Fertilization and Gastrulation

Question 1

Anatomy of the Human Ovum (5)

CZNPP

Answer 1

1. Corona radiata
2. Zona pellucida
3. Nucleus
4. Perivitelline space
5. Plasma membrane

Question 2

Corona radiata

Answer 2

Outermost layer of cells. Helps provide nutrients to the nucleus and must be penetrated by the sperm.

Question 3

Zona pellucida

Answer 3

Glycoprotein layer surrounding the plasma membrane. If the egg is fertilized, the zona pellucida will disappear and allows implantation in the uterus.

Question 4

Perivitelline space

Answer 4

Space between the zona pellucida and cell membrane.

Question 5

Anatomy of the Human Sperm

Answer 5

Head: acrosome and nucleus.
Neck
Tail: middle, principle and end piece.

Question 6

Acrosome

Answer 6

Contains enzymes (hyaluronidase and acrosin) which break down the zona pellucida.

Question 7

Step 1 of Fertilization

Answer 7

Capacitation: glycoprotein coat and seminal proteins removed from PM of sperm.
Passage of sperm through the corona radiata via hyaluronidase.

Question 8

Step 2 of Fertilization

Answer 8

Penetration of zona pellucida (via enzymes: esterases, acrosin, neuroamidase).
Zona reaction - block to polyspermy.

Question 9

Step 3 of Fertilization

Answer 9

Fusion of PMs of oocyte and sperm.

Head and tail of sperm enters oocyte cytoplasm.

Question 10

Step 4 of Fertilization

Answer 10

Completion of second meiotic division.
Formation of male pronucleus.
Fusion of male and female pronuclei.

Question 11

Results of Fertilization (5)

Answer 11

1. Completion of 2nd meiotic division.
2. Restoration of diploid number of chromosomes.
3. Determination of sex of embryo.
4. Metabolic activation of oocyte.
5. Initiation of cleavage.

Question 12

Cleavage (4)

Answer 12

1. Increase in cell number.
2. Decrease in cell size.
3. Embryo size unchanged.
4. Morula development.

Question 13

Blastocyst after Week 1

Answer 13

Now a “late blastocyst”. Enlargement of blastocyst cavity, Degradation of zona pellucida. “Stretching” of trophoblast layer.

Question 14

Assisted Reproductive Technologies (3)

Answer 14

1. In vitro fertilization and embryo transfer.
2. Cryopreservation of embryo.
3. Intracytoplasmic sperm injection.

Question 15

Early Pregnancy Factor

Answer 15

A pregnancy-dependent, suppressor-releasing hormone. A link between fertilization and immunomodulation.

Question 16

Cryotrophoblast

Answer 16

Stem cell layer.

Mitotically active.

Question 17

Syncytiotrophoblast

Answer 17

Contains proteolytic enzymes, chorionic gonadotropin.

Responsible for implantation and initial signal of pregnancy.

Question 18

Hyatidiform Mole

Answer 18

Abnormal trophoblastic proliferation; excess amounts of hCG made.

Question 19

Complete Hyatidiform Mole results from:

Answer 19

Fertilization of an empty oocyte, followed by duplication of sperm OR from fertilization of an empty oocyte by 2 sperm.

Question 20

Partial Hyatidiform Mole results from:

Answer 20

Fertilization of a normal oocyte by two sperm.

Question 21

Clinical features of Hyatidiform Mole

Answer 21

Vaginal bleeding
Pelvic pain
Enlarged uterus
Hyperemesis gravidarum (severe nausea in pregnancy)

Question 22

Choriocarcinomas

Answer 22

Malignant tumor which develops from Hyatidiform Mole.

Question 23

Blastocyst after Week 2

Answer 23

Inner cell mass forms.

• Epiblast: ectoderm, amnion and amniotic cavity.
• Hypoblast

Question 24

Hypoblast

Answer 24

Gives rise to endoderm, prechordal plate, primary and secondary yolk sac, and extraembryonic mesoderm.

Question 25

Components of Extraembryonic Mesoderm (3)

Answer 25

1. Extraembryonic coelem
2. Extraembryonic somatic mesoderm
3. Extraembryonic splachnic mesoderm

Question 26

Extraembryonic coelem

Answer 26

Hollow cavity outside of the embryo.

Question 27

Extraembryonic Somatic Mesoderm

Answer 27

Lines the trophoblast and covers the amnion.

Question 28

Extraembryonic Splanchnic Mesoderm

Answer 28

Lines the yolk sac (umbilical vesicle).

Question 29

Derivatives of EEM (3)

Answer 29

1. Connecting stalk
2. Primitive blood
3. Chorion

Question 30

Connecting Stalk

Answer 30

EE somatic mesoderm.
Forms at embryonic pole.
Position changes during develoment.

Question 31

Primitive Blood

Answer 31

EE splanchnic mesoderm.

Forms in the wall of the yolk sac.

Question 32

Chorion

Answer 32

EE somatic mesoderm.

Cytotrophoblast and Syncytiophoblast.

Question 33

Placenta Previa

Answer 33

Vaginal bleeding beyond 20 wks gestation.
Antepardum bleeding should prompt sonographic eval before digital vaginal exam (palpitation of placenta can cause hemorrhage).

Question 34

Overview of Weeks 1-3

Answer 34

Week 1: formation of the inner cell mass.
Week 2: formation of epiblast and hypoblast.
Week 3: gastrulation.

Question 35

Gastrulation

Answer 35

Formation of 3 germ layers and primitive streak.

Question 36

Components of Primitive Streak (3)

Answer 36

Primitive knot (node)
Primitive groove
Primitive pit

Question 37

Notochord

Answer 37

The midline.
Extends from primitive knot anterior to prechordal plate.
Template for vertebral column.
Induces neural plate.

Question 38

Chordomas

Answer 38

Rare and slow growing aggressive neoplasms of bone.

Arise from remnants of notochord.

Question 39

Allantois

Answer 39

Posterior midline.
Diverticulum from wall of yolk sac.
Endoderm.
Template for umbilical arteries and veins –> becomes urachus.

Question 40

Components of Mesoderm (3)

Answer 40

Paraxial: Somites (muscle, vertebral skeleton, dermis).
Intermediate: urogenital.
Lateral plate: connective tissues.