Early Embryology

Question 1

Development of human being:

Answer 1

Fertilisation
            |
Single cell
            |
Ball of cells
            |
Cavities + two layered disc
            |
Three layered disc with middle layer
            |
Segments in middle layer + tubes form from two outer layers
            |
Fully formed body

Question 2

Where does fertilisation occur?

Answer 2

Ampulla of uterine tube within 12 hours of ovulation

Question 3

What happens in fertilisation?

Answer 3

Reduction divisions (oocyte) completed

Restores diploid number of chromosomes (46)

Genetic sex determined

Question 4

What type of cells are sperm and ovum?

Answer 4

Haploid (23 chromosomes)

Question 5

What happened within 36 hours of fertilisation?

Answer 5

Initiation of cleavage

Question 6

What essentially is the acrosome reaction?

Answer 6

Regulated exocytosis

Enables penetration of zona pellucida

Question 7

How is acrosome reaction triggered?

Answer 7

Sperm penetrates corona radiata (hyaluronidase)

Interacts with ZP3 receptor

Question 8

What happens during acrosome reaction?

Answer 8

Sperm digests zona pellucida

Sperm and oocyte membrane fusion

Question 9

What happens after sperm fuses with oocyte?

Answer 9

Completion of oocyte meiosis

Release of nucleus into oocyte cytoplasm

Question 10

What happens to prevent second entry of sperm into oocyte?

Answer 10

Cortical granules release content to degrade ZP3

Increase in oocyte membrane negative charge

Question 11

What happens in 1st week of development?

Answer 11

Ovulation to implantation

Question 12

What happens in donation of healthy mitochondria?

Answer 12

Parent’s nucleus removed and kept

Donor nucleus removed and destroyed

Parent’s nucleus placed inside donor egg

Question 13

What happens to zona pellucida in first week of development?

Answer 13

Remains intact

Question 14

Mitosis in first week of development:

Answer 14

Maternal and paternal chromosomes line up on spindle equator

Chromatids separate

Question 15

What doesn’t happen in first week of development?

Answer 15

Cell growth - as only division in same volume

Question 16

When does initiation of cleavage occur?

Answer 16

Within 36 hours of fertilisation

Question 17

Early cleavage:

Answer 17

Cell division without growth (inside zona pellucida)

Question 18

When does compaction cleavage begin?

Answer 18

At 8 cells - central cells linked by gap junctions

Become more like a homogenous ball

Anterior/posterior axis of embryo established

Question 19

What’s a Morula?

Answer 19

16+ cells

Inner and outer layers

Question 20

What happens to morula?

Answer 20

Transported along uterine tube to uterus

Zona pellucida disappears

Question 21

What happens to outer cells on morula?

Answer 21

Divide to become trophectoderm (trophoblast) and inner cells (inner cell mass)

Question 22

What happens at 4.5 days?

Answer 22

Cavities form in inner cell mass

Blastocyst unattached to uterus

Question 23

What’s a blastocyst?

Answer 23

Trophoblast and inner cell mass

Question 24

What happens at 5-6 days in genetic testing?

Answer 24

Trophectoderm sampled

Question 25

What happens at 5.5 - 6 days?

Answer 25

Blastocyst binds to uterus epithelium Embryonic pole attaches

Question 26

How does blastocyst bind to uterus wall?

Answer 26

Down regulation of anti-adhesion molecule MUC-1 Allows binding via selectins to glyco-compartments on epithelial cells (uterus)

Question 27

What molecules are involved in binding of blastocyst to uterine wall?

Answer 27

Integrins, laminin and fibronectin

Question 28

What happens at 6-7 days?

Answer 28

Implantation of blastocyst starts

Question 29

What happens during implantation of blastocyst?

Answer 29

Trophoblast becomes invasive Scynctiotrophoblast multinucleate synctium invades via metalloproteases

Question 30

What does blastocyst implantation cause?

Answer 30

Immunosuppressive of host/graft and graft/host reactions

Question 31

What happens on day 8?

Answer 31

More embedding of blastocyst into uterine wall

Question 32

What happens to trophoblast on day 8?

Answer 32

Divides into synctiotrophoblast and cytotrophoblast

Question 33

What happens to embryo on day 8?

Answer 33

Two layers form - epiblast and hypoblast Amniotic cavity (space)begins to form within epiblast.

Question 34

What coats blastocyst cavity?

Answer 34

Hypoblast cells - on day 9

Question 35

What becomes primary yolk sac?

Answer 35

Blastocyst cavity

Question 36

What happens on day 9?

Answer 36

Form primary yolk sac Spaces develop within synctiotrophoblast Formation of amniotic cavity

Question 37

What is formed deep to trophoblast following day 9?

Answer 37

Extraembryonic mesoderm

Question 38

Does the embryonic disc have layers?

Answer 38

Two layers

Question 39

What happens on days 11-12?

Answer 39

Blastocyst burrows completely into endometrium Synctiotrophoblast cells erode through walls of large maternal capillaries

Question 40

What causes primitive placenta circulation?

Answer 40

Days 11-12 Synctiotrophoblast cells erode through large maternal capillary walls + bleed into spaces

Question 41

What new layer is formed in days 11-12?

Answer 41

Between yolk sac and cytotrophoblast

Question 42

What are spaces formed in, in days 11-12?

Answer 42

Extra embryonic mesoderm

Question 43

What’s the chronic in cavity formed by?

Answer 43

Fusion of spaces in extra embryonic mesoderm (days 11-12)

Question 44

What two layers develop in trophoblast at the end of week 2?

Answer 44

Synctiotrophoblast Cytotrophoblast

Question 45

What 2 layers form in the inner cell mass at the end of week 2?

Answer 45

Epiblast - ectoderm Hypoblast - endoderm

Question 46

What two cavities form at the end of week 2?

Answer 46

Amniotic cavity Chorionic cavity

Question 47

What’s preeclampsia?

Answer 47

Features maternal hypertension and proteinuria after 20 weeks

Question 48

Where’s the most common site of ectopic pregnancy?

Answer 48

Ampulla - results in tube rupture + blood loss

Question 49

What environmental causes of malformations are there?

Answer 49

Drugs/chemicals Infectious agents Ionising radiation

Question 50

What determines dorsal-ventral axes in embryo?

Answer 50

Oocyte - but unclear mechanisms

Question 51

What determines left right axes in embryo?

Answer 51

Cilia movement (tend to be one direction) in node

Question 52

What axes are there in the embryo?

Answer 52

Dorsal-ventral Left-right Rostral caudal