Fertilization, Cleavages And Implantation

Question 1

List of the four major fertilization events

Answer 1

Contact and recognition between sperm and egg
Regulation of sperm entry into the egg
Fusion of the genetic material
Activation of egg metabolism

Question 2

What are cumulus cells?

Answer 2

Cells that surround the oocyte in the follicle and after ovulation

Question 3

What are the roles of the cumulus cells?

Answer 3

Protection, development, fertilization

Question 4

What are corona radiata cells?

Answer 4

Part of the cumulus, innermost layer surrounding the oocyte

Question 5

What is the Zona pellucida?

Answer 5

A matrix that surrounds the oocyte

Question 6

What is the role of the Zona pellucida?

Answer 6

Binds spermatozoa, species specific barrier

Question 7

List the changes in cumulus-oocyte complex of rabbits during follicular maturation and ovulation

Answer 7

In pre-ovulatory follicle, cumulus cells are tightly packed around the oocyte
Pre-ovulation, luteinizing hormone, stimulates the follicle
Cumulus cells produce extracellular, matrix, becoming more spread out by ovulation

Question 8

Is the ovulated oocyte still surrounded by cumulus cells?

Answer 8

Yes

Question 9

How many sperm are ejaculated into the vagina in humans?

Answer 9

About 200 to 300,000,000

Question 10

About how many sperm enter the oviduct

Answer 10

About 400

Question 11

How many sperm choose the wrong oviduct

Answer 11

200

Question 12

What is sperm motility crucial for?

Answer 12

Getting the sperm from the vagina through the cervical mucus and into the uterus

Question 13

How is sperm transported into the ducts?

Answer 13

Uterine contractions

Question 14

What are sperm associations?

Answer 14

In species with promiscuous females, sperm from the same male form aggregate, enabling them to swim faster due to increased flagella or propulsion.

Question 15

What is sperm capacitation?

Answer 15

A final set of biochemical events that change the sperm to enable fertilization of the egg

Question 16

List the three signals secreted by the oviduct for sperm capacitation

Answer 16

Cholesterol is removed, possibly in increasing sperm membrane fluidity
Glycol proteins are lost, which may expose Zona binding proteins
Fluctuations in intracellular calcium levels, which is essential for sperm hyper activation

Question 17

List five effects of capacitation

Answer 17

Hyper activation
Increased rate of metabolism to meet the needs of active sperm
Changes in sperm glycoproteins to prepare for sperm egg binding
The enzyme pro-across in ((inactive)) is converted to acrosin [active)
Increased thermal and chemical sensitivity, which helps the sperm find the egg at the end of the oviduct

Question 19

How does thermal sensitivity help sperm find the egg?

Answer 19

There is a thermal gradient of 2°C along the oviduct, with the egg at the warmest end
The sperm can sense these differences and tend to to move toward the highest temperature

Question 20

How does chemical sensitivity help the sperm find the egg?

Answer 20

Cumulus cells, secrete, progesterone, which attracts sperm

Question 21

What five things happen after sperm enters the egg

Answer 21

The egg is activated by calcium influx
The egg is released from metaphase two
The male pro nucleus is de condensed
The Zona hardens to prevent polyspermy
Zinc, spark

Question 22

What is zinc, spark

Answer 22

Billions of zinc ions are released upon sperm entry into the egg
This prevents polyspermy by inhibiting acrosin enzyme activity

Question 23

What does sperm contribute?

Answer 23

The pro nucleus
The centrosome which is required for cleavage
And the tail which is incorporated into the plasma membrane

Question 24

Describe metabolic egg activation

Answer 24

Waves of calcium pass through the cytoplasm from the side of fusion stimulating completion of the second meiotic division
Calcium ions will cause cortical granules to fuse with the plasma membrane
And later calcium ions will initiate recruitment of maternal RNAs

Question 25

Outline the seven steps of in vitro fertilization

Answer 25

Hormonal stimulation of egg maturation Removal of eggs by laparoscopy Collection of sperm sample, and concentration of the most active sperm In vitro fertilization Early cleavage in vitro Extra embryos frozen Re-implantation of up to three of the embryos

Question 26

How has in vitro fertilization evolved?

Answer 26

Such that sperm is injected directly into the egg

Question 27

When does the first cleavage occur?

Answer 27

About 24 hours after fertilization

Question 28

How much time does it take between each cell division?

Answer 28

About 12 to 24 hours

Question 29

At what day is the two cell stage?

Answer 29

Day one

Question 30

How many days does it take to get to the four cell. stage

Answer 30

Two days

Question 31

How many days does it take to get to the nine cell stage?

Answer 31

2.5 days

Question 32

How many days does it take to get to the 16 cell stage?

Answer 32

Three days

Question 33

What is the name of the 16 cell stage?

Answer 33

The morula

Question 34

How many days does it take to get to the 58 cell stage

Answer 34

Four days

Question 35

How many days does it take to get to the 107 cell stage

Answer 35

Five days

Question 36

What is the 58 cell stage called? Same for the 107 S. stage.

Answer 36

Blastocyst

Question 37

When does compaction occur?

Answer 37

At the eight cell stage

Question 38

What is compaction?

Answer 38

When cells are still separated, but adhere more tightly together

Question 39

What causes compaction?

Answer 39

E-Catherine cell adhesion protein

Question 40

How is the blastocoele formed?

Answer 40

From fluid appearing in blastomeres during cavitation, causing sodium and water to enter

Question 41

When does cavitation begin?

Answer 41

About four days after fertilization

Question 42

Describe hatching of the human embryo

Answer 42

Cells of the blastocyst secrete proteases Which digest the zone of proteins Causing the blast assist to hatch out of the Zona and the embryo escapes

Question 43

When does hatching occur?

Answer 43

Before implantation

Question 44

How is hatching related to infertility?

Answer 44

Inability to hatch is one cause of infertility

Question 45

What might cause an inability to hatch?

Answer 45

Altered ZP Absence of proteases

Question 46

What are the two reasons for the ZP being present during early cleavages?

Answer 46

Protect protection and to prevent immature embedding

Question 47

What does the ZP protect against?

Answer 47

Physical dangers and immuno responses

Question 48

What is the possible cause of ectopic pregnancies?

Answer 48

Premature hatching

Question 49

Where do the major majority of ectopic pregnancies occur?

Answer 49

In oviduct (96%)

Question 50

List the five implantation events

Answer 50

Apposition of blastocyst to endometrial epithelium Adherence of the blastocyst via solid adhesion molecules Formation of SYNCTIO trophoblast Penetration Decidual reaction

Question 51

What is the synctiotrophoblast?

Answer 51

A giant multinucleate cell that surrounds the complete embryo produced by the fusion of Cito tropho blast cells

Question 52

How does penetration occur?

Answer 52

Synctiotrophoblast is invasive and works its way into the uterine tissue

Question 53

What is the decidual reaction?

Answer 53

Uterine tissue responds to invasion by setting up an immunological barrier called the decidua