Fertilization and Implantation Flashcards
What is sperm capacitation?
incapacitated sperm bind actively to the epithelial cells of the isthmus and become unbound when they are capacitated
When sperm bind to the isthmus, they become capacitated. What is this binding process?
slows capacitation
extends sperm lifespan
increases probability of sperm being in the oviduct when egg shows up
Capacitation is associated with hyperactivity. Why is this a benefit?
helps sperm to get chemical signals from oocyte
involves a change in flagella motion which helps it fetach from epithelium and increase mobility to get to egg
What is fertilization?
When the sperm binds the corona radiata and gets through that and the zona pellucida and the plama membrane of the oocyte
How does the sperm get throught the corona radiata (cumulus)
How does the sperm get through the zone pellucida?
made of hyaluronic acid, the sperm digest it with hyaluronidase
made of glucoproteins, sperm contain receptors for those (ZP3) and binds to trigger the acrosome reaction
What is the acrosome reaction?
- Sperm ZP3 receptor binds to ZP3 on the ZP
- inner sperm plasma membrane fuses with outer acrosomal membrane to release contents of acrosomal vesicle
- enzymes in vesicle digest ZP
- sperm can then enter the lil hole they made to get to the plasma membrane
What happens when the sperm get to the plasma membrane?
possess a protein called Izumo which binds to Izumo receptor on oocyte
entire sperm enters the egg and DNA decondenses and forms a pronucleus around the DNA
The sperm and egg fusing triggers what?
What is that?
The cortical reaction
release of Ca that alters ZP proteins to block entrance of additional sperm and hyaluronic acid, proteinases and others are released to make a physical barrier to other sperm entery
PREVENTS POLYSPERMY
How is the zygote formed?
- Ca release after sperm entry triggers Meiosis II and release of polar body
- pronucleus forms around female DNA and the chromosomes replicate as pronuclei move togehter and fuse
- the fusion of the pronuclei initiates first embryonic cleavage (the beginning of embryonic development
Detail the first week of embryonic development
cleavage day 1
morula day 3
early blastocyst day 4
implantation day 6-8
What is embryonic cleavage?
cell undergoes mitotic divisions and cells become smaller
blastomeres are totipotent and embryo reaches 16 cell morula by day 3
What is compaction and blastocele development?
outer cells of morula increase cell-cell adhesion via desmosomes and tight junctions to form trophoectoderm
inner cells become the inner cell mass which will form the embryo (pluripotent)
What is blastocyst hatching?
hatching of embryo from zona pellucida prior to implantation
trophoblasts secrete proteases thhat digest ZP
- inability to hatch can cause infertility*
- premature hatching can cause abnormal implantation*
How does the blastocyst prevent rejection from The Host Mother?
blastocyst secretes molecules that maintain pregnancy, promote implantation and placental development including immunosuppressive and immune regulating factors
What is the role of HCG in early pregnancy?
secreted by trophoblasts and synctiotrophoblasts
prevents involution of CL
prevents menstruation and incerases progesterone/estrogen sexretion
functions as an autocrine growth factor to help trophoblast and placental growth
Describe the apposition stage of implantation
contact between endometrium and trophoblasts
typically ina crypt in the endometrium
inner ell mass rotates near the endometrial epithelium
Describe the attachment stage of implantation
trophoblasts ashere to endometrium and interact with surface proteins between the two
this initiates changes in the endometrial stroma causing decidualization:
- increases vascular permeability
- intracellular matrix composition
- stromal cell morphology
Describe the invasion stage of implantation
degradation of endometrial epithelial cells
trophoblast fusion and formation of synctiotrophoblasts which then protrude through basement membrane and reach endometrial stroma
What are the main functions of synctiotrophoblasts?
express adhesive surface proteins
breakdown extracellular matrix
secrete HCG
funciton in phagocytosis and bidirectinoal placental transfer of gasses
Decidualization is the response of maternal stromal cells to what?
invasion and progesterone
once the decidua has formed it is ready for implantation by the embryo and forms adhesive junctions that migrate to implanting embryo to help it along
production of signals prevent the embryo from invading into the myometrium which would cause catastrophic hemorrhage during delivery
What is ectopic implantation?
implantatino other than in uterine fundus
most common is oviduct
no decidualization occurs thus invasion is not controlled and can cause rupture of tissues and hemorrhage
During placentation, spaces withi the synctiotrophoblast appear called ?
What do they do?
lacunae
break maternal capillaries and get filled with secretions, blood, and matrix for nutrient transfer
During placentation, the proliferation of synctiotrophoblsats and cytotrophoblasts to lacunae become what?
mesenchume cells from extraembryonic mesoderm invade villie and become what?
eventually mesenchymal cells form fetal blood vessels de novo making what?
1’ villi
2’ villi
3’ villi
