Fertilization and Implantation

Question 1

Incapacitated sperm end up actively binding to the epithelial cells in the isthmus of the oviduct, and can only become unbound when they are capacitated. What are 3 positive results of the incapacitated sperm binding?

Answer 1

1. slows capacitation process
2. extends sperm lifespan
3. increases probability that sperm will be there when egg is ovulated

Question 2

Capacitation involves a change in flagella motion from wave like to whip like, failure of this transformation would result in which of the following?

A. Sperm detaching from oviduct epithelium

B. Increase in mobility

C. Reduced ability of sperm to move through outer layers of the egg

D. None of the above

Answer 2

A. Sperm detaching from oviduct epithelium-sperm would struggle to detach

B. Increase in mobility- decrease mobility

C. Reduced ability of sperm to move through outer layers of the egg

D. None of the above

Question 3

What 3 barriers must sperm get through once bound to the egg?

Answer 3

1. corona radiata (cumulus)
2. zona pellucida
3. oocyte’s plasma membrane

Question 4

Express how sperm get through each of the three barriers

1. Corona radiata:
2. Zona pellucida:
3. Plasma Membrane:

Answer 4

1. Corona radiata: sperm’s hyaluronidase breaks down the hyaluronic acid in the corona radiata
2. Zona pellucida: sperm’s ZP3 receptor binds ZP3 in ZP and triggers acrosome reaction –> acrosomal vesicle contents digest ZP
3. Plasma Membrane: sperm uses Izumo protein and binds to egg’s izumo receptor allowing sperm to enter egg

Question 5

What reaction is responsible for altering the ZP proteins in the egg in such a way that the adding of additional sperm is blocked?

A. Binding of sperm’s ZP3 receptors to ZP3 on egg

B. Hyaluronidase breaks down hyaluronic acid

C. Fusion of sperm and egg triggering the release of Ca 2+

D. None of the above

Answer 5

A. Binding of sperm’s ZP3 receptors to ZP3 on egg -triggering of acrosome reaction

B. Hyaluronidase breaks down hyaluronic acid - how it gets through corona radiata

C. Fusion of sperm and egg triggering the release of Ca 2+- cortical reaction

D. None of the above

Question 6

Why does release of Ca2+ stimulates completion of meiosis II and release of second polar body?

A. breaks down MAPK proteins

B. breaks down cAMP proteins

C. brekas down cGMP proteins

D. All of the above

Answer 6

breaks down MAPK proteins

Question 7

Which of the following events initiates the first embryonic cleavage, thus signifying the beginning of embryonic development?

A. Formation of pronucleus around the sperm and egg respectively

B. sperm DNA decondensing, then the formation of the pronucleus around the female chromosome

C. replication of the female chromosomes as the pronuclei move together

D. Fusion of the pronuclei surrounding the DNA in the sperm and egg

Answer 7

Fusion of the pronuclei surrounding the DNA in the sperm and egg

Question 8

In week 1 of embryonic development we see cleavage, which is cell division without growth. On what day do we see the embryo reach 16 cell stage (morula)?

What day(s) does implantation occur?

Answer 8

Morula: Day 3

Implanatation: Day 6-8

Question 9

T/F: The timing for release of proteases from the Trophoblast to destroy ZP and allow embryo to hatch has a very important time component, as early hatching can lead to normal implantation, and failure to hatch can result in infertility

Answer 9

True

Question 10

In which stage of implantation is decidualization initiated so that the endometrium stromal cells change to allow for interaction between maternal and fetal side of placenta?

A. Apposition

B. Attachment

C. Invasion

Answer 10

A. Apposition- ICM rotates near the endometrial epithelium in the posterior wall of the uterine fundus

B. Attachment- trophoblast adheres to endometrial stroma and initiates changes in it’s structure

C. Invasion-

Question 11

At what week might we see synctiotrophoblast become highly steroidogenic and able to make progesterone independntly of CL?

A. Week 5

B. Week 6

C. Week 8

D. Week 10

Answer 11

Week 10

NOTE: synctiotrophoblast expresses adhesive surface proteins, breaks down extracell matrix, and secretes hCG

Question 12

The embryo implanting erroneously into the myometrium during implanatation would likely result in what issue at birth?

Answer 12

Hemorrhage (post partum hemorrhage)

Question 13

Ectopic pregnancy is implantation somewhere other than the fundus. The most common site of ectopic pregnancy is within the oviduct, but what region within the oviduct (uterine tube) is the most common?

A. Infundibulum (Fimbrae)

B. Ampulla

C. Isthmus

D. All are even

Answer 13

Ampulla

Ampulla > Isthmus > Fimbrae