The Second Week (Exam 1) Flashcards
What are the rule of 2’s seen during the second week
2 embryonic layers each form 2 layers
2 cavities are formed
What are the two layers of cells that start the second week
Trophoblast
Embryoblast
What does the trophoblast give rise to
syncytiotrophoblast
cytotrophoblast
What does the embryoblast give rise to
hypoblast
epiblast
What is the syncytiotrophoblast
multinucleated blob that secretes hCG
What is the cytotrophoblast
invades the uterus, very cellular
What is the epiblast
primordial germ cells that will form all embryonic tissues
What two cavities form during the second week
amniotic cavity
yolk sac
What are the sources of amniotic fluid
mother: leaky capillary beds in the placenta
Fetus: Urine
What is polyhydraminos
too much amniotic fluid
What is oligohydraminos
too little amniotic fluid
What clinical problems may lead to polyhydraminos
swallowing defects, GI issue, digestive congenital anomaly
What clinical problems may lead to oligohydraminos
no external genitalia
What are the contents of the amniotic fluid
fetal cells alpha-fetoprotein Acetylcholinesterase pulmonary phospholipids/lamellar bodies infections
What might high levels of alpha-fetoprotein indicate
body wall defect
What is the yolk sac formed from
hypoblast
Describe the lining of the primitive yolk sac
hypoblast that lines is now called extraembryonic endoderm
What is the entire lining of the yolk sac called
heuser’s membrane
Where is the extraembryonic reticulum secreted
between extraembryonic endoderm and the cytotrophoblast
What does the extraembryonic reticulum do
separate yolk sac and embryoblast from the trophoblast
What are the two layers of the extraembryonic mesoderm
Somatopleuric
Splanchnopleuric
What is the somatopleuric layer of the extraembryonic mesoderm in contact with
trophoblast
What is the splanchnopleuric layer of the extraembryonic mesoderm in contact with
embryo
What is the chorionic cavity surrounded by
extraembryonic mesoderm
What type of cells will be formed from extraembryonic mesoderm
primordial placenta cells as it is outside of the embryo
When is the yolk sac classified as secondary
when exocoelomic cyst splits off it is considered secondary
What will the syncytiotrophoblast do
invade uterus epithelium and secretes hCG
What will cytotrophast do
continue to proliferate
What is secreted by the cytotrophoblast
enzymes that break down ECM of endometrial cells
What subunit of hCG is unique
Beta subunit
When can beta hCG be detected
6-8 days after ovulation
What is negative beta hCG <5 mlU/mL
<5 mlU/mL
What is positive beta hCG
> 25mIU/mL
How many days does it take for hCG to double
every 2.2 days
How will hCG levels differ in patients who’s pregnancies are destined to abort
they decrease or do not develop as fast
When will there be increased levels of hCG
molar pregnancies pregnancy choriocarcinoma germ cell tumors hepatoma lymphoma
How will hCG be in ectopic pregnancies
lower range
Situations in which there would be a decreased level of hCG
indicative of decreased viability of the placenta
risk of spontaneous abortion dead fetus
What will happen within the trophoblast around day 9
uteroplacental circulation begins to form
What forms the start of uteroplacental circulation
spaces begin to form within the syncytiotrophoblast
What are the spaces of the syncytiotrophoblast at the start of uteroplacental circulation called
trophoblastic lacunae
What occurs at the same time as trophoblastic lacunae formation
maternal capillaries near the syncytiotrophoblast begin to expand
What are the expanded capillaries near the syncytiotrophoblast called
maternal sinusoids
What do the maternal sinusoids do after being formed
join the trophoblastic lacunae (maternal blood fills the lacunae)
When do primary stem villi form
between days 11-13
What are primary stem villi
cytotrophoblast proliferates and forms extensions that extend into the syncytiotrophoblast that extend into the blood filled lacunae
Primary stem villi are the first steps in forming what
fetal arteries and veins
What are the layers of the primary stem villi
cytotrophoblast (inner)
syncytiotrophoblast (outside)
When are secondary stem villi formed
day 16
What are secondary stem villi
extraembryonic mesoderm extends into primary villi
When are tertiary stem villi formed
End of the third week
What is a tertiary stem villi
villus has formed new blood vessels that connect to forming fetal blood vessels
What occurs on Day 6
implantation
What occurs on Day 16
gastrulation
What occurs on Day 18
neural plate forms
What occurs on day 20
first somite forms
What occurs on Day 22
neural tube begins to close and heart begins to beat
What occurs on day 24
thyroid gland begins to form
What occurs on Day 24-25
cranial neuropore closes
What occurs on day 26-27
caudal neuropore closes
What occurs on week 2
primordial germ cells arise from the epiblast
What occurs on week 3
primordial germ cells in the yolk sac
What occurs on Week 4
pharyngeal arches form
What occurs on week 6
primordial germ cells arrive at genital ridge/ midgut herniation
What occurs on week 9
external genitalia can be distinguished/ liver begins blood formation
What occurs on week 10
return of midgut
What occurs on week 12
blood formation involves spleen
What occurs on week 30
blood formation shifts to marrow
What is the embryonic part of the placenta
tertiary stem villi
What is the function of the tertiary stem villi
route for exchange and diffusion
What layers will INITIALLY need to be transversed in a tertiary villi for exchange between mother and fetus
cytotrophoblast
syncytiotrophoblast
CT/ECM of villus
Endothelium of embryonic vessels
What layers will need to be transversed over time in a tertialry villi
the syncytiotrophoblast
What occurs over time to the tertiary villi
fetal blood vessels get closer to wall of syncytiotrophoblast and cytotrophoblast is dispersed
What is the chorion composed of
syncytiotrophoblast
cytotrophoblast
extraembryonic membrane
What is the function of the chorion
help form placenta
How do genomic imprinting of maternal and paternal genome affect blastocyst formation
Maternal genome plays a role in eMbryonic development
Pateral genome plays a role in troPhoblast development (Placental)
What symptoms occur with hydatidiform mole
high hCG hypertension bleeding uterus enlargement greater than expected theca lutein cysts
What is hydatidiform mole
placenta without an embryo
What are the two proposed mechanisms for molar pregnancy
fertilization of an empty occyte with duplication
fertilization of an oocyte by two sperms
What is complete molar pregnancy
cystic swelling that arises from development of trophoblast without an embryoblast
What is partial molar pregnancy
poorly developed embryo
What genome does a partial molar pregnancy have
triploid (XXX or XXY)
What causes partial molar pregnancy
2 sperm fertilized a normal ovum
What type of cancer is associated with molar pregnancy
choriocarcinomas
Where do choriocarcinomas often metastasize
to the lungs and requires chest scans
What is a hydropic chorionic villi
fluid filled villi associated with molar pregnancy; no embryo to drain the spaces so fluid builds up
can be seen on US
Key signs and symptoms of molar pregnancy
bleeding lower abdominal pain pre-eclampsia before 24 weeks uterus large for dates absent fetal hear sounds, no fetal parts on US Expulsion of "grape-like" vesicles
What diagnostic studies are used in molar pregnancies
beta hCG (elevated)
US
Chest films: rule out choriocarcinomas
When the blastocyst has a endoblast and hypoblast, what is the embryo referred to as
bilaminar germ disc
The amniotic cavity forms
between the epiblast cells
Where does the chorionic cavity form from
the extraembryonic mesoderm
With the chorionic cavity, the extraembryonic mesoderm is divided into what
two layers:
splanchnopleuric
somatopleuric
Where does the somatopleuric layer go
lines the cytotrophoblast
What does the somatopleuric layer do
help form the chorion
Where does the splanchnopleuric layer go
in contact with germ disk
What does the splanchnopleuric layer contribute to
umbilical cord
The chorion helps form what
the placenta
What is the chorion composed of
somatopleuric layer of extraembryonic mesoderm
cytotrophoblast
syncytiotrophoblast
90% of complete moles are what
46, XX
In origin, what are complete moles genetically
paternal
What percentage of moles go on to form choriocarcinomas
5%
Where do choriocarcinomas metastasize to
brain, bone, and lungs
