Embryology: Fertilization Flashcards
Gametogenesis
Production of gametes (oocytes and spermatozoa)
Location of Fertilization
Uterine tubes, first 1/3 (lateral)
Purpose of Corona Radiata in Fertilization
Keep ovum from planting where it shouldn’t, control sperm. Implantation is ideally done in the endometrium in uterus.
Restriction event
Changing a cell from one type to another, definitive, rate limiting step
Zona Pellucida – Cortical Reaction
Zona Pellucida has sperm receptors that recognize integral proteins of sperm PM
Polyspermy
Fertilization by more than one sperm
Acrosome (of sperm)
Head of sperm that contains hydrolytic enzymes used to breakdown zona pellucida
Stages of Fertilization (2)
- Penetrate corona radiata
- Sperm bind to and penetrate zona pellucida
**Acrosome reaction follows to prevent polyspermy
Cortical Reaction (2 stages)
- Fast component: change in resting potential of oocyte (prevent binding of sperm)
- Slow component: release of cortical granules (destroy sperm receptors, ZP3)
ZP3 removal prevents sperm-egg binding and fertilization
Results in infertility
Izumo
Protein required for sperm to fuse with eggs
Monozygotic Twins vs. Dizygotic Twins
- Monozygotic Twins = Identical, same sex. Occurs when fertilized egg splits into two.
- Dizygotic Twins = Fraternal. Two separate eggs are fertilized.
Polar Twins (Half-Identical)
Happens with egg splits before fertilization and polar body is also fertilized by different sperm.
Resultant twins share half genes in common. Assumes polar body has enough material to last through implantation.
Females are always mosaics
Mosaicism – cells within one individual have different genetic makeup, results from mitotic error
Blaschko’s lines
Chimera
Genetically different cells, different zygotes (started as two separate people, ended as one)
Mosaics vs. Chimera
Both contain genetically different cells, mosaic comes from one zygote. Chimera comes from two different zygotes.
Lyonization
Random X-chromosome inactivation
Blastomeres
Beginning mitotic division of gametes, totipotent
Ectopic pregnancy
Is implantation of embryo anywhere other than endometrial lining of uterus
Restriction event in implantation
Transition from morula to blastocyst – two cell types, epiblasts and trophoblasts (pluripotent)
Zona pellucida dissipates at the start of implantation
Only need it until embryo is implanted at correct location
Hatching of Human Embryo
Blastocyst must secrete proteases to digest zona pellucida and implant onto endometrium
Embryonic stem cell source
Inner cell mass (from blastocyst)
Components of blastocyst
- Inner cell mass (embryoblast)
- Outer cell mass (trophoblast)
- Blastocoele (cavity)
Need both embryoblasts and trophoblasts to make a fetus
Embryoblast
Eventually creates embryo, differentiates to hypoblast and epiblast
Trophoblast
Eventually becomes placenta, differentiates to cytotrophoblast and syncitiotrophoblast
Totipotent stem cells
Have potential to grow into an entire organism
Pluripotent stem cells
Cannot grow into an entire organism but can derive any of the three germ layers
Twinning
- Cleavage of early embryo
- Splitting of ICM
- Incomplete division of ICM (conjoined siamese twins)
Parasitic twin (craniopagus parasiticus)
Incomplete twin grows, not functional organism.
Fetus in fetu
Inclusion twinning, fetus gets trapped and grows inside of its twin. Is a living entity because it is attached to host.
