its then all mitosis
When does cleavage happen?
Day 1
Cleavage
The zygote initiates a rapid serious of mitotic cell divisions. The cells increase in the number but the zygote does not increase in size. The cells still maintain contact even after dividing
What are the daughter cells after cleavage called?
Blastomeres
When do you first start seeing blastomeres?
Day 1
What happens once the cells get to the 8 cell phase?
They begin to undergo compaction. They become adhered to one another by tight junctions
When does compaction occur
Day 3
What is the embryo called when it has 16-32 cells?
Morula
When does the morula form
Day 4
Inner cell mass (embryoblast)
With compaction, some blastomeres segregate to the center of the morula and others to the outside. The centrally placed blastomeres are now called this
Trophoblasts
With compaction, some blastomeres segregate to the center of the morula and others to the outside. The peripherally placed blastomeres are now called this
What does the inner cell mass give rise to?
The embryo proper
What is the primary source of the fetal component of?
Placenta
Formation of blastocyst
By 4 days, the morula (consisting of about 30 cells), begins to absorb fluid. As the hydrostatic pressure of the fluid increases, a large cavity called the blastocyst cavities (blastocoel) forms within the morula
When does the blastocyst form
Day 5 (96 hours(
Embryonic pole
The side of the blastocyst that contains the inner cell mass
The abembryonic pole
The side of the blastocyst that contains the trophoblasts
Where does fertilization occur
Fallopian tubes
When does the morula reach the uterus
Between 3 and 4 days
Corpus luteum
- pouch left over in ovary that produces hormones if fertilization occurs
- progesterone
- will degenerate if not fertilized
- aids in implantation
- gets uterine wall ready
Decidual cells
Produce hormones
-also allows blastocyst embedding into wall
Decidual reaction
Adjacent cells of the endometrial stroma respond to its presence and to the progesterone secreted by the corpus luteum by differentiating into metabolically active, secretory cells called decidual cells.
When does the blastocyst form two epithelial layers
Day 8
What are the two epithelial layers that the blastocyst forms?
- distinct external latter of columnar cells called the epiblast
- internal layer of cuboidal cells called the hypoblasts (primitive endoderm)
Blue
Epiblast or ectoderm
Yellow
Hypoblast or endoderm
Red
Mesoderm
What is the resulting two-altered embryoblast called
The bilaminar embryonic disc.
What is dorsal
Epiblast
What is ventral
Hypoblast
Amniotic cavity
- the first new cavity to form during the second week
- appears on day 8 as fluid begins to collect between cells of the epiblast and overlying trophoblasts
When does the amniotic cavity form
Second week (day 8)
When is the embryo completely implanted
By nine days
When do cells begin to migrate
Day 9
What is the lining of the amnion
Layer of epic last cells expands towards the embryonic pole and differentiates into a thin membrane separating the new cavity
What cells form the amniotic cavity
Epiblasts
What cells form the primary yolk sac
Hypoblasts
Extrembryonic mesoderm
Formed in the second week.
Supporting structure
-placenta and barrier
Chorion
- days 11-12, extraembryonic membrane mesoderm expands between the amnion.
- days 12-13, the extraembryonic mesoderm splits into two layers; one coating the outside of the Heuser’s membrane and the other lining the inside of the cytotrophoblast. The space between the two layers is the chorionic cavity
What happens to the primary yolk sac on days 12 and 13
The chorion is being formed, and the extraembryonic mesenchyme is pinching off the blastocyst in the middle, producing remnants of the primary yolk sac in the back and the definitive yolk sac in the front
What happens to the primary yolk sac at end of second week?
The definitive yolk sac loses contact with the remnants of the primary yolk sac, and the bilaminar embryonic disc with its dorsal amnion and ventral yolk sac is suspended by a thick connecting stalk
Bilaminar embryo
- 2 layer disc
- where the epiblast and the hypo last touch
Major site of hematopoesis
Extraembryonic mesoderm
Yolk sac after the 4th week
Rapidly overgrown by the developing embryonic disc
Meckel’s diverticulum
A digestive tract anomaly from the remanants of the yolk sac
