Embryology: Fertilization

Question 1

Gametogenesis

Answer 1

Production of gametes (oocytes and spermatozoa)

Question 2

Location of Fertilization

Answer 2

Uterine tubes, first 1/3 (lateral)

Question 3

Purpose of Corona Radiata in Fertilization

Answer 3

Keep ovum from planting where it shouldn’t, control sperm. Implantation is ideally done in the endometrium in uterus.

Question 4

Restriction event

Answer 4

Changing a cell from one type to another, definitive, rate limiting step

Question 5

Zona Pellucida – Cortical Reaction

Answer 5

Zona Pellucida has sperm receptors that recognize integral proteins of sperm PM

Question 6

Polyspermy

Answer 6

Fertilization by more than one sperm

Question 7

Acrosome (of sperm)

Answer 7

Head of sperm that contains hydrolytic enzymes used to breakdown zona pellucida

Question 8

Stages of Fertilization (2)

Answer 8

1. Penetrate corona radiata
2. Sperm bind to and penetrate zona pellucida

**Acrosome reaction follows to prevent polyspermy

Question 9

Cortical Reaction (2 stages)

Answer 9

1. Fast component: change in resting potential of oocyte (prevent binding of sperm)
2. Slow component: release of cortical granules (destroy sperm receptors, ZP3)

Question 10

ZP3 removal prevents sperm-egg binding and fertilization

Answer 10

Results in infertility

Question 11

Izumo

Answer 11

Protein required for sperm to fuse with eggs

Question 12

Monozygotic Twins vs. Dizygotic Twins

Answer 12

1. Monozygotic Twins = Identical, same sex. Occurs when fertilized egg splits into two.
2. Dizygotic Twins = Fraternal. Two separate eggs are fertilized.

Question 13

Polar Twins (Half-Identical)

Answer 13

Happens with egg splits before fertilization and polar body is also fertilized by different sperm.

Resultant twins share half genes in common. Assumes polar body has enough material to last through implantation.

Question 14

Females are always mosaics

Answer 14

Mosaicism – cells within one individual have different genetic makeup, results from mitotic error

Blaschko’s lines

Question 15

Chimera

Answer 15

Genetically different cells, different zygotes (started as two separate people, ended as one)

Question 16

Mosaics vs. Chimera

Answer 16

Both contain genetically different cells, mosaic comes from one zygote. Chimera comes from two different zygotes.

Question 17

Lyonization

Answer 17

Random X-chromosome inactivation

Question 18

Blastomeres

Answer 18

Beginning mitotic division of gametes, totipotent

Question 19

Ectopic pregnancy

Answer 19

Is implantation of embryo anywhere other than endometrial lining of uterus

Question 20

Restriction event in implantation

Answer 20

Transition from morula to blastocyst – two cell types, epiblasts and trophoblasts (pluripotent)

Question 21

Zona pellucida dissipates at the start of implantation

Answer 21

Only need it until embryo is implanted at correct location

Question 22

Hatching of Human Embryo

Answer 22

Blastocyst must secrete proteases to digest zona pellucida and implant onto endometrium

Question 23

Embryonic stem cell source

Answer 23

Inner cell mass (from blastocyst)

Question 24

Components of blastocyst

Answer 24

1. Inner cell mass (embryoblast)
2. Outer cell mass (trophoblast)
3. Blastocoele (cavity)

Need both embryoblasts and trophoblasts to make a fetus

Question 25

Embryoblast

Answer 25

Eventually creates embryo, differentiates to hypoblast and epiblast

Question 26

Trophoblast

Answer 26

Eventually becomes placenta, differentiates to cytotrophoblast and syncitiotrophoblast

Question 27

Totipotent stem cells

Answer 27

Have potential to grow into an entire organism

Question 28

Pluripotent stem cells

Answer 28

Cannot grow into an entire organism but can derive any of the three germ layers

Question 29

Twinning

Answer 29

1. Cleavage of early embryo
2. Splitting of ICM
3. Incomplete division of ICM (conjoined siamese twins)

Question 30

Parasitic twin (craniopagus parasiticus)

Answer 30

Incomplete twin grows, not functional organism.

Question 31

Fetus in fetu

Answer 31

Inclusion twinning, fetus gets trapped and grows inside of its twin. Is a living entity because it is attached to host.