Embryogenesis Flashcards
match with week 1 or week 2 of prenatal development:
placenta formation
trophoblast differentiation
blastocyst formation and implantation
embryoblast differentiation
fertilization
week 1: fertilization, blastocyst formation/implantation
week 2: embryoblast differentiation, trophoblast differentiation, placenta formation
when does an embryo become a fetus?
embryogenesis: week 1-2
embryonic period: week 3-8
fetal period: week 9-38
during what period of prenatal development (name of period and weeks) is there higher teratogen susceptibility
embryonic period: week 3-8
contrast ovulation vs capacitation, preparatory processes for fertilization
ovulation: oocyte discharges from ovary and migrates into uterine tube (day 14 of 28 day cycle)
capacitation: spermatozoa conditioned in the female tract to be able to fertilize the oocyte
describe each of these steps briefly:
1. ovulation
2. fertilization
3. proliferation
4. implantation
- ovulation: oocyte leaves ovary and migrates into uterine tube, ovary secretes hormones to prepare uterine lining for implantation
- fertilization: occurs in ampulla - sperm can live for several days, unfertilized oocyte degenerates within a day
- proliferation: cleavage occurs as embryo migrates through uterine tube to uterus
- implantation: blastocyst embryo implants into uterine wall by end of 1st week
where does fertilization occur
ampulla: widening at end of uterine tube
what form is fertilized oocyte in when it implants?
blastocyst embryo
what are the shell layers of the oocyte and function
- corona radiata: (aka cumulus oophorus) outermost, follicular cells, protection/energy/support, chemoattractants for sperm
- zona pellucida: intermediate glycoprotein layer (zona proteins, ZP) - ZP3 binds sperm
- plasma membrane
this intermediate glycoprotein layer of the oocyte shell contains ZP3 protein that binds sperm. What is?
zona pellucida
Hint: ZP3 protien = Zona Pellucida 3
this shell of oocyte provides energy and support for oocyte
outermost corona radiata (aka cumulus oophorus)
what sperm modifications take place during capacitation?
glycoproteins removed at tip to make membrane overlying acrosome more fluid for enzyme release
intracelular signaling modifications
sperm tails become hyper-activated for more motility
how does penetration of each oocyte shell take place (phases of fertilization)?
- sperm penetrates corona radiata via whipping its tail
- sperm penetrates zona pellucida via binding ZP3 and releasing acrosomal enzymes
- oocyte and sperm PM fuse and oocyte meiosis II is completed - gametes fuse their haploid (n) pronuclear to form diploid (2n) zygote
what important processes block polyspermy?
- oocyte PM depolarizes to prevent further entry
- intracelular Ca2+ wave
2a. cortisol reaction: exocytosis of lysosomal enzymes from cortical granules
2b. zona reaction: zona pellucida becomes impenetrable (middle layer)
formation of dizygotic vs monozygotic cells
dizygotic: 2 oocyte are ovulated and each is fertilized. amniotic cavities are separate, placentas may be shared or separate
monozygotic: single oocyte is fertilized by single sperm, but zygote splits into 2 zygotes in the first week. timing of split determines if amniotic cavities and placentas will be separate or shared (earlier = independent)
blastomeres
end product of cleavage division (symmetrical mitotic cell divisions during week 1) up through 8-cell stage
blastomeres are smaller cells with each successive division and are encased by zona pellucida in early embryo (they’re all squeezing in)
totipotent cells (can be embryonic and extraembryonic tissue)
this occurs while embryo migrates through oviduct to uterus
dividing embryonic cells are considered blastomeres up through the ____ cell stage and their potency is ___ during this time
blastomeres up through 8-cell stage
these cells are totipotent
morula - when and what
32-cell morula develops by day 4
solid ball of compacted cells migrating in uterine tube toward uterus (following blastomere cleavage division)
cells within segregate and establish polarity: inner cell mass (ICM) is embryoblast, outer cell mass (OCM) is trophoblast (placenta)
embryoblast vs trophoblast
embryoblast is inner cell mass of morula
trophoblast is outer cell mass of morula - becomes placenta
when does blastocyst form and what is it and how
fluid from uterine cavity penetrates zona pellucida and surrounds cells of morula’s embryoblast (ICM)
4.5 days of fertilization - penetrating fluid pools to form blastocyst cavity of newly formed BLASTOCYST
so group of cells is blastocyst once the fluid comes in to separate ICM from OCM
what form of cells have greatest clinical potential as embryonic stem cells (ES cells)?
pluripotent embryoblast/ICM cells
can give rise to anything but not placenta
when does blastocyst implantation occur and what is this phase called
blastocyst (formed after uterine fluid separates ICM and OCM of morula) implants around day SIX
this is during the SECRETORY phase of endometrium (day 20 of 28 day cycle)
pregnant endometrium undergoes decidua reaction - becomes more secretory
decidua reaction
pregnant endometrium becomes more secretory following implantation of blastocyst (6 days after fertilization)
implantation occurs during secretory phase
what cells are needed to drive blastocyst implantation and what do they do?
trophoblasts: at embryonic pole of blastocyst, secrete enzymes that degrade zona pellucida to allow “hatching” through it and implantation into secretory endometrium
trophoblasts embed into uterine wall to form fetal components of the placenta
secrete hCG (human chorionic gonadotropin) to induce continued ovary secretion of progesterone for endometrium maintenance
trophoblasts secrete ___ to induce continued ovary secretion of ___
trophoblasts secrete hCG to induce continued ovary secretion of PROGESTERONE
this happens following embedding into uterine wall
trophoblasts eventually form fetal components of placenta
role of hCG and when it can be detected in blood and urine
maintains hormone secretion by the ovary to support early pregnancy
detectable in blood 1 week after conception
detectable in urine 2 weeks after conception (home pregnancy test)
elevated in pregnancies with multiple embryos, depressed in some diseases
gestational trophoblast disease
cancer of trophoblasts which normally form the placenta
can occur with or without surviving fetus
where do most ectopic pregnancies occur
uterine tube (ampulla - wide opening of uterine tube)
*may be clinically mistaken for appendicitis
during week 2, embryoblasts of blastocyst form 2-layered ____
bilaminar disc - forms via embryoblast differentiation
epiblast on one side (closer to uterine wall - amniotic cavity), hypoblast on other side (yolk sac)
epiblasts of the bilaminar disc differentiate into cells of embryo proper and _____
amnioblasts
amniotic cavity is initially dorsal to bilaminar disc (on the side closest to the uterine wall) but expands to surround the embryo
what is the main source of amniotic fluid
fetal urine (mostly water)
polyhydramnios vs oligohydramnios
polyhydramnios: excess amniotic fluid
oligohydramnios: insufficient amniotic fluid
inability of a fetus to swallow, esophageal-duodenal atresia, and anencephaly might cause….
polyhydramnios: excess amniotic fluid
the yolk sac is made of ____ (cells) and is [ventral/dorsal] to bilaminar disc initially?
yolk sac: made of proliferating hypoblasts lining the inner trophoblast surface of blastocyst cavity
ventral to bilaminar disc before eventually regressing (farther form uterine wall than amniotic cavity)
early exchange, hematopoiesis, germ cells to gonads
what cells give rise to connecting stalk?
hypoblasts (found in yolk sac, ventral to bilaminar disc initially)
connecting stalk eventually becomes umbilical cord
what forms the fetal and maternal part of the placenta, respectively?
fetal part: trophoblasts (cells that implant into endometrium)
maternal part: develops from trophoblast-altered endometrium
what are the fetal and maternal parts of the placenta called, respectively?
fetal part: chorion frondosum (trophoblasts and hypoblasts)
maternal part: decidua basalis (uterine endometrium)
what cells make up the chorion frondosum, the fetal part of the placenta?
trophoblasts and hypoblasts
how does uteroplacental circulation work? (what are the components)
2 umbilical arteries carry fetal blood from fetus to placenta
1 umbilical vein carries fetal blood to fetal body from placenta
————————
spinal arteries carry maternal blood with nutrient supply to placenta
uterine veins carry maternal blood with waste away from placenta
the germ layers (ectoderm, mesoderm, endoderm) form from what cell mass
epiblast
(embryoblast —> epiblast and hypoblast)
germ layers form during week 3
during week 3, epiblast of bilaminar embryo forms 3-layer _____ disc in process called _____
trilaminar disc forms in process called gastrulation (ectoderm, mesoderm, endoderm)
ectoderm, mesoderm, and endoderm ALL originate from the ____
epiblast
gastrulation begins with formation of _____ in epiblast of bilaminar disc at ____ end
primitive streak in epiblast at CAUDAL end
what is the process of gastrulation
epiblast cells migrate to primitive streak (caudal end) where they detach and invaginate through primitive streak
invaginated epiblasts migrate to form trilaminar disc
epiblast cells displacing hypoblast cells become ENDODERM
epiblast cells between endoderm and epiblast form MESODERM (migrate laterally and cranially)
those left behind are ECTODERM
polarity of embryo is established during ___
gastrulation
during gastrulation, epiblast cells that displace hypoblasts form ____
epiblast cells that settle in the middle and migrate laterally and cranially form ____
leftovers are ____
during gastrulation, epiblast cells that displace hypoblasts form ENDODERM
epiblast cells that settle in the middle and migrate laterally and cranially form MESODERM
leftovers are ECTODERM
what are the general fates of the 3 germ layers
ectoderm: communication with external environment (nervous system, epidermis, sensory receptors, some glands)
mesoderm: support through muscles and connective tissue (skeletal, muscular, urogenital, cardio)
endoderm: digesting, breathing, secreting (many glands, epithelia of urinary bladder, GI respiratory systems)
epiblast ____ create molecular gradients that result in asymmetry/sidedness in signaling cascades and expression patterns to establish polarity
epiblast CILIA - beat right-to-left
polarity:
cranial-caudal
dorsal-ventral
right-left
*abnormal cilia associated with reversed organs, respiratory and fertility issues
buccopharyngeal and cloacal membranes
buccopharyngeal membrane: at cranial end of embryo, future location between oral cavity and pharynx
cloacal membrane: at caudal end of embryo, future location of anus
*both are sites where ectoderm and endoderm adhere tightly without migration of intervening mesoderm
when does primitive streak regress
end of week 3
*teratomas form when primitive streak fails to regress and contain multiple tissues derived from pluripotent epiblast cells
nervous system, epidermis, and some glands are formed from which germ layer
ectoderm
urinary bladder epithelia and GI and respiratory system develops form which germ layer
endoderm (also glands)
urogenital and cardio system form from which germ layer
mesoderm (also skeletal, muscular)
when does organogenesis occur
weeks 3-8 during embryonic period - formation of all organs and tissues of body
*this period is highly susceptible to teratogens
ultrasound of a pregnant woman shows 2 separate amniotic cavities and 1 shared placenta. What must this be?
fraternal twins - separate amniotic cavities, shared OR separate placenta
Which of these occurs during week 3 of embryogenesis?
a. formation of digestive system
b. initiation of extraembryonic mesoderm formation
c. regression of yolk sac
d. amniotic cavity formation
e. formation of three primary germ layers
week 3: formation of 3 primary germ layers - form through epiblast migration at the primitive streak
oxygenated and nutrient-rich fetal blood flows through the _____
umbilical vein
gas exchange between mother and fetus occurs at ____
placenta interface
*no mixing of metal and fetal blood
oxygenated maternal blood coming from uterine spiral arteries bathes external surfaces of villi of the placenta and the fetal blood goes through capillaries inside the villi
