Embryology 1 - Fertilization to Gastrulation (Week 8) Flashcards
1
Q
True or False: We start out as one totipotent cell
A
True
2
Q
An organism that breathes no air, does not use the digestive tract, and lives in a sterile environment is referred to as what?
A
a fetus
3
Q
An air-breathing organism with a functional GI tract that quickly becomes colonized by microbial flora is referred to as what?
A
a newborn
Note: we undergo these massive changes within minutes after birth
4
Q
True or False: Learning embryology helps us to understand developmental/congenital disorders (e.g., DiGeorge Syndrome, ectopic pregnancy, neural tube defects, etc.), infertility, and referred pain
A
True
5
Q
Where are oocytes (female haploid gametes) produce?
A
the ovaries
6
Q
Production of which hormones occurs in the ovaries?
A
progesterone and estrogens
7
Q
Which structure receives the oocyte from the ovaries?
A
the uterine tube/fallopian tube
8
Q
Where does the sperm fertilize the oocyte?
A
the uterine tube/fallopian tube
9
Q
Where do the embryo, placenta, and membranes develop?
A
the uterus
10
Q
The site where the maternal and embryonic vasculature exchange substances
A
the placenta
11
Q
A __________ (haploid/diploid) germ cell undergoes meiosis to produce a unique __________ (haploid/diploid) gamete
A
diploid, haploid
12
Q
How do haploid gametes become “unique”?
A
crossing over (mixing of maternal and paternal chromatids during prophase I to end up with “mixed” chromatids)
13
Q
True or False: Meiosis is completed before the sperm penetrates the oocyte
A
False.
Meiosis is not completed in an oocyte UNTIL the sperm penetrates it
14
Q
We can refer to the fusion of the spermatic pronucleus and the oocyte pronucleus as?
A
fertilization
15
Q
A single, fertilized, diploid cell (combination of spermatic and oocyte genetic material = diploid cell) is known as?
A
a zygote
Note: a zygote has NOT divided yet
16
Q
Females are born with a certain number of diploid oocytes that have been “paused” at what stage?
A
first stage of meiosis
Note: meiosis does not resume until AFTER puberty
17
Q
After puberty, the ovaries release an _______ each cycle into the uterine tubes
A
ovum
18
Q
The oocyte will not complete meiosis II unless ____________ occurs
A
fertilization
19
Q
In what part of the uterine tube specifically does fertilization usually occur?
A
the ampulla
20
Q
Before ovulation, we call the oocyte what?
A
primary oocyte
21
Q
After ovulation, we call the oocyte what?
A
secondary oocyte
22
Q
The release of a secondary oocyte from the ovarian follicle is known as?
A
ovulation
23
Q
The ovulated secondary oocyte + the zona pellucida is covered externally with granulosa cells known as what?
A
cumulus oophorus
24
Q
When the cumulus oophorus rearranges, it forms the what?
A
corona radiata
25
A successful sperm must penetrate the _____________ and inject its genetic material into the oocyte
zona pellucida
26
True or False: Zona pellucida becomes impenetrable after first sperm penetrates it
True
Note: this prevents "double fertilization"
27
How long after fertilization does the oocyte complete meiosis II + zygote completes first cell division?
24 hours
28
A morula consists of how many cells?
12-20 cells
29
A ___________ is what implants into the uterine wall
Blastocyst
(formed around day 5)
30
When sperm comes into contact with the zona pellucida, it triggers an acrosome reaction, whereby the sperm secretes ___________________, that will break down the glycoprotein membrane of the zona pellucida
digestive enzymes
Note: only 1 sperm will succeed
31
a haploid germ cell is also known as
a gamete
(oocyte = gamete from ovaries; sperm = gamete from testes)
32
the protein coat that surrounds an oocyte and eventually the early embryo
zona pellucida
33
a multicellular organism, prior to the fetal stage (~ from fertilization to end of week 7) is known as?
an embryo
34
a multicellular organism, from the end of the embryonic stage (week 8) to birth is also known as?
a fetus
35
___________ is another name for newborn
neonate
36
cells formed during development that do not become part of the neonatal organism (but contribute to the fetal membranes)
extraembryonic cells
note: eventually contributes to the placenta
37
16 cell stage of an embryo
morula
note: no blastocoel in this stage
38
a spherical mass of cells that is composed of a trophoblast that surrounds a fluid cavity (blastocoel) and an inner cell mass (embryoblast)
blastocyst
39
What do we call the cell division in the early embryo, whereby each division does not increase the size of the embryo but instead results in smaller and smaller cells?
cleavage
40
a cell that is totipotent and is present during very early development (e.g., first week) is called?
blastomere (every single cell that makes the embryo in the first week)
41
a cell that can become any cell
totipotent cell
42
when the embryo contacts and becomes surrounded by the endometrium of the uterus
implantation
43
Days 1-3 of development
- embryo develops from zygote to a sphere-shaped cluster of cells surrounded by the zona pellucida
- 12-32 cell stage (morula)
- cell divisions known as cleavage
- cells known as blastomeres (which are all genetically identical = embryonic stem cells)
44
Days 4-5 of development
- a fluid-filled cavity develops within the embryo
- four structures can be noted:
1) trophoblast (layer of cells on the outside of the sphere, covered by the 2) zona pellucida); many of these cells go on to develop into membranes of placenta
3) embryoblast (inner cell mass); surrounded by the trophoblast; these cells develop into the embryo
4) blastocoel (the fluid-filled cavity within the sphere)
45
The epithelial cells of the uterine tube are equipped with _________ that "wave" in a single direction
cilia
Note: ciliary movement increases as progesterone levels increase (secretion peaks shortly after ovulation)
46
Where does the blastocyst arrive after about 5 days?
the superior aspect of the uterus (the fundus)
47
What are some of the roles of the zona pellucida during early development?
- barrier that ensures only one sperm fertilizes an oocyte
- porous (allows communication between the embryo and the maternal reproductive structures
- protects the embryo from immunologic defenses
- acts as a signal to help with differentiation of trophoblast cells
- prevents premature implantation of the embryo
- prevents the blastomeres from dissociating (helps them stay together)
48
When does the embryo "hatch" out of the zona pellucida?
day 6
Note: the zona pellucida prevents implantation of the embryo, but once it hatches, it is ready to come into contact with the endometrium and implant itself
49
What is a complication that can happen when the embryo implants too early?
ectopic pregnancy
50
What part of the endometrium binds to the trophoblast of the blastocyst?
small apical processes known as pinopods
Note: adhesion is mediated by selectin (which binds to mucins expressed on the endometrial epithelium) and integrin binding
.. results in blastocyst invading into the endometrium
51
Once the trophoblast invades the endometrial epithelium, it forms two layers: _____________ and ________________
This occurs during ~ day 5-6
cytotrophoblast (inner layer),
syncytiotrophoblast (outer layer)
52
The syncytiotrophoblast develops into a ___________ (mononuclear/multinuclear) cell mass where the borders between cells are indistinct (looks more like a blob)
multinuclear
53
What does the syncytiotrophoblast secrete?
human chorionic gonadotropin (hCG)
Note: hCG prevents the shedding of the endometrium (and loss of the embryo) by maintaining ovarian secretion of steroid hormones (e.g., progesterone)
Note: hCG is the hormone detected in pregnancy tests
54
As the syncytiotrophoblast invades the stroma (just below the epithelium), the _______________ (aka embryoblast) differentiates into two distinct layers: ____________ and ______________
This happens @ ~ day 6-7 (end of week 1)
inner cell mass,
epiblast (becomes the actual embryo/"embryo proper"),
hypoblast (aka "primary endoderm"; lines the blastocystic cavity and forms the primary yolk sac)
55
a fluid-filled cavity
(week 2 & 3)
coelom
56
the process of forming three embryonic germ layers
gastrulation
57
What are the 3 embryonic germ layers?
1) ectoderm (exterior)
2) endoderm (interior)
3) mesoderm (between ectoderm and endoderm)
58
True or False: the endoderm and mesoderm can also be extra-embryonic. The formation of extra-embryonic endoderm and mesoderm is NOT classified as gastrulation.
True
59
towards the head region
cephalad
60
towards the "tail" region
caudad
61
When is implantation complete (approximately)?
day 10
62
umbilical vesicle is synonymous with what?
yolk sac
63
Stromal cells undergo decidualization and become known as decidual cells.
Decidual cells accumulate _________ and __________ throughout the uterus
glycogen, lipids
64
Any time the syncytiotrophoblast contacts a decidual cell, the decidual cell is programmed to undergo ___________
apoptosis
Note: this releases the stored nutrients (glucose and lipids) so that the embryo has nutrients to grow
65
The epiblast enlarges and gives rise to _______________
amnioblasts (cells that surround the developing amniotic cavity)
66
Fluid accumulating between the extraembryonic mesodermal cells to form another cavity is known as the what?
extraembryonic coelom
67
three fluid-filled cavities that develop in the embryo:
1) umbilical vesicle (yolk sac)
2) amniotic cavity
3) extraembryonic coelom (develops into the chorionic cavity)
68
The connecting stalk eventually develops into what?
the umbilical cord
69
What are the two layers of the extraembryonic mesoderm?
1) extraembryonic splanchnic mesoderm (surrounds the umbilical vesicle)
2) extraembryonic somatic mesoderm (just underneath the cytotrophoblast, inner lining of the chorionic sac)
70
What is the chorion/wall of the chorionic sac comprised of?
- extraembryonic somatic mesoderm
- trophoblast (syncytiotrophoblast + cytotrophoblast)
Note: the chorionic SAC is everything inside of this
71
The chorionic sac encloses the ___________ and its cavities
embryo
72
The extraembryonic coelom becomes the ____________ by day 14
chorionic cavity
73
When syncytiotrophoblasts contact endometrial blood vessels, the blood vessel deteriorates and blood pools
These "little lakes" of blood are known as what?
lacunar networks
Note: these allow for more exchange of nutrients
74
How do nutrients from the oxygenated maternal blood and deteriorating decidual cells get to the embryo?
simple diffusion
Note: there is no circulation yet
75
thickened area of columnar cells, found in the cephalad region of the hypoblast, that acts as an embryonic organizing centre and is responsible for the induction of other structures
prechordal plate
Note: this forms by the end of week 2 (day 14)
76
True or False: the hypoblast is an organizer of the caudal aspect of the embryo
False.
The hypoblast organizes the head and mouth region and helps to induce the formation of structures found at the cephalad pole of the embryo
77
the process by which the three germ layers of the embryo are established
gastrulation
78
During gastrulation, the bilaminar embryonic disc becomes the _____________
trilaminar embryonic disc
79
During gastrulation, the embryo may be referred to as the _________
gastrula
80
thickened linear band in the median plane of the dorsal aspect of the embryonic disc that forms at the beginning of the 3rd week
primitive streak
81
True or False: The primitive streak initiates the caudal region of the epiblast
True
82
Cells at the cephalad end of the primitive streak proliferate to form what?
primitive node
83
A narrow groove that develops in the primitive streak
primitive groove
Note: primitive groove is continuous with a small depression in the primitive node, known as the primitive pit
84
As the cells leave the deep surface of the streak, they form what?
the mesenchyme
85
What is mesenchyme?
embryonic connective tissue which forms the supporting tissues of the embryo (i.e., embryonic connective tissue)
Note: mesenchyme --> forms mesoblastic cells --> which form intraembryonic or embryonic mesoderm
86
When the hypoblast is displaced by cells from the epiblast, it forms what?
embryonic endoderm
87
Cells remaining in the epiblast form what?
embryonic ectoderm
88
___________ cells derived from the primitive streak migrate widely and differentiate into diverse types of cells (e.g., fibroblasts, chondroblasts, osteoblasts, etc.)
Mesenchymal
89
True or False: Eventually, the primitive streak diminishes in size and becomes an insignificant structure in the sacrococcygeal region, and disappears by the 4th week
True
