Bilaminar Embryo (week 2) Flashcards
what are the two forms of trophoblast during week 2 (bilaminar embryo)
Trophoblast: cytotrophoblast & syncytiotrophoblast
what are the two blastocoele transformations during week 2 (bilaminar embryo)
Blastocoele transformations: to primary yolk sac & to secondary yolk sac
what are the two cavities that form during week 2 (bilaminar embryo)
Cavities: Amniotic & chorionic
what placental (chorionic) villi are formed during week 2 (bilaminar embro)?
Chorionic Villi (placental): primary & secondary villi
which pole (dorsal or ventral) invades the endometrium first?
dorsal
how many days after fertilization does implantation occur? what are the two stages of implantation?
occurs 6-8 days after fertilization; 2 stages = attachment and invasion
what are the two stages of attachment?
- apposition
2. adhesion
What happens during the apposition stage of attachment?
it is the first stage of attachment; the blastocyst forms an unstable interaction with the uterine wall via interdigitation between pinopodes (uterine epithelium) and microvilli (blastocyst surface)
During apposition, the blastocyst forms an unstable interaction with the uterine wall via ________ on the uterine epithelium and __________ on the blastocyst
pinopodes (uterine epithelium); microvilli (on the blastocyst)
What happens during the adhesion stage of attachment?
second stage of attachment; increased physical contact between the animal pole of the blastocyst and the uterine epithelium (more stable binding) via specific integrin receptors and components of the ECM
what facilitates the more stable attachment of the blastocyst to the uterine epithelium during adhesion stage?
specific integrin receptor that bind to extracellular matrix components that are produced by trophoblast and the uterine wall
During Invasion, the trophoblast cells differentiate into mononuclear ______ and mulitnuclear ________.
cytotrophoblast and synctiotrophonblast
what penetrates through the uterine eptithelium first, synctiotrophoblast or cytotrophoblast?
synctiotrophoblast first, followed by cytotrophoblast and the rest of the blastocyst
what facilitates the penetration of the blastocyst through the uterine epithelium and into the endometrium? how?
the synctiotrophoblast secretes matrix metalloproteinase (MMPs) which degrade components of the basement membrane and EXM
what generally occurs during invasion?
- Synctotrophoblast penetrates uterine epithelium preceded by retraction of epithelium cells
- Synctotrophoblast breaches the basement membrane
- Invasion of endometrium by Synctotrophoblast (via release of MMPs) followed by the rest of blastocyst
what happens to the embryoblast cells as soon as the blastocyst begins to invade the endometrium?
the embryoblast cells (inner cell mass) begin to proliferate and differentiate, separating into two distinct layers: hypoblast and epiblast
what two cell layers does the embryoblast divide into? What are their respective locations
hypoblast– cell layer facing blastocyst cavity
epiblast – cell layer adjacent to the trophoblast
What is the amnionic cavity formed by?
cavitation of the epiblast
what cells line the amnionic cavity on the side adjacent to the hypoblast?
epiblast
what cells line the amnionic cavity on the side adjacent to the trophoblast?
aminoblasts
what is the bilaminar embryo?
2 adjacent flat disks formed by the epiblast and hypoblast
what does the trophoblast give rise to?
nothing! it is terminally differentiated tissue (cant turn into anything else but trophoblast cells)
what does the inner cell mass give rise to?
everything! it is pluripotent and splits into the hypoblast and epiblast
what do the hypoblast and amnioblast cells give rise to?
only extraembryonic tissues
what do the epiblasts give rise to?
all tissues and organs of the embryo
What cells gives rise to the exocoelomic (Heuser) membrane?
hypoblast cells
what lines the primitive yolk sac?
exocoelomic (Heuser) membrane
What is the extraembryonic mesoderm formed by?
hypoblast cells that migrated into the space between the Heuser membrane and trophoblast and they transdifferntiated into mesenchymal cells
what are extraembryonic coelom? where are they found? what is its function?
aka “chorionic cavity” ;
lacunae that form within the extraembryonic mesoderm and that gradually become larger; function is to split the extraembryonic mesoderm into two layers (splanchnopleuric and somatopleuric)
what are the two layers of the extraembryonic mesoderm? what does each layer cover?
- splanchnopleuric mesoderm (covers the yolk sac)
2. somatopleuric mesoderm (lines the trophoblast and amnionic cavity)
What is the external lining of the primitive yolk sac? the internal lining?
external: extraembryonic mesoderm
internal: Heuser’s membrane
What forms from the second wave of proliferating and differentiating hypoblast cells?
extraembryonic endoderm; displacing the primitive yolk sac and form a much smaller secondary/definitive yolk sac
what do the remnants of the primitive yolk sac become?
exocoelomic cysts
what is the internal lining of the secondary yolk sac? what is the external lining?
internal: extraembryonic endoderm (second wave hypoblast)
external: splanchnopleuric mesoderm
what forms the chorionic plate?
somaptopleuric mesoderm with adjacent cytotrophoblast
what is the only place where the embryo remains to be attached to the chorionic plate?
connecting stalk
what is the connecting stalk?
a mass of extraembryonic mesoderm that is the only place where embryo remains to be attached to the chorioinic plate
why is it necessary that the embryo establish a communication with maternal blood supply?
because mammalian embryos require an external source of nutrients to grow and develop
How does the embryo begin to establish a communication with maternal blood?
the synctiotrophoblast begin to engulf maternal endometrial capillaries and the maternal blood fills the trophoblastic lacunae creating an anastomotic network of blood filled spaces within the synctiotrophoblast. The lacunar blood then comes into contact with the placental (chorionic) villi and provides an interface between the embryo and maternal blood circulation
what are the placental (chorionic) villi formed from?
cytotrophoblast forming cellular columnar structures and then transforming into 4 diff types of villi
what are primary villi characterized by? What day post-fertilization are they usually present?
cellular columns of cytotrophoblasts
days 11-13
what are secondary villi characterized by? What day post-fertilization are they usually present?
primary villi + mesenchymal core
day 16-17
what are tertiary villi characterized by? What day post-fertilization are they usually present?
secondary villi + blood capillaries that differentiate into blood vessels that connect up with embryonic blood vessels later in development
day 21
when is the primitive placenta established?
by the end of the third week of gestation (with the formation of the tertiary villi)
What is an early spontaneous abortion (ESA)?
a pregnancy that is lost during the first 3 weeks after fertilization ; random and usually represents natural selection; usually goes undetected
what is a recurrent spontaneous abortion (RSA)
3+ consecutive pregnancy losses before the 20th week of gestation
what is recurrent spontaneous abortion caused by?
- genetic anomalies
- anatomical anomalies
- endocrine factors
- immunological factors
- infections
- smoking, alcohol consumption, and other environmental factors
What type of genetic anomalies are common in recurrent spontaneous abortion?
usually there is a normal karyotype (genome), with triploidy or tetraploidy of sex hormones, or monosomy of X chromosome
what is an ectopic pregnancy?
pregnancy resulting from embryo implantation outside the normal sites in the uterus (usually in the fallopian tube or peritoneal cavity)
what are the main causes of ectopic pregnancy?
- infection (gonorrhea, chlamydia)
- inflammation (pelvic inflammatory disease.. from STDs)
- scar tissue from previous abdominal or fallopian surgeries
- abnormal fallopian tube development
what are the symptoms and treatment of ectopic pregnancy?
symptoms: severe abdominal pain in pregnant women, severe internal bleeding
treatment: surgical removal of ectopic embryo
What is a complete hydaidiform mole (CHM)
- human conceptus that develops into a disorganized mass of placental derivatives (fetus is absent)
- 2 sets of chromosomes solely of paternal origin (no expression of maternally expressed imprinted genes)
- normal embryo cannot develop, but trophoblast can develop, do the fetus does not develop at all and conceptus is comprised solely of the trophoblast
where does CHM usually occur? why?
in the trophoblast because expression of maternally expressed imprinted genes is not required for trophoblast development and funciton, but both maternal and paternal expressed imprinted genes are necessary for normal embryo development
what are imprinted genes?
genes that are only expressed from the maternal or paternal copy of the chromosome
what is placenta previa?
an obstetric complication in which the placenta is inserted partially or wholly in lower uterine segment\
Four stages: I-IV, where I is placenta in lower segment and does not cover the internal os –> complete covering of cervix)
What is Recurrent biparental mole (BiCHM)
both maternal and paternal chromosomes are present, but no expression of maternally imprinted genes
What are some of the symptoms presend with CHM?
- vaginal bleeding toward the end of the first trimester
- ultrasound reveals the absence of a fetus
- hCG levels become excessive early in pregnancy
What is choriocarcinoma?
aggressive cancer that represents a highly vascularized malignant transformation of a trophoblast; characterized by early spread of metastasis to the lungs
what are the clinical signs of choriocarcinoma?
- excessive levels of hCG
- vaginal bleeding
- chest pain
- coughing up blood
- shortness of breath
- chest x-ray showing multiple infiltrates of various shapes in both lungs
How is choriocarcinoma treated?
surgical removal; the level of hCG must be checked after the surgery to ensure eradication; or chemotherapy with methotrexate
