Embryology weeks 1 and 2

Question 1

Where is the oocyte fertilised by the sperm?

Answer 1

In the ampulla of the Fallopian tube

Question 2

What is cleavage?

Answer 2

The first mitotic division of the zygote, resulting in 2 blastomeres

Question 3

What is the zone pellucida

Answer 3

It is the glycoprotein ‘shell’ that one sperm will be successful in penetrating. It protects but also restricts growth

Question 4

What is meant by the terms Totipotent, Pluripotent, Multipotent and Unipotent?

Answer 4

TOTIPOTENT cells have the ability to form any type of cell
PLURIPOTENT cells can become any type of cell except placenta cells
MULTIPOTENT cells can differentiate into a few different types opposite cell eg stem cells found in bone marrow can form red and whit blood cells
UNIPOTENT cells can only differentiate into one type of cell

Question 5

What is PGD?

Answer 5

Pre-implantation genetic diagnosis means that a cell can be safely removed from the morula and tested for serious inheritable genetic diseases so that only healthy embryos are transferred into the uterus.

Question 6

What happens in week 1 compaction?

Answer 6

First cavity forms

Blastocyst formation

Question 7

What occurs in week 1 hatching?

Answer 7

Blastocyst hatches from zone pellucida so it is free to enlarge. It can now interact with the uterine surface to implant

Question 8

What is the multinucleated sheet called that forms in week 2?

Answer 8

Synctiotrophoblast

Question 9

What happens during compaction?

Answer 9

The 8 cell or 16 cell embryo changes shape to form the morula. The first cavity is formed during compaction- the blastocyst.

Question 10

What is hatching and why must it occur?

Answer 10

It is when the blastocyst (an embryo pre-implantation day5/6) hatches from the zone pellucida meaning it is free to grow and can now interact with the uterin epithelium so implantation can occur

Question 11

Where is the ideal site for implantation?

Answer 11

The posterior uterine wall

Question 12

What happens during implantation?

Answer 12

The embryo breaches the uterine epithelium to interact with the uterine stroma. This means implantation is interstitial. Implantation establishes maternal blood flow to the placenta. It also establishes the basic structural unit of materno-fetal exchange- the chorionic villus

Question 13

What does the trophoblast go on to form?

Answer 13

The outer cell mass which is split into

The Syncytiotrophoblast and the Cytotrophoblast

Question 14

What makes up the bilaminar disk?

Answer 14

Epiblast
Hypoblast
Amniotic cavity

Question 15

What does the epiblast go on to form?

Answer 15

The embryo

Question 16

What does the extra embryonic reticulum do and then go on to form?

Answer 16

The acellular extra embryonic reticule pushes the primitive yolk sack away from the cytotrophblast

Question 17

What are lacunae? Why are they important?

Answer 17

They are spaces in the syncytiotrophoblast formed when maternal sinusoids invade. This is when uteroplacental circulation begins

Question 18

How is the secondary yolk sac formed?

Answer 18

The primary yolk sack pinches off and small segment becomes the secondary yolk sac

Question 19

How is the chorionic cavity formed??

Answer 19

Spaces within the extraembryonic mesoderm merge to form a cavity known as the chorionic cavity

Question 20

What is an ectopic pregnancy? Why can it be life-threatening?

Answer 20

When implantation occurs not In the uterine body most commonly in the Fallopian Tube. It can quickly become life threatening as the Fallopian tube could rupture causing internal bleeding

Question 21

What is placenta praevia?

Answer 21

Implantation in the lower uterine segment. The placenta blocks the birth canal so c section is necessary. It can become life threatening