Embryology: Weeks 1-3

Question 1

What is fertilisation?

Answer 1

Process by which sperm and egg join together

Question 2

How long after fertilisation does the first cell division of the fertilised oocyte occur?

Answer 2

~30 hours

Question 3

What are blastomeres?

Answer 3

First cells of the dividing fertilised oocyte

Created within first 4 cell divisions

Question 4

What is a morula?

Answer 4

Collection of cells formed when cell division of the fertilised oocyte has produced 16 cells

Question 5

What is the blastocoel?

Answer 5

Reorganisation of morula to form blastocyst cavity

Question 6

What is a blastocyst?

Answer 6

Structure of cells once morula reorganises to form blastocyst cavity

Question 7

When does the blastocyst form?

Answer 7

Within first week of fertilisation

Question 8

What is the trophoblast?

Answer 8

Outer cell mass of blastocyst

Contacts with endometrium of uterus to facilitate implantation and formation of placenta

Question 9

What is the embryoblast?

Answer 9

Inner cell mass of blastocyst

Forms embryo itself

Question 10

During the second week after fertilisation, into what does the trophoblast divide?

Answer 10

Synctiotrophoblast

Cytotrophoblast

Question 11

During the second week after fertilisation, into what does the embryoblast divide?

Answer 11

Epiblast
Hypoblast
These two elements form bilaminar disk

Question 12

Within which cell structure of the developing embryo does the amniotic cavity form?

Answer 12

Epiblast

Question 13

Which cell structure of the embryo becomes continuous with the uterus during the process of implantation?

Answer 13

Synctiotrophoblast

Question 14

How does the uteroplacental circulation form during implantation of the embryo?

Answer 14

Sinusoids of maternal blood vessels invade lacunae of synctiotrophoblast

Question 15

When does gastrulation occur?

Answer 15

During 3rd week of embryonic development

Question 16

What is gastrulation?

Answer 16

Bilaminar disk becomes three germ cell layers and body axes develop

Question 17

Which cell type within the bilaminar disk undergoes gastrulation?

Answer 17

Epiblast

Question 18

What is the primitive streak?

Answer 18

Groove in midline of epiblast which appears during 3rd week of embryonic development
Largely controls gastrulation

Question 19

Where is the primitive node?

Answer 19

At cranial end of primitive streak

Question 20

What structure is within the primitive node?

Answer 20

Primitive pit

Question 21

What is the role of the primitive pit in gastrulation?

Answer 21

Epiblast cells break off and migrate towards primitive pit

Detach here and penetrate through epiblast layer to form germ cell layers

Question 22

What are the three germ cell layers?

Answer 22

Endoderm
Mesoderm
Ectoderm

Question 23

What forms the endoderm?

Answer 23

Epiblast cells that migrate through primitive pit and displace hypoblast cells

Question 24

What forms the mesoderm?

Answer 24

Epiblast cells that migrate through primitive pit and lie between epiblast layer and endoderm

Question 25

What forms the ectoderm?

Answer 25

Epiblast cells that remain in position

Question 26

What structures are derived from the endoderm?

Answer 26

Epithelial lining of digestive and respiratory tracts Lining of urethra, bladder, and reproductive system Liver Pancreas

Question 27

What structures are derived from the mesoderm?

Answer 27

Notochord Musculoskeletal system Muscular layer of stomach, intestine, etc Circulatory system

Question 28

What structures are derived from the ectoderm?

Answer 28

Epidermis of skin Cornea and lens of eye Nervous system