Embryogenesis Flashcards
1
Q
Embryology begins at:
A
fertilization
2
Q
Before fertilization, the oocyte is stalled where?
A
- the beginning of the second meiotic division.
3
Q
Sperm capacitation:
A
- biochemical changes that occur to the head of the sperm that renders it able to fertilize the oocyte.
- occurs in the female uterus and uterine tube.
4
Q
What reaction allows sperm to penetrate corona radiata and zona pellucida?
A
- acrosomal reaction
- in vitro it takes about 20 sperms acrosomal reaction to penetrate the zona pellucida and allow one sperm to fertilize.
5
Q
Once a sperm reaches the zona pellucida, what occurs?
A
- The sperm then releases its acrosomal enzymes, which dissolve some of the zona to allow the sperm to reach the oocyte.
6
Q
Sperm fusion with the oocyte plasma membrane causes:
A
- an influx of calcium, which causes the cortical reaction.
7
Q
What is the cortical reaction?
A
- Enzymes from the cortical granules render the zona pellucida impermeable to other sperm, preventing polyspermia.
- polyspermia = multiple fertilization
- caused by the influx of calcium following sperm penetration of the oocyte plasma membrane.
8
Q
Following the cortical reaction, what occurs?
A
- Sperm extrudes its contents into the oocyte.
- ONLY nucleus, centrosome, & microtubules.
- Sperm have no organelles, mitochondria, or RNA.
- Oocyte completes the 2nd meiotic division.
9
Q
All the events taking place in the zygote for the first 2-3 weeks following fertilization are controlled by:
A
- mRNA already in the oocyte at the time of fertilization (maternal mRNA).
10
Q
Following the oocyte completing the 2nd meiotic division, what occurs?
A
- sperm and oocyte nuclei fuse to form zygote
- restoration of dipoid (2n) cell
11
Q
What event is the beginning of embryonic development?
A
- zygote formation when the sperm and oocyte nuclei fuse
12
Q
What occurs immediately following zygote formation?
A
- Sex of the embryo is determined.
- 1st mitotic division begins.
13
Q
Sequence of events during the cortical reaction:
A
- sperm fuse to oocyte plasma membrane
- local calcium concentration increase
- calcium tsunami
- cortical granule fusion to plasma membrane, preventing polyspermia
14
Q
Where does fertilization normally take place?
A
- the ampula of the uterine tube
15
Q
What is the zone pellucida?
A
- a glycoprotein membrane surrounding the plasma membrane of the oocyte
16
Q
The mitotic divisions occurring the first 4 days following fertilization are:
A
- symmetric, synchronous, and contained within the zona pellucida.
- day 4 = morula (32 cells)
17
Q
What occurs on post-fertilization day 5?
A
- blastocyst forms (hollow ball)
- blastocyst, releasing enzymes, hatches from the zona pellucida.
18
Q
Blastocyst structure:
A
- outer cell mass = trophoblast
- inner cell mass = embryoblast
- hollow cavity
19
Q
Trophoblast:
A
- the outer cell mass of the blastocyst that will go on to form the placenta.
20
Q
Embryoblast:
A
- the inner cell mass of the blastocyst that contains the “embryonic stem cells” that will go on to form the embryo.
21
Q
On post-fertilization day 6, what occurs?
A
- implantation of the blastocyst on the body of the uterine wall
22
Q
How does implantation occur?
A
- the cells of the trophoblast invade the lining of the body of the uterine wall
23
Q
While invading the lining of the uterine wall during implantation, what else are the trophoblast cells doing?
A
- fuse together and differentiate into a cytotrophoblast and a syncytiotrophoblast.
- allows for regional specialization of protein production.
- syncytiotrophoblast begins producing human chorionic gonadotropin (hCG).
24
Q
Implantation any place other than the body of the uterus is an:
A
- ectopic pregnancy
25
What is the most common site of ectopic pregnancy?
* ampulla of the uterine tube
26
What is the most common site of ectopic pregnancy in the peritoneal cavity?
* the rectouterine pouch
27
When is human chorionic gonadotropin (hCG) detectable in the blood following pregnancy?
* implantation
* when the trophoblast implants into the body of the uterine wall, differentiates into a syncytiotrophoblast, and begins producing hCG.
28
What are the two roles of the syncytiotrophoblast?
* produces hCG at the time of implantation.
* invades the uterine lining and induces vascular changes.
29
Follwing implantation, the embryoblast differentiates into:
* epiblast and hypoblast.
30
The hypoblast of the embryoblast sits on top of:
* the blastocyst cavity, which becomes the yolk sac
31
The epiblast of the embryoblast sits below:
* the aminotic cavity
32
When is dorsal and ventral first defined in the embryogensis?
* at the time of epiblast and hypoblast development during the second week.
33
During what week doe the syncytiotrophoblast begin to form lacunae (hollow spaces)?
* second week
* lacunae fill with maternal blood establishing a primitive utero-placental circulation in week 3.
34
When is the utero-placental circulation first noticeable?
* the third week
35
Connecting stalk:
* suspends the embryo, with its amnion and yolk sac, in the chorionic cavity
* stalk formed by extraembryonic mesoderm
* formed by the end of the third week
36
At the end of the third week, the hypoblast and epiblast cells adhere to each other in only 2 locations.
Which two?
buccopharyngeal membrane and cloacal membrane
37
When does zygotic mRNA transcription begin?
* the beginning of the fourth week
38
What is the first indication in the fourth week that zygotic transcription has begun?
* The primitive streak (groove) appears at the caudal end of the dorsal surface of the epiblast.
39
The primitive streak (groove) initiates:
gastrulation
40
Gastrulation:
* turns a bilaminar embryo into a trilaminar embryo
41
Morphologic assymmetry begins at the primitive groove, and is due to what protein?
sonic hedgehog (ssh)
42
Cells in the pimitive node/pit:
* all have a single cilia.
* cilia sweeps fluid from the right hand side of the embryo to the left hand side.
* fluid contains vesicles containing sonic hedgehog (ssh).
43
The cilia of the cells of the primitive pit cause sonic hedgehog (ssh) to:
* migrate from the right to the left side of the embryo.
* ssh stimulates gene expression on the left hand side of the embryo BEFORE the right hand side.
44
ssh stimulates gene expression on what side of the embryo first?
* left-hand side.
* due to primitive pit cells' cilia.
* sets up the morphological asymmetry of the body.
45
"sidedness" of the embryo is determined at what point in embryogenesis?
* gastrulation
* when the primitive pit's cells' cilia stimulates movement of ssh-containing vesicles to the left side of the embryo.
46
Ciliopathy:
* can cause errors in the distribution of ssh during gastrulation
* gene expression is in altered locations, morphological changes occur.
## Footnote
**SITUS INVERSUS**
47
Delamination of the primitive groove gives rise to:
(epithelial to mesenchymal)
* a three layer embryo:
* ectoderm = outer region
* mesoderm = middle region
* endoderm = inner region
* the cells of the primitive groove migrate in between the epiblast and the hypoblast. They completely replace the hypoblast.
48
The ectoderm, mesoderm, and endoderm all arise from:
* the epiblast
* the hypoblast is completely replaced by primitive groove cells
49
The epiblast cells do not invade:
* the buccopharyngeal or cloacal membranes
* because this is the only place where epiblast and hypoblast cells tightly adhere to one another.
50
How is the notochord established?
* epiblast cells of the primitive node migrate to the buccopharyngeal membrane on the midline
51
The notochord induces development of:
* the nervous system
* after gastrulation
52
What is the only remnant of the notochord in adults?
nucleus pulposus
53
What results from the union between the sperm and the oocyte?
* diploid (2n) complement of chromosomes
* cortical reaction
* formation of second polar body
* completion of the oocyte’s 2nd meiotic division
54
Similarities between the buccopharyngeal membrane and the cloacal membrane:
* both have no mesodermal layer
* both predict site of the future opening of gut tube
* both visible as a shallow depression in the ectoderm
* both will rupture
