Early embryonic development 1

Question 1

What is the ideal site of implantation for a zygote?

Answer 1

Posterior uterine wall

Question 2

How many weeks is the pre embryonic period?

Answer 2

Weeks 1-2

Question 3

How many weeks is the embryonic period?

Answer 3

Weeks 3-8

Question 4

How many weeks is the foetal period?

Answer 4

Weeks 9-38

Question 5

Define zygote

Answer 5

A fertilised ovum/oocyte

Question 6

Define cleavage

Answer 6

The dividing of cells into two masses known as blastomeres. First cleavage happens ~30 hours after fertilisation (resting period)

Question 7

Define zona pellucida

Answer 7

The glycoprotein ‘shell’ to prevent polyspermy

Question 8

Define morula

Answer 8

The result of cleavage of the fertilised oocyte, each cell is Totipotent

Question 9

Define ovary

Answer 9

The female reproductive organ producing oocytes/eggs for fertilisation

Question 10

Define fallopian tube

Answer 10

A tube the oocyte travels along to reach the uterus. The egg is fertilised at the ampulla of the fallopian tube.

Question 11

Define uterus

Answer 11

Female reproductive organ where implantation of the zygote and growth of the embryo occurs

Question 12

Define blastocyst

Answer 12

Formed from the compaction of cells that make up the morula

Question 13

Define tropoblast

Answer 13

(Outer cell mass) will later form support structures for the embryo (placenta)

Question 14

Define embryoblast

Answer 14

(Inner cell mass) will later become the bilaminar disk

Question 15

Define implantation

Answer 15

The attachment of the Blastocyst to the wall of the uterus at day 6 – 7

Question 16

Define cytotrophoblast

Answer 16

(Derivative of Trophoblast) Placental membrane around the yolk sac

Question 17

Define syncytiotrophoblast

Answer 17

(Derivative of Trophoblast) Cells that invade maternal sinusoids (irregular blood vessels) resulting in uteroplacental circulation.

Question 18

What is compaction?

Answer 18

Blastomeres which make the morula compact to form the blastocyst

Question 19

What is hatching?

Answer 19

Blastocyst hatches from the zona pellucida
Allows enlargement
Allows implantation

Question 20

What is implantation?

Answer 20

Interstitial

The uterine epithelium is breached and the conceptus implants within the uterine stroma.

Question 21

What does the embryoblast differentiate into?

Answer 21

Epiblast

Hypoblast

Question 22

What does the Trophoblast differentiate into?

Answer 22

Syncytiotrophoblast

Cytotrophoblast

Question 23

At early stages of development does the embryo or placenta have priority over development?

Answer 23

Placenta

Question 24

What are the implantation defects?

Answer 24

Ectopic pregnancy

Placenta praevia

Question 25

What is an ectopic pregnancy?

Answer 25

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

Question 26

What is placenta praevia?

Answer 26

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

Question 27

What is the embryonic pole?

Answer 27

Rapid development of Syncytiotrophoblast

Question 28

What is the Abembryonic pole?

Answer 28

Primitive yolk sac formed by Heuser’s membrane spreading across the Blastocyst cavity. Yolk sac membrane is in contact with the cytotrophoblast layer

Question 29

What is the acellular extraembryonic reticulum converted to by cellular migration?

Answer 29

extraembryonic mesoderm

Question 30

What happens in week 2 (day 11)?

Answer 30

Primitive yolk sac membrane is pushed away from the cytotrophoblast layer by an acellular extraembryonic reticulum.

Question 31

What happens in week 2 (day 12)?

Answer 31

Maternal sinusoids invaded by syncytiotrophoblast. Lacunae become continuous with sinusoids. Uteroplacental circulation begins. Uterine stroma prepares for support of the embryo.

Question 32

What happens in week 2 (day 13)?

Answer 32

Formation of secondary yolk sac Pinches off from the primary yolk sac A.k.a. Definitive yolk sac

Question 33

What forms the Chorionic cavity?

Answer 33

Spaces within the extraembryonic mesoderm merge

Question 34

What happens in week 2 (day 14)?

Answer 34

The Connecting Stalk suspends the embryo and its cavities in the chorionic cavity. The connecting stalk is a column of mesoderm, and is the future umbilical cord.

Question 35

What can be confused with menstrual bleeding at the end of week 2?

Answer 35

Bleeding around now can be confused with menstrual bleeding.

Question 36

What has happened by the end of week 2?

Answer 36

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