Human Embryology Flashcards
1st _______ weeks important for cranio-facial development
eight
Normal gestationDuration: ___ +/- 2 weeks = full term____ days from first day of last menstrualperiod (LMP) or_____ days from ovulation.
40; 280 days; 266 days
Which trimesters are these?
_______ trimester: growth in weight, preparation for birth
_______ trimester: from single cell to baby-looking
________ trimester: growth in length, organogenesis
third; first; second
How long are each trimesters (in weeks)?
First trimester (~0-14 wks): from singlecell to baby-looking
Second trimester (~15-27 wks): growth inlength, organogenesis
Third trimester (~28 wks to term): growthin weight, preparation for birth
Which trimester is the most critical period for normal development?
The first trimester
NOTE: 30% of conceptions end in spontaneous abortions
Why is the first trimester is the mostcritical period for normal development? (3)
1) chromosomal abnormalities
2) abnormal sperm/ oocyte
3) improper implantation
ALSO; women know they’re pregnant ~2 months, so they may drink and smoke week (everyday)
T/F: During the first trimester, theembryo (1st 8 weeks) and fetus (8-14 weeks) are most sensitive to teratogens,including: alcohol, drugs (prescription andrecreational), cigarette smoke, elevated body temperature(hot tubs, maternal fever).
True
T/F: Paternal age is not linked with schizophrenia.
False; father’s age is linked due to increase rate of random mutations
What’s Down Syndrome? How does it occur?
DS= trisomy of chromosome 21
It occurs due to non-disjunction during meiosis
NOTE- non-disjunction is when apair of chromosomes doesn’t split off, resulting in an unequal # of chromosomes(gametes are supposed to be haploid)
1) _______: sperm + oocyte = embryo
2) _______: via cell division/cleavage, from singlecell to multicellular hollow ball.
3) _______:separating the embryonic region from the extraembryonic components (e.g.placenta) and making intimate contact with maternal tissue.
4) _______: formation of the 3 germ layers – endoderm, mesoderm and ectoderm via cellmigrations.
5) _______: formation of the brain and spinal cord fromthe ectoderm.
6) _______:from the endoderm, via cranial/caudal and bilateral body folding.
7) _______: migration to form muscle, skeleton, dermis, urogenital tract, circulatorysystem, blood and heart.
Time Zero 1) Fertilization 2) Blastocyst Formation 3) Embryonic Dis and Implantation 4) Gastrulation 5) Neurulation 6) Gut Tube Formation 7) Mesoderm Development Week 4
Each step (Except Fertilization) takes 1 week
Blastocyst Formation: What is it? What week?
Week 1; cell division/ cleavagne, from single cell to multicellular hollow ball
Fertilization: What is it? What week? Where does it occur?
Time Zero; sperm+ oocyte= embryo
Occurs: the ampullary portion of the fallopian tube
During what trimester stage can embryonic stem cells be deliberately differentiated?
Blastocyst Stage (when embryo hatches)
T/F: Cleavage is cell division accompanied by cell growth
False; it is not
Cleavage is the first next important step after fertilization. When and at what rate does it occur?
- First cleavage occurs at ~24 hr postfertilization, producing the first 2 blastomeres.
- Subsequent cell divisions every 12 hrsproduce the ~30 blastomeres of the morula.
The blastocyst forms from the______ via a process of compaction and is fluid filled.Then the blastocyst separates into2 sets of cells: ______ and _______.
morula;
trophoblast and inner cell mass
________: becomes the embryo proper and some extraembryonic tissues derives from the small collection of internal blastocyst cells
________: givesrise to the placenta, but not the embryo. derivesfrom the outer cells which become flat and make tight junctions
- Inner cell mass
* Trophoblast
Hatching of the Blastocyst:
The blastocyst emerges from the __________ 5days after fertilization.
At this time, the inner cell mass is abilaminar disc, comprising the _____ and _______.
zona pellucida
epiblast and hypoblast
T/F: Hatching is required for implantation of the blastocyst in the endometrial wall in week 2.
True!
How many days after fertilization does implantation occur?
4-6 days after fertilization, theblastocyst reaches the uterus, which is primed for implantation.
Embryonic Disc and Implantation: What is is and what week does it occur?
Week 2
separatingthe embryonic region from the extra-embryonic components (e.g. placenta) andmaking intimate contact with maternal tissue.
Describe the how the bilayered disc forms
Theinner cell mass becomes bilayered,comprising the outer epiblast layer and the inner hypoblast layer, surroundedby the trophoblast epithelium
NOTE: innercell mass= 2 layer structure
Bilayered Disc Formation:
•The______ and _______ produce extraembryonic tissues, while the ______ gives rise mostly to the embryo proper.
Trophoblast and Hypoblast
epiblast
The dorsal _________ is the normal zone for implantation.
Theembryo first attaches to, then invades the ___________, with the epiblastalways oriented first toward the uterine wall.
_________ cells (from the trophoblast) secrete proteolytic enzymes, allowing the_________ to enter the endometrial wall
Endometrium
Endometrium
Syncytiotrophoblast; blastocyst
Theinner cell mass which has formed into the bilaminar embryo (______ and _______) and the large fluid-filled space(_________).
epiblast and hypoblast;
blastocoel
What three things happens during implantation?
1) syncytiotrophoblasts generate lacunae (w/in endometrium) which fuses w/ other maternal capillaries (joins maternal/ embryonic cirulation)
2) The amniotic cavity forms around epiblast cells
3) Definitive yolk sac forms the hypoblast
Is the hypoblast considered the extraembryonic mesoderm?
yes
What does the primitive yolk sac (aka embryonic umbilical vesicle) forms?
the umbilical trunk
90% of Ectopic Pregnancies are ________, and danger isfrom rupture and subsequent hemorrhage
tubal
What 3 future germ layers reside in the epiblast before gastrulation? What are they destined to do?
1) Ectoderm- brain/ spinal cord & dermis of skin
2) Mesoderm- muscle, bone, blood, urogenital system & dermis of skin
3) Endoderm- GI & respiratory tract
The gastrulation process transforms the single layer _______ into 3 layers: ectoderm, mesoderm and endoderm.
epiblast
The ______ and _______ move initially from the epiblast through the primitive streak, while _______ stays on the surface.
endoderm and mesoderm; ectoderm
The primitive streak, where the endoderm and mesoderm moves through during gastrulation, contains what 3 components?
streak, pit, and node
The primitive streak and node are essential for what 3 things?
- specifying fates of migrating endoerm and mesoderm
- inducing the nervous system (neural plate)
- defining the rostrocaudal body axis
T/F: During gastrulation, future ectoderm cells move internally via the primitive streak, node and pit, leaving endoderm and mesoderm on the epiblast surface.
False; During gastrulation, future endoderm and mesoderm cells move internally via the primitive streak, node and pit, leaving ectoderm on the epiblast surface.
During gastrulation, presumptive _________ leaves the epiblast first, and replaces the ________ cells to form the embryonic gut. Then, presumptive ______ leaves the epiblast, and invades the space between the ______ and _____, to form muscle and skeleton.
endoderm; hypoblast cells; mesoderm; epiblast; hypoblast/ endoderm
What are the initial 2 germ layers that exist before gastrulation forms the mesoder, ectoderm, and endoderm?
hypoblast; epiblast
Persistant ________ cells are pluripotent (can generate all cell types) and normally disappear at the end of gastrulation via apoptosis. If they don’t, they may result in the individual getting __________.
primitive streak cells; teratomas (i.e. sacrococcygeal teratoma)
NOTE- teratomas removed after birth due to risk of malignancy
At the end of gastrulation, the germ layers are properly arranged, both ________ and _________.
rostrocaudally and dorsoventrally
At the end of gastrulation, the germ layers are properly arranged, both rostrocaudally and dorsoventrally:
1) _____- gut tube, internal epithelia of buccopharyngeal and cloacal membranes
2) ____- notorchord (axial), paraxial, intermdediate and lateral plate mesoderm
3) ____- neural plate and general ectoderm on the surface of the epiblast
1) endoderm
2) mesoderm
3) ectoderm
NOTE- Each germ layer then goes on to produce specific tissues
Each germ layer then goes on to produce specific tissues….. what does the ectoderm, endoderm, and mesoderm eventually form?
Ectoderm- epiderm epithelium (hair, nails tooth enamel), nervous system (PNS/CNS) and neural creast derivatives (pigment cells, tooth dentine)
Endoderm- GI tract epithelium, respiratory tract epitheilium and endocrine glands
Mesoderm- muscle, skeleton, CT, urogenital tract/ germ cells and heart/ blood/ blood vessels
The nervous system is formed from the ectoderm during gastrulation. The ectoderm is divided into what 2 territories? What type of epithelium are they and what do they form?
1) neural plate- columnar epithelium; brain/ spinal cord
2) lateral ectoderm- cuboidal epithelium; epidermis of skin
NOTE- All of the induction of the node occurs at the end of gastrulation
The neural plate is induced to form from the ectoderm by signals from the _____ and from the underlying _______ during gastrulation.
This induction also establishes the ______ axis of the future central nervous system.
node; notochord
rostrocaudal axis
NOTE- All of the induction of the node occurs at the end of gastrulation
What signal is importnat for establishing left-sideness? The dorsal lip of the blastopore (or the node)?
left side- FGF8 (–> Nodal Lefty –> Pitx2)
Dorsal Lip- BMP inhibitor (i.e. Noggin, Chordin, Follistatin)
Neural induction involves embryonic _______, a population of cells that can induce neural cells to form and create ______ axis.
organizers; secondary Body Axis
Embryonic organizers induces neural plate by secretion of ________. What 2 other signals are involved?
BMP inhibitors; IGF and FGF
NOTE- Can get induction of multiple head structures by BMP inhibitors
What signaling induces cranial structures? What loss of function will result in a loss of most cranial head structures?
Wnt Signaling; DKK (a Wnt inhibitor)
NOTE- too much or too little may result in the same phenotype (i.e. too much Wnt signaling/ too little Wnt signaling= loss of head structure)
________, which occurs during week __ of the first trimester, results from the endoerm via cranial/ caudal and bilateral body folding.
Gut Tube Formation; week 4
Cephalo(rostro)-caudal folding occurs in the 4th week. What are anterior changes (5) and posterior changes (2)?
Anterior Changes:
1) forebrain folds ventrally
2) buccopharyngeal (bp) membrane moves posteriorly/ ventrally to the oral region
3) Future heart moves dorsally/ posteriorly to thoracic region
4) amniotic cavity becomes a protective sac wrapped around embryo
5) Forgut forms
Posterior Changes:
1) cloacal membrane moves ventrally/ anteriorly to form future anus
2) hingut forms
Along with cephalo(rostro)-caudal folding, Lateral folding also occurs during week 4, resulting in what?
- fused endoderm
- gut-tube
- smooth muscle
- skin
all at the ventral midline both anterior and posterior to yolk sac. The body wall remains open in the region of the yolk sac until ~week 6
What is gastroschisis and how does it occur?
- occurs when bowel, stomach, and liver are herniated outside the abdominal cavity (closure defects)
- Incomplete lateral body wall folding in weeks 4-5
_________: migration to form muscle, skeleton, dermis, urogenital tract, circulatory system, blood and heart.
Mesoderm development (week 4 of first trimester)
During gastrulation and as the neural tube fuses, the mesodermal subdivisions form. What are the subdivisions from medial to lateral? (4)
notochord, paraxial, intermediate and lateral plate mesoderm
During gastrulation and as the neural tube fuses, the mesodermal subdivisions form:
1) _______: provides axial support until vertebral column forms
2) ______: muscle, bone and dermis
3) ______: urogenital system
4) ______: smooth muscle, heart, blood and vessels, ventral dermis
1) notochord
2) paraxial
3) Intermediate
4) lateral plate mesoderm
Axial, paraxial, intermediate and lateral plate mesoderm each give rise to distinct derivatives.
How is the intervertebral discs formed (4) and what is it?
neural tube > chorda-mesoderm (axial mesoderm) > notochord (serves as embryonic backbone early) > Intervertebral discs
ID- offers structure/ signaling support
Axial, paraxial, intermediate and lateral plate mesoderm each give rise to distinct derivatives
What are the kidneys/ gonads made from?
Intermediate mesoderm
Axial, paraxial, intermediate and lateral plate mesoderm each give rise to distinct derivatives
What is gut smooth muscle, coelom, hear, blood vessels, blood and ventral dermis made from?
lateral plate mesoderm
Axial, paraxial, intermediate and lateral plate mesoderm each give rise to distinct derivatives
What somites do the paraxial mesoderm from into and what do each somite produce?
1) Sclerotome- skeleton
2) myotome- striated/ voluntary muscle
3) dermatome- dorsal dermis of the skin
NOTE- paraxial mesoderm also gives rise to the head
T/F: The paraxial mesoderm doesn’t give rise to the head, along with somites (what somites, 3).
False, gives rise to head
Somites- sclerotome, myotome and dermatome
Anterior mesoderms forms what (2)?
head mesenchyme and prechordal plate
Anterior mesoderm form head mesenchyme and prechordal plate by undergoing _____ together with neural crest cells, which forms craniofacial structures including _______ of the face.
The _______ is a midline structure that contributes to the _______ (it is also importnat signaling center for forebrain).
EMT; muscles
prechordal plate; oropharyngeal membrane
Beginning at neurulation, somites form in the ________, in an anterior to posterior progression. A bilateral pair of somites is added every ___ hours in humans, commencing on day _____. By the end of somitogenesis (end of week __), human embryos have ___ pairs of somites.
paraxial mesoderm; 8 hours; day 21; week 5; 44 pairs
Each somite is partitioned into sclerotome, dermatome, and myotome, which give rise to the skeleton (vertebrate), the dermis, and striated body muscle, respectively. How does this happen?
This occurs via transformation of epithelial cells to a mesenchymal form, to allow migration.
