Fertilization and Gastrulation

Question 1

Step one in fertilization- capacitation

Answer 1

Glycoprotein coat and seminal plasma proteins removed from plasma membrane of sperm
Passage of sperm through corona radiata with help of hyaluronidase

Question 2

Step two in fertilization- penetration

Answer 2

Penetration of zona pellucida helped by releasing esterases, acrosin* and neuraminidase
Zona reaction helps to block polyspermy

Question 3

Step three fertilization

Answer 3

Fusion of plasma membranes of oocyte and sperm

Head and tail of sperm enter oocyte cytoplasm

Question 4

Step four fertilization

Answer 4

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

Question 5

Features of cleavage

Answer 5

Increase in cell number, decrease in cell size
Embryo size unchanged
Starts about 30 hours after fertilization
Morula development occurs at about day 3

Question 6

Blastocyst forms when

Answer 6

Days 5-7, and that is when implantation of the blastocyst into the uterus ocurs

Question 7

What type of stem cells are in inner cell mass

Answer 7

Embryonic stem cells- pluripotent

Question 8

Trophoblast

Answer 8

Gives rise to cytotrophoblast -Stem cell layer for placenta
Mitotically active
Releases early pregnancy factor so female body does not reject the cell as foregin

Question 9

Syncytiotrophoblast

Answer 9

Formed from cytotrophoblast
Release proteolytic enzymes
Chorionic gonadotropin hCG which is responsible for implantation and initial signal of pregnancy

Question 10

Hydatidiform mole and choriocarcinomas

Answer 10

Abnormal trophoblastic proliferation, excessive amounts of hCG produced
Complete mole results from fertilization of empty oocyte followed by duplication of sperm, or fertilization of empty oocyte by two sperm
Partial mole results from feralization of normal oocyte by two sperm
Can develop into malignant tumor

Question 11

Week 2 inner cell mass

Answer 11

Inner cell mass gives rise to:
Epiblast -gives rise to ectoderm, amnion and amniotic cavity
Hypoblast- gives rise to extraembryonic endoderm, prechordal plate, primary/secondary yolk sac, extraembryonic mesoderm

Question 12

Extraembryonic somatic mesoderm and extraembryonic splanchnic mesoderm

Answer 12

Somatic mesoderm lines the trophoblast/amnion (also forms connecting stalk (umbilical cord)When and chorion)
Splanchnic mesoderm lines the yolk sac (umbilical vesicle)- also forms primitive blood

Question 13

Placenta previa

Answer 13

Vaginal bleeding beyond 20 weeks gestation

Should prompt sonographic evaluation before digital vaginal examination

Question 14

Week 1-3: main events each week

Answer 14

Week 1- formation of inner cell mass
Week 2- formation of epiblast and hypoblast
Week 3- gastrulation (formation of 3 primary germ layer- ectoderm, mesoderm, endoderm), neurulation, formation of heart and circulatory system

Question 15

Notochord

Answer 15

Midline between ectoderm/endoderm. Comes from mesoderm
Extends from primitive node/knot at the top of the primitive streak anterior to prechordal plate
Template for vertebral column
Induces neural plate formation by releasing SHH
This all happens in the epiblast

Question 16

Formation of notochord plate

Answer 16

Cells forming notochord migrate from primitive pit in a cephalic direction
Lie between ectoderm and endoderm and form notochordal process
Notochordal process fuses with endoderm forming notochordal plate *amniotic cavity and primary yolk sac are in communication at this time
Notochordal cells round up and form notochord proper

Question 17

Chordomas

Answer 17

Rare slow growing aggressive neoplasms of bone
Arise from remnants of notochord
Occur in axial skeleton in spheno-occipital region of skull and sacral regions

Question 18

Allantois

Answer 18

Posterior midline
Diverticulum from wall of yolk sac
Endodermal structure
Template for umbilical arteries and vein
Becomes urachus which is attached to bladder

Question 19

Mesoderm derivatives

Answer 19

Paraxial–> Somites: muscle, skeleton, dermis
Intermediate–>Urogenital: kidneys, gonads
Lateral plate–> Connective tissue: blood, lymph, mesenteries, cardiovascular

Question 20

Embryonic ectoderm forms the

Answer 20

Neural crest

Question 21

Epiblast cells form

Answer 21

The actual embryo

Question 22

Fertilization occurs where

Answer 22

Ampulla of uterine tube which is the distal 2/3rds of the tube

Question 23

What is the corona radiata

Answer 23

Follicular cells from the ovary that surround the human ovum

Question 24

What is expelled at the end of fertilization

Answer 24

The second polar body

Question 25

When does cleavage occur

Answer 25

About 30 hours after fertilization

Question 26

When does formation of morula occur

Answer 26

About day 3, and at day 4 it enters the body of the uterus

Question 27

When does implantation occur

Answer 27

Starts about day 6

Question 28

Sacrococcegreal teratoma

Answer 28

Persistence of the primitive plate (in the caudal region)

Question 29

Oropharyngeal teratoma

Answer 29

Primordial germ cells have abnormal migration and migrate to oral region