Session 1

Question 1

Describe the process of fertilisation

Answer 1

1) Oocyte (female gamete) is released from the ovary
2) It travels along the Fallopian (uterine) tube
3) It Is fertilized by sperm in the ampulla

Question 2

Define the pre embryonic, embryonic and foetal periods of human development

Answer 2

Pre embryonic: weeks 1 and 2

Embryonic: 3 to 8

Foetal: after 8

Question 3

Summarise the changes that occur at end of week 1

Answer 3

1) Compaction of blastomeres to form blastocyst
2) Hatching blastocyst detaches from Zona Pellucida, so blastocyst can implant in uterine surface
3) Implantation can occur.

Question 4

What changes have occurred by the end of the second week?

Answer 4

1) The conceptus has implanted
2) The embryo and its two cavities (Amniotic cavity and Yolk sac) are suspended by a connecting stalk in a supporting Sac (Chorionic Cavity)

Question 5

Discuss some implantation defects

Answer 5

Ectopic Pregnancy – Implantation at site other than uterine body (most commonly fallopian tube). Can quickly become a life-threatening emergency.

Placenta Praevia – Implantation in lower uterine segment. Placenta grows across cervical opening. Requires C-section delivery

Question 6

Describe Step 1 of the changes that occur in the second week

Answer 6

Embryoblast differentiates into Epiblast and Hypoblast (bilaminar disc)

Question 7

Describe Step 2 of the changes that occur in the second week

Answer 7

Trophoblast differentiates into Syncytiotrophoblast (which invade maternal sinusoids) at embryonic pole and Cytotrophoblast at the abembryonic pole

Question 8

Describe Step 3 of the changes that occur in the second week

Answer 8

Amniotic cavity formed.

Question 9

Describe Step 4 of the changes that occur in the second week

Answer 9

Heuser’s membrane spreads across the Blastocyst cavity forming the primitive yolk sac. Yolk sac membrane is in contact with the cytotrophoblast layer.

Question 10

Describe Step 5 of the changes that occur in the second week

Answer 10

Primitive yolk sac membrane is pushed away from the cytotrophoblast layer by an acellular extraembryonic reticulum. Reticulum is later converted to extraembryonic mesoderm by cell migration

Question 11

Describe Step 6 of the changes that occur in the second week

Answer 11

Uterine stroma prepares for support of the embryo

Question 12

Describe Step 7 of the changes that occur in the second week

Answer 12

Formation of definitive yolk sac which pinches off from the primary yolk sac

Question 13

Describe Step 8 of the changes that occur in the second week

Answer 13

Spaces within the extraembryonic mesoderm merge to form the chorionic cavity. Bleeding around now can be confused with menstrual bleeding.