Fertilization and Implantation Flashcards
Both the sperm and the oocyte must travel to where for fertilization?
Ampulla of oviduct
What must happen in order to expose binding sites of the sperm for the ooctye’s zona pellucida?
Sperm Capacitation
Epididymal sperm’s plasma membrane is coated with what?
Many surface molcules/proteins
The sperm that is then ejaculated becomes coated with?
Seminal plasma
Describe seminal plasma
Seminal plasma proteins coat the surface molecules on the sperm that is ejaculated
Once the ejaculated sperm reaches the female tract, then what occurs?
Capacitation
Describe capacitation
The seminal plasma coatings and sperm surface molecules are REMOVED to expose portions of the sperm that can bind with the oocyte’s zona pellucida
Incapacitated sperm (have yet to undergo capacitation) can bind to?
Epithelial cells in the oviductal isthmus
What does the binding of incapacitated sperm to the isthmus do?
Extends the sperm lifespan
INCREASES the probability that the sperm will be in the oviduct when the egg is ovulated!
Once incapacitated sperm are capacitated what happens?
They are unbound from the isthmus
What creates a hyperactive sperm?
Sperm capacitation + Chemical signals from oocyte
Hyperactivation of sperm results in what physical change?
A change in flagella motion from wave-like to whip-like
What 3 things does hyperactivation of sperm help with?
- Increases sperm mobility
- Detaches sperm from the epithelium
- Helps propel the sperm through the outer layers of the egg to reach the plasma membrane
What 3 barriers must be breached during fertilization?
- Expanded cumulus (corona radiata)
- Zona pellucida
- Oocyte plasma membrane
What is the cumulus cell matrix of the oocyte made of?
Hyaluronic acid
What does the sperm use to digest the cumulus cell matrix of hyaluronic acid?
Hyaluronidase
The zona pellucida of the oocyte contains glycoproteins. Which one does the sperm have a receptor for?
ZP3
Once the sperm binds ZP3 on the oocyte, what happens next?
Acrosome reaction
Describe the acrosome reaction
- The sperm’s plasma membrane fuses with its acrosomal membrane
- This causes release of acrosomal enzymes
- These enzymes digest the zona pellucida locally
- The sperm can then push forward toward the plasma membrane of the oocyte
What protein does the sperm possess to bind to the oocyte plasma membrane?
Izumo protein of the sperm binds to the Izumo receptor on the oocyte plasma membrane
Once the sperm Izumo protein binds to its receptor on the oocyte, then what happens?
The sperm enters the egg
Once the sperm enters the egg, list the main things that occur next
- Sperm DNA de-condenses
- Pronucleus membrane forms around DNA
- Cortical reaction
- Male and female chromosomes replicate as pronuclei move together
- Fusion of pronuclei = beginning of embryonic development!
Describe the cortical reaction
Triggered by the fusion of the egg and the sperm
- Release of Ca++ alters zona pellucida proteins that BLOCKS the binding of other sperm to prevent polyspermy
What does the cortical reaction prevent?
Polyspermy (binding of additional sperm to the oocyte)
Cleavage
Cell division without growth
Main steps in week 1 embryonic development
Cleavage
Embryo reaches 16 cell stage morula
Early blastocyst
Implantation
Around what day is implantation
Day 8
What is blastocyst hatching?
Hatching of the embryo from the zona pellucida prior to implantation
Inability for the blastocyst to hatch can result in?
Infertility
Premature blastocyst hatching can result in?
Abnormal implantation
hCG
Human Chorionic Gonadotropin
What secretes hCG?
Trophoblasts and Syncytiotrophoblasts
What are the functions of hCG?
Prevents menstruation
Increases progesterone and estrogen secretion
Stimulates trophoblast and placental growth
What are the main stages of implantation?
- Apposition
- Attachment
- Invasion
Describe the apposition phase of implantation
Contact between the endometrium and trophoblasts
- Usually in a crypt of endometrium
- Inner cell mass rotation near endometrial epithelium
Describe the attachment phase of implantation
Trophoblast cells adhere to endometrial epithelium
- Initiates decidualization
Describe the invasion phase of implantation
Degradation of endometrial epithelial cells AND
Trophoblast fusion and formation of syncytiotrophoblasts
What can the syncytiotrophoblasts do during implantation?
Protrude through basement membrane and reach endometrial stromal cells
Main attributes of syncytiotrophoblasts?
- Express surface adhesive proteins
- Breakdown of endometrial extracellular matrix
- Secrete hCG
- Phagocytosis and bidirectional transfer of materials
What are the things syncytiotrophoblasts can secrete to help break down the endometrial extracellular matrix?
Metalloproteinases and Angiogenic factors
Decidualization occurs in what phase of implantation?
Attachment
Decidualization
Maternal stromal cell changes in response to invasion and progesterone
During decidualization, what do the stromal cells change to?
Enlarged, glycogen-filled cells
After decidualization, the endometrium is called?
Decidua
After decidualization, the endometrium is ready for?
Implantation
What 2 things does the decidua do?
- Forms sheet with adhesive junctions to inhibit migration of embryo
- Production of signals to prevent embryo from invading myometrium
If the decidua does not not allow the embryo to invade the myometrium, what can occur?
Postpartum hemorrhage
Ectopic implantation
Implantation anywhere other than the fundus of the uterus
With an ectopic implantation, what does not occur?
Decidualization
Since decidualization does not occur with an ectopic pregnancy, the invasion is NOT controlled. What will this cause?
Rupture of tissues = hemorrhage
Placentation
Spaces appear within syncytiotrophoblasts around day 9
- Formation of primary, secondary and tertiary villi
Primary villus
Syncytiotrophoblasts and cytotrophoblasts
Secondary villus
Primary villus + mesenchyme
Tertiary villus
Secondary villus + fetal blood vessels formed de novo
