Bilaminar Embryo Flashcards
The secondary oocyte is surrounded by
Zona pellucida and Corona radiata
A think transparent gelatinous layer of protein and polysaccharides
Zona Pellucida
Several layers of ovarian follicle
Corona radiata
Sperm must penetrate what in order for fertilization to occur
Zona pellucida and Corona radiata
What is capacitation
function changes that sperm undergo in the female reproductive tract that enable them to fertilize a secondary oocyte
Capacitation increases what
sperm motility
What is the acrosome and what is its function
modified lysosome that releases enzymes (hyaluronidase) (across) to help the sperm penetrate the corona radiate and zone pellucida
What are the steps in fertilization
- Sperm penetrates the egg, 2. Fusion of plasma membranes of sperm and oocyte, 3. Formation of male pronucleus, 4. Completion of second meiotic division of oocyte and formation of female pronucleus, 5. Fusion of pronuclei to form a zygote (diploid).
How does the egg prevent polyspermy?
When a sperm enters the egg, there is a cortical reaction where the oocyte membrane becomes impenetrable to other sperm. There is also a zoo reaction where the zona pellucid alters its structure to prevent other sperm from binding and penetrating.
What happens during the formation of the male nucleus?
The tail and mitochondria of sperm degrade because sperm are only needed for genetic material.
All the mitochondria in the embryo comes from
The mother
After fertilization the zygote undergoes a series of mitotic cell divisions known as _ as it migrates to the _
cleavage; uterus
About 3 days after fertilization (12-32 cell stage) the embryo is termed a
morula (mulberry)
The morula consists of a solid ball of cells with an
inner and outer cell mass
The inner cell mass will become the _ and the outer cell mass will become the _
embryo; placenta
The morula will enter the uterus by
day 4
Fluid from the uterus penetrates the zone pellucid into the morula and forms a
hollow cavity transforming the morula into a blastocyst
The fluid filled cavity of the blastocyst separates the blastomeres of the inner and outer cell mass into the
Trophoblast (outer cell mass) and the embryo blast (inner cell mass)
The trophoblast is the
thin, outer layer that will make hCG which is the basis for pregnancy testing
The embryo blast is
a group of centrally located blastomeres
about 2 days after entering the uterus the blastocyst will
shed its zone pellucida in what is known as hatching, which allows the blastocyst to increase in size
At the end of week 1, the blastocyst will attach to the
uterine endometrium at its embryonic pole and the trophoblast will invade the uterine wall
What is an abnormal blastocyst
Most won’t produce any sign of pregnancy because trophoblast is defective and can’t produce enough hCG to maintain corpus luteum.
What are Hydatidiform moles
Trophoblast develops and forms placental membranes will little or no embryonic tissue present. These moles contain “grape-like” vesicles and secrete high levels of hCG that may produce benign or malignant tumors. These end as spontaneous abortion or miscarriage.
What is In Vitro fertilization?
Mature oocytes from stimulated ovaries are retrieved transvaginally with sonographic guidance. Sperm and ova are combined in vitro to force fertilization. If this is successful, viable embryos are transferred into the endometrial cavity.
What is intracytoplasmic sperm injection?
Applicable to male factor infertility. The corona radiate is enzymatically digested and a single sperm is injected through the zone pellucid and oocyte cell membrane.
The trophoblast will differentiate into what 2 layers?
Cytotrophoblast (inner layer of mono nucleated cells with mitotic capacity) and synctiotrophoblast (outer multinucleated zone that invades the uterine endometrium to implant the blastocyst; process hCG)
Implantation is completed by
the end of week 2
Site of implantation is marked temporarily by
a fibrin plug
What is an abnormal implantation in the uterus?
Placenta previa- the blastocyst may implant close to the internal os of the cervix. The placenta may cover the internal os that results in painless vaginal bleeding in the late stages of pregnancy.
What is an abnormal implantation outside the uterus?
Ectopic pregnancy give signs and symptoms of pregnancy with abdominal pain and tenderness.
Where do ectopic pregnancies typically occur?
95% occur in the uterine tube but may also implant in the abdominal cavity in either the rectouterine punch or pouch of douglas
The embryo blast will differentiate into which 2 layers?
The dorsal epiblast and the ventral hypoblast (transition structure that doesn’t form anything in the adult)
Within the epiblast, clefts develop to form
the amniotic cavity and the amnion
hypoblasts migrate and line the inner surface of the cytotrophoblast which forms the
exocoelomic membrane (or Heuser’s membrane)
The exocoelomic membrane surrounds a space known as the
primitive or primary yolk sac (primary umbilical vesicle)
What proliferates to fill the space between the cytotrophoblast and either the amnion or primitive yolk sac?
Extraembryonic mesoderm
Cavities form within the extra embryonic mesoderm to form the
chorionic cavity (extraembryonic coelom)
The chorionic cavity is surrounded by the
chorionic membrane
The chorionic membrane is formed by the
extra embryonic mesoderm, cytotrophoblast, and the synctiotrophoblast.
The extra embryonic mesoderm at the embryonic pole does not cavitate but instead forms
the connecting stalk which will become the future umbilical cord.
The hypoblast produces cells that migrate along the inner surface of the primitive yolk sac to form
the definitive or secondary yolk sac/umbilical vesicle
During formation of the definitive yolk sac, large portions of the primitive yolk sac are pinched off as
exocoelomic cysts in the chorionic cavity
