Fertilization and Implantation Flashcards
Where does fertilization take place?
Ampulla
What is sperm capacitation?
- Sperm are coated with proteins & glycoproteins in the epidydimis& after ejaculation they become coated with seminal plasma proteins
- Capacitation occurs once exposed to female tract, the coatings are removed exposing molecules that will allow the sperm to bind with the zona pellucida on the oocyte
- occurs inside the isthmus
What is a theory for capacitation iniation and significance of sperm binding?
- Signals come from process of ovulation itself leading to capacitation of sperm ocne they reach the oviduct. Sperm binds epithelial lining slowing capacitation process and extetds sperm life within oviduct until ovum is present
What is the significance of a hyperactive sperm?
- It is assoc. with wsperm capacitation and chemical signals from the oocyte
- It is necessary for sperm to detach from oviduct epithelium
- Increases their mobility and helps them propel through the outer layers of egg to reach plasma mem
How does the sperm get through the cumulus cell matrix?
Digests the matrix with membrane bound hylauronidase
What three barriers do sperm have to make it past for fertilization to occur?
- Corona radiata
- ZP
- Plasma mem of oocyte
How does the sperm make it through the ZP?
- Sperm has ZP3 receptors after it undergoes capacitation
- Binding ZP3 triggers the acrosome reaction
What is the acrosome reaction?
- Inner sperm plasma mem fuses with the outer acrosomal membrane and releases contents of the acrosomal vesicle
- Enzymes in the vesicle digest the ZP and sperm can enter
How does the sperm make it past the plasma membrane?
- After the acrosome reaction, the sperm reaches the plasma membrane and uses a protein called Izumo which binds to receptor on the oocyte
- Entire sperm enters the egg during fusion and the DNA de condenses and a Pronucleus forms around that DNA
What is the cortical reaction?
- Fusion of sperm and egg triggers it
- Altering the ZP proteins occurs which prevents other sperm from binding
- ZP forms a physical barrier preventing polyspermy
What does the calcium release in the cortical reaction trigger?
- Stimulates completion of meiosis II
- breakdown of MAPK proteins and a second polar body is released
How does egg activation occur?
- Egg activation occurs as sperm DNA condenses and pro nucleus forms around the female chromosomes
What initiates the first embryonic cleavage?
- The male and female chromosomes replicate as pronuclei move together and fusion of the pronuclei will initiate the first embryonic cleavage
What occurs during week one of embryo development?
- Cleavage!
- Morula ~16 cell on day 3
- Early blastocyst day 4
- Implantation day 6-8
Once the cell reaches the morula stage what occurs?
Compaction and blastocele development
- Outer cells of the morula increase cell-cell adhesion via desmosomes and TJxns
- Inner cells become the ICM which will form the embryo proper
- Pluripotent cells
What is blastocyst hatching?
Trophoblast secretes proteases that will diges the zona pellucida allowing the embryo to “hatch”
What cell synthesizes and secretes molecules that promote pregnancy and promote implantation and placenta dev?
Blastocyst
What secretes hCG?
trophoblasts and syncytiotrophoblasts after implantation
What does hCG do, what is its structure similar to?
- Prevents involution of corpus luteum, prevents menstruation
- Leads to increase of progesterone and estrogen
- Autocrine growth factor
- stimulates trohpblast growth and dev
- Stimulates placenta dev
- Similar structure to LH
What are the stages to implantation?
- Apposition: contact btw endometrium and trophoblasts ICM rotation near endometrial epi
- Attachment: trophoblast cells (TBC’s) adhere to luminal endometrial epithelium interactionn btw surface proteins on TBC’s and epithelial cells
- Initates changes in endometrial stroma- decidualization
- Invasion: degredation of endometrial epi cells, TBC fusion and formation of syncytiotrophoblasts, STB protrudes thorugh basesment mem and reaches endometrial stroma
What is decidualization?
- Response of the maternal stromal cells to invasion and progesterone, the endometrial stroma is transformed into enlarged and glycogen filled dicidual cells
- decidua forms epi sheet with adhesive junctions that prevents migration of the embryo
- Also produces signals that will prevent the embryo from invading the myometrium preventing postpartum hemorrhaging
What functions do the syncytiotrophoblasts have?
- Adhesive surface proteins
- Breaks down ECM
- hCG secretion
- Become highly steroidogenic at 10 weeks and can maintain pregnancy independent of the CL
- Has fxns in phagocytosis and bidirectional placental transfer of gases and nutrients and wastes
What is the most common site for ectopic pregnancy?
oviduct, more specificallly ampulla
What is placentation?
- Lacunae that appear within the syncytiotrophoblasts around day 9
- Breaks down maternal capillaries
- filled with endometrial secretions, maternal blood, digested matrix for nutrient transfer
What does premature hatchiung of the blastocyst result in?
Abnormal implantation
