Development of Embryo

Question 1

How were nutrients provided before placental circulation?

Answer 1

Diffusion from uterine gland

Question 2

How are syncytiotrophoblasts involved in delivering of nutrients?

Answer 2

• Encroach on uterine lining and can get nutrients from mother
• Pass out excretion products from embryo back to uterine gland

This can only happen for a short while before more nutrients are needed

Syncytiotrophoblasts then break down wall of maternal capillary to establish uteroplacental circulation

Question 3

What are gaps between syncytiotrophoblasts called?

Answer 3

Trophoblastic lacuna

Question 4

What is function of trophoblastic lacuna?

Answer 4

Where nutrients are held before reaching embryo - blood seeps into these gaps before passing to developing embryo

Question 5

What is purpose of uteroplacental circulation?

Answer 5

Allows further development of embryo by developing circulation between mother & embryo

Question 6

When does uteroplacental circulation occur?

Answer 6

4 weeks from last period - can cause spotting (mistaken for period if unaware of pregnancy)

Question 7

What is the extraembryonic mesoderm?

When does it form?

Answer 7

New layer of connective tissue derived from yolk sac cells. Forms between 1ary yolk sac and cytotrophoblast

Forms 10-11 & 11-12 days

Question 8

What is purpose of extraembryonic mesoderm?

Answer 8

Engulfs all of developing embryo. Eventually develops to cover amniotic cavity too

Question 9

When and where does chorionic cavity form?

Answer 9

Forms in extraembryonic mesoderm. 12-13 days

Question 10

What is purpose of chorionic cavity?

Answer 10

Migrates to surround embryo

Question 11

How is the definitive yolk sac formed?

Answer 11

2nd wave of hypoblast cells migrate to form a 2ary (definitive) yolk sac

Question 12

What does the definitive yolk sac cause?

Answer 12

Pushes 1ary yolk sac away from embryo. Eventually pinches off due to weight of chronic cavity –> left with tiny remnants

Question 13

How are amniotic cavity and definitive yolk sac suspended in chorionic cavity?

Answer 13

By connecting stalk

Question 14

What is purpose of connecting stalk?

Answer 14

Connects embryo to uterine lining. Stalk becomes part of umbilical cord in future (contains umbilical artery and vein)

Question 15

By the end of week 2, what are the major changes that the embryo has undergone?

Answer 15

1. Bilaminar disc - Epiblast and hypoblast cells. In between amniotic cavity and definitive yolk sac
2. Fully implanted
3. Established uteroplacental circulation
4. Blastocyst cavity –> 1ary yolk sac –> definitive yolk sac
5. Amniotic cavity
6. Chorionic cavity