Bilaminar

Question 1

Acrosome Reaction

Answer 1

Upon contact with the corona radiata, the overlying plasma membrane of the acrosome becomes unstable as a glycoprotein coat and seminal plasma proteins are removed from the plasma membrane

Question 2

Cortical Reaction

Answer 2

• Prevents polyspermy
• Triggered by acrosome reaction
• Oocyte membrane becomes impenetrable to other sperm

Question 3

Zona reaction

Answer 3

• prevents polyspermy
• triggered by acrosome reaction
• Zona Pellucida alters its structure o prevent other sperm binding and penetration

Question 4

List the steps to fertilization

Answer 4

1. Acrosome reaction
2. Fusion of plasma membranes of sperm and oocyte
3. Formation of male pronucleus
4. Completion of second meiotic division of oocyte
5. Fusion of pronuclei to form diploid zygote

Question 5

Syngamy

Answer 5

Fusion of male and female pronuclei to form a diploid zygote

Question 6

Results of zygote cleavage

Answer 6

• mitotic divisions produce cells called blastomeres
• cells become smaller with each division (still contained within ZP)
• cells arranged in loose clump until 8 cell stage when compaction begins to take place

Question 7

Compaction

Answer 7

• at 8 cell stage, blastomeres begin to maximize their contact with each other, forming a ball of cells held together by tight junctions

Question 8

Morula

Answer 8

• “Mulberry”
• dense 16 to 32 cell ball comprised of inner cell mass and outer cell mass
• forms at ~3 days

Question 9

What does the morula form?

Answer 9

• After ~4 days, the morula enters the uterus
• The fluid from the uterus begins to penetrate the ZP into the intercellular spaes of the inner cell mass
• now called a blastocyst

Question 10

Trophoblast

Answer 10

• derived from outer cell mass of morula

- differentiates into two layers: cytotrophoblast and synctiotrophoblast

Question 11

cytotrophoblast

Answer 11

• inner layer of mononucleated cells with mitotic capacity

- derived from trophoblast at ~8 days

Question 12

synctiotrophoblast

Answer 12

• Outer multinucleated zone of the trophoblast
• over the embryoblast
• invades the uterine endometrium to implant the blastocyst
• derived from trophoblast at ~day 8

Question 13

embryoblast

Answer 13

-derived from inner cell mass of blastocyst at 4-5 days

Question 14

What are the 2 layers of the embryoblast?

Answer 14

• epiblast and hypoblast

- differentiates at ~ day 8

Question 15

epiblast

Answer 15

• dorsal layer of the embryonic disc
• site of formation of amniotic cavity
• cells adjacent to the cavity form the amnion and are individually called amnioblasts

Question 16

hypoblast

Answer 16

• ventral layer of embryonic disc
• at day 9, thin layer of cells from the hypoblast (Exocoelomic membrane) migrate along inner surface of cytotrophoblast to form the primitive yolk sac (exocoelomic cavity)

Question 17

Why is hatching of the blastocyst important?

Answer 17

• Allows for growth of the blastocyst

- allows for implantation into the uterine endometrium

Question 18

What produces hCG during week 2 of pregnancy?

Answer 18

• synctiotrophoblast takes over at week 2
• hCG enters meternal bloodstream via trophoblastic lacunae
• stimulates progesterone production by corpus luteum
• without hCG at this stage, menstruation occurs

Question 19

What takes over production of hCG at week 8?

Answer 19

The placenta

Question 20

Lacunae

Answer 20

• “lakes”
• form within synctiotrophoblast at ~9 days
• contain hCG and anastomose with maternal sinusoids, initiating uteroplacental circulation

Question 21

Where and how do the amniotic cavity develop?

Answer 21

• first develops from clefts in the epiblast after 8 days

- cells surrounding the amniotic cavity become amniblasts and together form the amnion

Question 22

Where and how do the Chorion and Chorionic cavity develop?

Answer 22

• Chorion has origins in extraembryonic mesoderm, which prolifereates between the exocoelomic membrane and the cytotrophoblast at day 10-11
• cavities form within the extraembryonic mesoderm, forming the chorionic cavity (aka extraembryonic coelom)

Question 23

Chorionic plate

Answer 23

• 3 layers: (from deep to superficial)
  1. extraembryonic mesoderm
  2. cytotrophoblast
  3. synctiotrophoblast

Question 24

Primary chorionic villi

Answer 24

• projections that proliferate from the cytotrophoblast into the surrounding synctiotrophoblast
• grow out into the lacunae, bringing a surrounding layer of synctiotrophoblast
• happens in conjunction with anastomosis of maternal sinusoids with trophoblastic lacunae

Question 25

secondary villi

Answer 25

• primary villi become secondary in week 3 when extraembryonic mesodermal cells proliferate into the center of the primary villi

Question 26

tertiary villi

Answer 26

• by the end of week three, extraembryonic mesodermal cells within the secondary villi differentiate into blood vessels, forming tertiary villi

Question 27

Primary Yolk Sac

Answer 27

• aka exocoelomic cavity

- initially formed on day 9 as exocoelomic membrane grows from hypoblast along inside surface of cytotrophoblast

Question 28

Secondary Yolk Sac

Answer 28

• aka definitive yolk sac
• cells originating in ypoblast migrate along inner surface of primay yolk sac to form a new, smaller cavity
• large protions of the primary yolk sac are pinched off, left to become exocoelomic cysts which degrade within the chorionic cavity

Question 29

Connecting stalk

Answer 29

• aka body stalk
• formed from extraembryonic mesoderm at caudal an of embryo at day 13
• develops into umbilical cord with formation of blood vessels and initiation of uteroplacental circulation

Question 30

Capacitation

Answer 30

Functional changes that sperm undergo in the female reproductive tract that enable them to fertilize a secondary oocyte
-must be able to pass through zona pellucida and corona radiata