Fertilization and Implantation

Question 1

When in the menstrual cycle does Fertilization occur?

Answer 1

Day 15-16

Question 2

What is the closest layer of Cumulus cells that are surrounding the Oocyte?

Answer 2

Corona Radiata

Question 3

What is the Cumulus cell layer that is going to form a “Stalk” next to the Mural Granulosa Cells?

Answer 3

Cumulus-Oophorus Cells

Question 4

Estrogen is going to be important in the delivery of sperm to the Ampulla of the Ductus Deferens. What functions does it play in this process?

Answer 4

1. Causes Cervix to secrete a Watery Mucus (Forms channels to aid in the passage of sperm through the Cervix)
2. Causes Contractions of the MYOMETRIUM to help propel sperm

Question 5

Describe the process of Capacitation.

Answer 5

• Event that occurs in the oviduct where the spermatozoan is modified so that it is capable of fertilizing the egg
• ACROSOME Reaction
• Uncapacitated Sperm only make it to the Isthmus of the Uterine Tube

Question 6

What are the Three barriers that sperm need to pass before they are able to fertilize the ovum?

Answer 6

1. Corona Radiata
2. Zona Pellucida
3. Plasma Membrane of the egg (oolemma)

Question 7

Describe the process of Fertilization.

Answer 7

1. Sperm head attaches through zona pellucida (Sperm-ZP3 interaction)
2. Acrosomal Reaction
   - Increase [Ca2+] inside the sperm triggers fusion of the outer acrosomal membrane of egg with the sperm cell’s plasma membrane
3. Spermatozoa penetrates the Zona Pellucida
4. Cell membranes of the sperm and Oocyte will fuse
5. Cortical Reaction
   - Increase [Ca2+] inside the Oocyte which will cause exocytosis of enzymes that will act on the Zona Pellucida to HARDEN it (Prevents POLYSPERMY)
6. Increase [Ca2+] in Oocyte cause completion of 2nd meiotic division and results in the formation of the 2nd POLAR BODY
7. Sperm nucleus decondenses and transforms into the male pronucleus
8. Male and female PRONUCLEI FUSE forming the ZYGOTE

Question 8

Which event will mark the end of Fertilization and the beginning of Embryonic Development?

Answer 8

Mingling of the Chromosomes

Question 9

When does implantation of human blastocyst occur?

Answer 9

6-7 Days Following Ovulation

Question 10

Which hormone is responsible for the transformation of Stromal cells to Decidual cells in the endometrium of the Uterus?

Answer 10

Progesterone

Question 11

Which cell is going to enter the Uterine Cavity?

Answer 11

Blastocyst

Question 12

How many days after Ovulation does it take to make the Morula?

Answer 12

3 Days

Question 13

In which cell is the Zona Pellucida degraded?

Answer 13

Late Blastocyst (“Hatched”)

Question 14

Which layer of cells in the blastocyst will form the Embryo Proper?

Answer 14

Inner Cell Mass Layer (Pluripotent)

Question 15

Describe the purpose and regulation of Pinopods.

Answer 15

• Small, finger-like protusions on endometrial cells that are responsible for ENDOCYTOSIS of macromolecules and uterine fluid in the lumen of the Uterus
• Progesterone will ENHANCE
• Estrogen will INHIBIT

Question 16

What is the function of Human Chorionic Gonadotropin hormone?

Answer 16

• Prevents menstruation by sustaining the function of the CORPUS LUTEUM, signaling the mother’s body that she is PREGNANT
• hCG is going to act as LH and promotes the trophoblast growth and placenta development

Question 17

Why is Human Chorionic Gonadotropin hormone important for the first 10 weeks of pregnancy?

Answer 17

hCG is responsible for maintaining the corpus luteum for the first 10 weeks and then the PLACENTA takes over by secreting PROGESTERONE

Question 18

What is the initial event for Implantation?

Answer 18

Blastocyst coming in contact with the Uterine Wall

Question 19

What are the is the main secretory product of the Syncytiotrophoblast?

Answer 19

Human Chorionic Gonadotropin Hormone

Question 20

Describe the process of Hatching.

Answer 20

• Blastocyst gets rid of Zona Pellucida
• Occurs 6-7 days after Ovulation
• Blastocyst factors take part in converting Plasminogen (Found in the Uterine Cavity) into PLASMIN which will DEGRADE the Zona PELLUCIDA

Question 21

Describe the three stages of Implantation.

Answer 21

1. APPOSITION: Earliest contact between the blastocyst wall, traphoectoderm and endometrial epithelium
2. ADHESION: Trophoblast attaches to the Uterine Epithelium though the MICROVILLI of the trophoblast, Ligand-Receptor interactions are probably involved
3. INVASION: Syncytiotrophoblast is going to penetrate the basement membrane of the uterine tube and reach the Uterine Stroma