embryology-first two weeks Flashcards

Human chorionic gonadotropin
Terms Definitions
epiblast becomes?
In fertilization, when uterine endometrial cells die a preprogrammed death as the syncytiotrophoblast cells of the conceptus approach to replace them
The primary endoderm of the embryoblast, this cell layer appears about day 7 on the embryoblast facing the blastocele. Will form the ventral side of the embryo.
A period of conditioning after ejaculation in the uterus or uterine tubes, lasting about 7 hours, in which the sperms acrosome is altered. Sperm cannot fertilize until this has occured
does the trophoblast make a contribution to the embryo
What is hCG?
Human Chorionic Gonadotropin: essential hormone for pregnancy: maintains proliferation of corpus luteum, secretes hormones - keeps uterine lining:receptive state
In the uterus, the thin, external layer of cells that is where the blastocyst attaches
Extraembryonic mesoderm
Cells that form between the cytotrophoblast and the exoceolomic membrane, separating the two
A layer of cells that differentiates from the embryoblast, it forms the embryonic-pole facing lining of the amniotic cavity
A division of the trophoblast that begins seeping into the endometrial epithelium, where the cell walls combine to form a large polynucleated protoplasmic mass. By day 7 (1 day after implantation) it has encompassed maternal arterial and veinous capillaries and is supplying blood to the developing blastomeres. By the time the extra-embryonic coelomic space is forming it has totally surrounded the cytotrophoblast and the entire conceptus is on the other side of the endometrial lining of the uterus.
Thin outer wall of blastocyst - becomes placenta
tightly packed ball of cells called what?
Primary umbilical vesicle
Drops off the original umbilical vesicle and remains connected by a small amount of mesoderm (the secondary umbilical vesicle remains where the original was, but is somewhat smaller)
Extraembryonic somatic mesoderm
The extraembryonic coelom splits the extraembryonic mesoderm into two layers - this one surrounds the trophoblast (as before)
Embryonic Pole
The normal point of implantation, also the area of the embryoblast
blastula cells are what?
blastomeres – these are totipotential: each capable of producing complete organism
what does this mean?
blastomeres maximize contact with each other, creating a tightly-packed ball of cells
Exocoelomic Membrane
Grows out from the sides of the hypoblast and grows around the inside of the cytotrophoblast, and soon separates from it, leaving an interstitial space known as the extraembryonic mesoderm. When the separation is complete (by day 12) this membrane becomes known as the endoderm!
Six Phases of Fertilization
Passage of Sperm through Corona Radiata
Penetration of Zona Pellucida
Fusion of Plasma Membranes of oocyte and sperm
Completion of 2nd meiotic division & formation of female pronucleus (from decondensation of 1n chromosomes)
Formation of male pronucleus (by dissolution of sperm tail inside now-mature oocyte)
As pronuclei fuse into singe 2n aggregation, ootid becomes zygote
what % of ectopic pregnancies are tubal?
more than 90%
what occurs within the cytotrophoblast as the syncytiotrophoblast is forming?
cytotrophoblast cells are flattening within the blastocyst cavity, a layer next to the cavity is formed, called the hypoblast.
correct or normal implantation site?
upper wall of the uterus.
Acrosome Reaction
When the acrosome of a sperm binds to the zona pellucida of the oocyte, binding occurs that releases enzymes that cause complex changes which makes fertilization possible
what does the hypoblast become?
hypoblast cells multiply and spread, grow together to create a sac called the primitive yolk sac (within the cytotrophoblast
main events of first two weeks
transport to implant site, development of bilaminar embryo, amniotic cavity & embryonic disc, implantation
what occurs during subsequent cleavages of the morula?
blastomeres become arranged either on the inside or the outside of the morula – this is the first sign of differentiation.
hormone that is basis for pregnancy test?
HCG - Human Chorionic Gonadotropin
Does hypoblast contribute to fetus?
No. Is replaced by endoderm during gastrulation
contact method: trophoblast with endometrium?
has tissues that bind with the surface of the uterus.
occurs with trophoblast about 5 days after fertilization?
trophoblast produces enzymes - disrupt zona pellucida
Dispermy (or generally, Polyspermy)
When a egg is fertilized by more than one sperm
two possible treatments for tubal pregnancies?
salpingotomy: making hole in tube – extracting embryo from tube (problem as some embryo may be left behind, necessitating re-operation) may also create scarring rendering tube useless.salpingectomy – removal of tube.
If a woman presents with vaginal bleeding, what should she be treated as?
pregnant until proven not pregnant (with tubal pregnancy and hemmorhage).
embryo movement down uterine tube why?
smooth muscle in the muscularis of the uterine tube, and beat of cilia on epithelial lining of tube.
why do spontaneous abortions go unrecognized by mothers?
because they are during the first two weeks (woman simply thinks her period is late)
what occurs at the eight cell stage?
compaction (between the 3rd & 4th cleavage divisions)
what occurs during the 2nd week following fertilization?
embryo implants in the lining of the uterus and the amniotic cavity and primitive yolk sac are formed.
when does the first cleavage division occur?
abt. 24 hrs after production of 2nd polar body
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