Lecture 6: Implantation

Question 1

Fertilization

Answer 1

Ampulla within 12 hours of ovulation

Question 2

blastocyst hatching

Answer 2

• The zona pellucida surrounds the developing embryo until it reaches the uterus.
• The shedding of the zona pellucida is accomplished through a process called blastocyst hatching.

Question 3

Major functions of the zona pellucida(READING FROM BOOK)

Answer 3

Promotes maturation of oocyte and follicle

The ZP serves as a barrier, only allows the sperm of the same species to access the egg.

Initiates the acrosomal reaction

Prevents polyspermy

Porous filter during cleavage, only substances secreted by the uterine tube can reach the embryo

Immunological carrier between mother and antigenic ally different embryo

Prevents blastomeres of cleaving embryo from dissociating.

Facilitates the differentiation of trophoblastic cells

Prevents premature implantation of the cleaving embryo into the wall of the uterine tube.

Question 4

Stages of implantation

Answer 4

1. Attachment of expanded blastocyst to the endometrial epithelium.
2. Penetration of the uterine epithelium.
3. Invasion into the tissues underlying the epithelium.
4. Erosion of the maternal vascular supply.

Question 5

Attachment of the expanded blastocyst:

Answer 5

• Initial contact is between the endometrial surface and the embryonic pole of the blastocyst.
• Adhesion molecules(i.e.,integrins)expressed by the endometrium and additional adhesion molecules expressed by the trophoblast cells facilitate attachment.
• Leukemia-inhibiting factor expressed by the endometrium and respective receptors on the trophoblast may be important.

Question 6

Penetration of the Uterine Epithelium and Invasion into Underlying Epithelium

Answer 6

• Trophoblast separates into a cellular cytotrophoblast (closest to inner cell mass) and a multinucleated syncytiotrophoblast (closest to the endometrium).
• Syncytiotrophoblast projections penetrate the endometrial basal lamina and then begin to invade the endometrial stroma.
• Trophoblastic lacunae (hollow cavities within the syncytiotrophoblast) appear.
• Eroded endometrial blood vessels fill trophoblastic lacunae with maternal blood.
• Trophoblast is less invasive at this point.

Question 7

decidual reaction

Answer 7

is the response of the endometrial stroma cells to the invading blastocyst.

Question 8

Without the decidual reaction

Answer 8

the trophoblast potentially might erode all the way through the endometrial wall?

Question 9

Decidual cells that participate in the decidual reaction are derived from

Answer 9

endometrial stroma cells that accumulate glycogen and lipid droplets.

Question 10

The result of the decidual reaction

Answer 10

is a massive cellular matrix that completely surrounds the embryo and fills most of the
endometrium.

Question 11

A primary function of the decidual reaction is to

Answer 11

is to provide an immunologically privileged site to protect the developing
embryo from being rejected.

Question 12

Explain ectopic pregnancies and where they most commonly occur.

Answer 12

Pg 54: Tubal pregnancies: Fimbral 17%, Ampullary 54%, Ovarian .5% (ouch), Isthmic 25%, Intertitial 2%, Cervical 0.3%

There are also conditions such as placenta previa that can cause problems with the pregnancy. See page 54.

Question 13

Clinical correlate question is typed under the “Chapter Questions” card stack

Answer 13

Enjoy!