Fertilization and Implantation

Question 1

What is sperm capacitation?

Answer 1

incapacitated sperm bind actively to the epithelial cells of the isthmus and become unbound when they are capacitated

Question 2

When sperm bind to the isthmus, they become capacitated. What is this binding process?

Answer 2

slows capacitation

extends sperm lifespan

increases probability of sperm being in the oviduct when egg shows up

Question 3

Capacitation is associated with hyperactivity. Why is this a benefit?

Answer 3

helps sperm to get chemical signals from oocyte

involves a change in flagella motion which helps it fetach from epithelium and increase mobility to get to egg

Question 4

What is fertilization?

Answer 4

When the sperm binds the corona radiata and gets through that and the zona pellucida and the plama membrane of the oocyte

Question 5

How does the sperm get throught the corona radiata (cumulus)

How does the sperm get through the zone pellucida?

Answer 5

made of hyaluronic acid, the sperm digest it with hyaluronidase

made of glucoproteins, sperm contain receptors for those (ZP3) and binds to trigger the acrosome reaction

Question 6

What is the acrosome reaction?

Answer 6

• Sperm ZP3 receptor binds to ZP3 on the ZP
• inner sperm plasma membrane fuses with outer acrosomal membrane to release contents of acrosomal vesicle
• enzymes in vesicle digest ZP
• sperm can then enter the lil hole they made to get to the plasma membrane

Question 7

What happens when the sperm get to the plasma membrane?

Answer 7

possess a protein called Izumo which binds to Izumo receptor on oocyte

entire sperm enters the egg and DNA decondenses and forms a pronucleus around the DNA

Question 8

The sperm and egg fusing triggers what?

What is that?

Answer 8

The cortical reaction

release of Ca that alters ZP proteins to block entrance of additional sperm and hyaluronic acid, proteinases and others are released to make a physical barrier to other sperm entery

PREVENTS POLYSPERMY

Question 9

How is the zygote formed?

Answer 9

• Ca release after sperm entry triggers Meiosis II and release of polar body
• pronucleus forms around female DNA and the chromosomes replicate as pronuclei move togehter and fuse
• the fusion of the pronuclei initiates first embryonic cleavage (the beginning of embryonic development

Question 10

Detail the first week of embryonic development

Answer 10

cleavage day 1

morula day 3

early blastocyst day 4

implantation day 6-8

Question 11

What is embryonic cleavage?

Answer 11

cell undergoes mitotic divisions and cells become smaller

blastomeres are totipotent and embryo reaches 16 cell morula by day 3

Question 12

What is compaction and blastocele development?

Answer 12

outer cells of morula increase cell-cell adhesion via desmosomes and tight junctions to form trophoectoderm

inner cells become the inner cell mass which will form the embryo (pluripotent)

Question 13

What is blastocyst hatching?

Answer 13

hatching of embryo from zona pellucida prior to implantation

trophoblasts secrete proteases thhat digest ZP

• inability to hatch can cause infertility*
• premature hatching can cause abnormal implantation*

Question 14

How does the blastocyst prevent rejection from The Host Mother?

Answer 14

blastocyst secretes molecules that maintain pregnancy, promote implantation and placental development including immunosuppressive and immune regulating factors

Question 15

What is the role of HCG in early pregnancy?

Answer 15

secreted by trophoblasts and synctiotrophoblasts

prevents involution of CL

prevents menstruation and incerases progesterone/estrogen sexretion

functions as an autocrine growth factor to help trophoblast and placental growth

Question 16

Describe the apposition stage of implantation

Answer 16

contact between endometrium and trophoblasts

typically ina crypt in the endometrium

inner ell mass rotates near the endometrial epithelium

Question 17

Describe the attachment stage of implantation

Answer 17

trophoblasts ashere to endometrium and interact with surface proteins between the two

this initiates changes in the endometrial stroma causing decidualization:

• increases vascular permeability
• intracellular matrix composition
• stromal cell morphology

Question 18

Describe the invasion stage of implantation

Answer 18

degradation of endometrial epithelial cells

trophoblast fusion and formation of synctiotrophoblasts which then protrude through basement membrane and reach endometrial stroma

Question 19

What are the main functions of synctiotrophoblasts?

Answer 19

express adhesive surface proteins

breakdown extracellular matrix

secrete HCG

funciton in phagocytosis and bidirectinoal placental transfer of gasses

Question 20

Decidualization is the response of maternal stromal cells to what?

Answer 20

invasion and progesterone

once the decidua has formed it is ready for implantation by the embryo and forms adhesive junctions that migrate to implanting embryo to help it along

production of signals prevent the embryo from invading into the myometrium which would cause catastrophic hemorrhage during delivery

Question 21

What is ectopic implantation?

Answer 21

implantatino other than in uterine fundus

most common is oviduct

no decidualization occurs thus invasion is not controlled and can cause rupture of tissues and hemorrhage

Question 22

During placentation, spaces withi the synctiotrophoblast appear called ?

What do they do?

Answer 22

lacunae

break maternal capillaries and get filled with secretions, blood, and matrix for nutrient transfer

Question 23

During placentation, the proliferation of synctiotrophoblsats and cytotrophoblasts to lacunae become what?

mesenchume cells from extraembryonic mesoderm invade villie and become what?

eventually mesenchymal cells form fetal blood vessels de novo making what?

Answer 23

1’ villi

2’ villi

3’ villi