Early Embryogenesis-Ziermann Flashcards
What are the embryo and fetal weeks respectively?
0-8 weeks is an embryo
8 weeks + is a fetus
During what time can we determine where the head and tail will be?
Week 1-2
By the end of what week do we have a complete human body?
week 8
Week 3-8 consist of what part of embryonic development?
organogenesis
Gameotogenesis requires what two processes?
Meiosis: diploid to haploid
Cytodifferentiation: where the content of the parent cells are distributed to the daughter cells
How is an 80 year old man still able to father a child?
Spermatogenesis begins at puberty and continues through life. It only takes about 3 months to mature.
The epididymis is continually producing sperm cells throughout life
How does oogenesis occur?
Meiosis I occurs during fetal period and it is in dormancy until
After puberty where meiosis I resumes and stops mid-Meiosis II (metaphase II)
Only when a sperm fertilizes an egg (penetrates an egg) does Meiosis II finally complete
How many daughter cells do you produce at the end of spermatogenesis and oogenesis?
spermatogenesis: 4 mature sperm cells
oogenesis: 1 egg and 3 polar bodies
When arrested in metaphase II, mature human ova do not possess a condensed nucleus. True or false?
True
This is the moment in which the chromosomes from the male and female gametes come together within the ovum.
fertilization
sperm has to release chromosomes into the egg
the sperm merely touching the egg does not equal fertilization
Zygotes are __________and contain how many autosomes and sex chromosomes?
sperm +oocyte= zygote
zygotes are 2n so diploid
zygotes contain 46 chromosomes (44 autosomes and 2 sex chromosomes)
When a gamete has 2 or 0 chromosomes, the zygote can have how many chromosomes resulting in what aneuploidies? What is the original cause for the abnormal chromosomal number?
3 or 1
resulting in trisomy or monosomy respectively
due to nondisjunction
Chromosomal anomalies cause about 50% spontaneous abortions.
What is the only trisomy to reach adulthood?
Trisomy 21
Trisomy 13 and 18 children do not live past 1 years old
What are examples of dosage effect chromosomal abnormalities?
Kleinfelter syndrome XXY
Pallister-Killian syndrome : duplication of 12p –> tetrasomy
What are examples of chromosomal abnormalities with deletions?
DiGeorge Syndrome: 22q11.2 deletion syndrome
Cri du chat: deletion on chromosome 5
Fragile X syndrome
Angelman Syndrome
Prader-Willi syndrome
This occurs when a gene is active depending on whether it came from the father or mother.
genetic imprinting
Why does incidence of nondisjunction increase with the age of the mother?
the mature ova stuck in metaphase II, has to be pulled apart by microtubules which get weaker over time
Structural defects occur in what stage of meiosis normally?
meiosis I
Why does incidence of structural defects increase with the age of either parent?
due to environmental factors, examples include:
- stress
- overconsumption of vitamins
What time period are developing embryos most susceptible to malformations?
the first 8 weeks of embryogenesis
are when most malformations occur
What are teratogens? Give examples
an agent or factor that causes malformation of an embryo
pharmaceutical treatments: abx, anticoagulants, anticonvulsants, antitumor agents, sedatives, tranquilizers, some hormones, excess vitamin A (retinoic acid)
teratogenesis: is the process by which congenutal malformations are produced in an embryo or fetus
1/3 to 1/2 of all conceptions end in spontaneous abortions (miscarriages)
1/4 of these abortions occur before pregnant is detected
True or false?
TRUE!
In placental mammals, you need how many genetic sets to form a normal embryo?
You need 2 genetic sets: one from mother and one from father
You 2 genetics sets in total that come from BOTH mother and father
Gene for insulin-like growth factor, which favors growth is inherited from the _________.
Gene for growth factor receptors, which neutralize the growth factors and limit growth are inherited from the _________.
This is why it is necessary for 2 genetic set to come from BOTH parents.
father
mother
Epigenetics can influence generations after. True or false?
TRUEEEE
In 1940-50s, people were exposed to DDT. In animals exposed to DTT, 1/2 of the 4th generation offspring were obese, despite the 2nd generation being of normal weight.
Dithiothreitol (DTT)
What is the first time in which we’re able to differentiate between the outer (ectoderm) and the inner cells (embryo)?
morula which is a result of the cleavage process of the zygote
What structure in embryogenesis, will become the human and the placenta?
blastocyst where the inner part will become the human and the outer part will become the placenta
Fertilization, cleavage, and implantation occurs during which week of embryogenesis?
Week 1
Where does fertilization occur? What if it occurs elsewhere?
the ampulla of the uterine tube
fertilization occurs in the fallopian tubes
if it occurs elsewhere you can get ectopic pregnancy and potential harm to the mother as well
What are the 4 events that lead to fertilization?
- capacitation
- acrosome reaction: release of enzymes
- fusion of germ cell plasma membranes: sperm melts its membrane with the membrane of the egg
- cortical reaction: resulting in no other sperm cell being able to enter the ovum (a SLOW block to polyspermy)
Describe the last step of maturation for sperm.
Capacitation
glycoprotein coat important for sperm to get through the hostile vaginal environment is lost within the uterine tube thus exposing the acrosome
FUN FACT:
Out of 300 million sperm deposited, ~300 make it to the ampulla of the uterine tube. 10% abnormal
What contains the enzymes necessary to penetrate the zona pellucida of the egg?
Zone pellucida is the jelly coat of the oocyte made up of a TOUGH glycoprotein shell
acrosome of the sperm
What is the last step of oocyte meiosis AKA oogenesis?
fertilization
remember metaphase II is completed after fertilization of oocyte with sperm
What results in FAST block of polyspermy?
During contact and fusion of the sperm and egg membranes, a hole is made in the vitelline layer. This allows contact and fusion of the gamete plasma membranes. The membrane becomes depolarized, resulting in the fast block to polyspermy?
What results in SLOW block of polyspermy?
the cortical reaction
Fusion of the gamete membranes triggers an increase of Ca2+ in the egg’s cytosol, causing cortical granules in the egg to fuse with the plasma membrane and discharge their contents. This leads to swelling of the perivitelline space, hardening of the vitelline layer, and clipping of sperm-binding receptors. The resulting fertilization envelope is the SLOW block to polyspermy.
Where do our mitochondria originate?
from our mother
all sperm mitochondria degenerate and thus all mitochondria in the human body are of maternal origin
this is used in ancestry as iti easier to follow a maternal lineage as opposed to a paternal lineage
State this process.
each pronucleus doubles its DNA —> all chromosomes line up on a single mitotic spindle, then each duplicated chromosome splits to form 2 identical diploid cells
the 1st cleavage of the zygote
remember from here on out everything is DIPLOID
Cell of what embryological structure consists of tight junctions between outer cells and gap junctions between inner cells to allow for flow of intercellular communication.?
morula
this is the first time we see differentiation of cells
different environments–different fates
After differentiation, the outer cells can still become an inner cell. True or false?
FALLLSSEEE
Every cell is totipotent or even omnipotent and capable of making a complete human or placenta BEFORE differentiation.
AFTER differentiation cells are now pluripotent as they are already expressing genes to become whatever that they’ve been assigned to become.
Transcriptions factors being able to mediate the expression of gene is an example of?
epigenetics
TF bind to specific regulatory areas of the genome, to promote or inhibit transcription
So the identity of the DNA base pairs does not change
In the morula we have ________cells and the blastocyst we have _________cells.
totipotent in the morula where there is 12-32 blastomeres; morula is still enclosed by the zona pellucida
pluripotent in the blastocyst which hatches from the zona pellucida; outer cell becomes the trophoblast (embryonic placenta) and embryoblast becomes the human; fluid is pumped in to form an internal blastocyst cavity
What is the source of embryonic stem cells?
the embryoblast of the blastocyst
The process of implantation starts with what embryological structure?
blastocyst
Day 5: blastocyst floats in the uterine wall
Day 6: blastocyst adheres to the intrauterine wall
Day 7: implantations begins as the trophoblast invades into the uterine wall
Cells of the trophoblast of the blastocyst differentiate into 2 layers:
__________which is the layer of highly mitotic cells, enclosing the blastocyst
_____________which are cells that fuse into multinucleated mass and produce proteolytic enzymes to aid their invasion of the uterine wall
cytotrophoblast: highly mitotic cells
syncytiotrophoblast: forms multinucleated mass
Fertilization should occur at the beginning of the fallopian tube (the ampula of the uterine wall). 54% of ectopic pregnancies occur in the ampular tubal. Most ectopic pregnancies can lead to severe hemorrhaging in women and termination of pregnancy? Why is implantation in areas other than the uterine wall more dangerous?
Uterine wall can only accept implantation days 6-8. Other organs can accept anytime!
These other organs do have have the space, capacity, or resources to grow a normal baby and once again a major risk is posed to the mom.
What stage of the embryogenesis are monozygotic twins commonly made?
division of the inner cell mass of blastocyst causing separate amnions, single chorion and placenta (most common)
- division could also occur between 2-cell and morula stages to produce identical blastocysts resulting in separate amniotic and chorionic sacs and either separate or fused placentas
- embryonic disc splits up (very rare)
anything before the morula can divide and make another baby
Our original germ cells are diploid but we go through this process that requires meiosis to produce haploid gametes.
Gameotogenesis
What are conjoined (siamese) twins?
twins that are conjoined due to imcomplete division of the inner cell mass or embryonic during twinning process.
How are fraternal twins made (AKA paternal twins)?
2 eggs are fertilized by 2 sperms
these fertilization may even be in two different menstrual cycles
the right and left ovary mature at different time points
Should C-sections for convenience be discouraged?
YYYEESSS!!!!!
you’re baby is immediately delayed in its immune system if it is not born through the vaginal canal
What is placental accreta?
The implantation occurs where the uterine wall is deficient such as a cesarean scar. Excessive invasion occurs as a result.
During the birth process, you first birth the baby, then you birth the placenta.
In this condition, the placenta cannot detach normally at birth causing severe hemorrhaging in the mother.
The incidence of this occurring is very high with a history of cesarean sections.
What occurs in week 2 of the embryonic development?
-completion of implantation
followed by development of placenta
-formation of bilaminar embryonic disc
Day 9: implantation continues; inner cell mass forms bilaminar disc
Day 11: implantation complete; amniotic sac and yolk sac form
The intervillous lacuna has the maternal blood flowing. What is the connection between the cytotrophoblast, syncytiotrophoblast, and mesoderm that ensures the gas exchange between maternal and embryonic tissue?
chorion = cytotrophoblast + syncytiotrophoblast
the chorion is what becomes the embryonic portion of the placenta
What is the ONLY connection of the free-floating embryo with the mother during Week 2 of pre-natal development?
the connecting stalk or body stalk
it contains the umbilical blood vessel
the yolk sac becomes separated from the cytotrophoblast by the chorionic cavity
What produces the hormone human chorionic gonadotropin (hCG) that forms preserves the uterine lining (on your period you’re shedding the uterine lining) and forms the basis of pregnancy tests?
the syncytiotrophoblast in the chorion
How does the mother ensure not to reject the baby with an immune response?
through the hCG
it inhibits the immune system of the mom to not reject the embryo
syncytiotrophoblast lack the usual cell surface antigens and thus are invisible to the mother’s immune system
The mother’s immune system switch from which immunities to help her tolerate her pregnancy?
switch from cell-mediated immunity to humoral (antibody) immunity
during this time there is increased change of infections, IMPROVEMENT of symptoms of autoimmune disease cell-mediated like rheumatoid arthritis and multiple sclerosis, and WORSENING of auto-immune diseases antibody mediated like systemic lupus erythematous
During Day 8 of pre-natal development, the embryoblast segregates into two layer:
_________which forms the fluid-filled cavity that will become the amniotic sac cavity; all its cell will form the layers of the embryo (become the human body)
_______which will form the yolk sac
epiblast
hypoblast
What is the source of the first embryonic blood cells and of primordial germ cells?
the yolk sac
