Embryonic Development

Question 1

Where does fertilization occur?

Answer 1

Ampulla of the uterine (fallopian) tube

Question 2

How is genetic sex determined?

Answer 2

1- Oocyte carrying X chromosome
2- Sperm may carry X or Y chromosome
3- XX: female
4- XY: male

Question 3

What processes occur during the first week of development?

Answer 3

Ovulation to implantation
1- Ovulation of haploid oocyte
2- Sperm penetrates oocyte wall
3- Fertilised oocyte implants on uterine wall

Question 4

What is the acrosome reaction?

Answer 4

1- Process sperm must go through to penetrate the female egg
2- Sperm penetrates corona radiata and zona pellucida by releasing enzymes
3- Sperm fuses with egg and releases its contents
4- Female pronucleus and male pronucleus fuse

Question 5

What types of RNA does the egg cytoplasm contain?

Answer 5

1- Mitochondrial DNA

2- Maternal mRNA

Question 6

When does the first mitosis begin?

Answer 6

After fertilisation

Question 7

When is cleavage initiated?

Answer 7

Within 36 hours of fertilisation

Question 8

What is a morula?

Answer 8

1- Early stage embryo, 3-4 days post fertilisation
2- 16+ cells
3- Solid ball of cells with inner and outer layers
4- Travels along fallopian tube and arrives at uterus 30-40 cells, 3-4 days post fertilisation
5- Zona pellucida intact until time for implantation
6- Outer cells divide to become trophectoderm
7- Some inner cells are trapped and become inner cell mass

Question 9

Why must the zona pellucida disappear?

Answer 9

For implantation on uterine wall

Question 10

Up to what stage are cells totipotent?

Answer 10

Blastocyst stage

Question 11

What is a blastocyst?

Answer 11

1- Early embryo
2- 4-5 days post fertilisation
3- Contain trophectoderm which is outer layer of trophoblast cells
4- Contain inner cell mass which are inner layer of cells
5- Still free and unattached in the uterus

Question 12

Which cells are removed for genetic testing in the early embryo?

Answer 12

5-6 days trophectoderm

Question 13

When does the embryo bind to the uterus wall?

Answer 13

5.5 to 6 days post fertilisation

Question 14

What part of the embryo binds to the uterus wall?

Answer 14

Embryonic pole

Question 15

How does the embryo bind to the uterus wall?

Answer 15

1- Via the embryonic pole
2- MUC-1, anti-adhesion molecule, is suppressed or down regulated
3- This allows the binding of embryo selectins to glyco-components on uterus epithelial cells
4- Integrins, laminin and fibronectin are involved in initial penetration

Question 16

What three proteins are involved in initial penetration of the embryo to the wall?

Answer 16

1- Integrins
2- Laminin
3- Fibronectin

Question 17

When does implantation of the blastocyst start?

Answer 17

6-7 days

Question 18

How does the blastocyst implant into the uterine wall?

Answer 18

1- Trophoblast becomes ‘invasive’
2- Syncytiotrophoblast and cytotrophoblast help penetrate uterus epithelium
3- Syncytiotrophoblast invade via metalloproteases

Question 19

On day eight, what two layers form in the embryo?

Answer 19

1- Epiblast

2- Hypoblast

Question 20

When does the amniotic cavity begin to form?

Answer 20

8 days post fertilisation

Question 21

Where does the amniotic cavity begin to form?

Answer 21

Within the epiblast

Question 22

On day eight, what do hypoblast cells begin to do?

Answer 22

They begin to flow or migrate outwards to coat the blastocyst cavity

Question 23

On day nine,where are hypoblasts found?

Answer 23

1- Coating the blastocyst cavity

2- Form primary yolk sac

Question 24

What happens on day nine?

Answer 24

1- Hypoblast cells coat blastocyst cavity, forming the primary yolk sac
2- Spaces develop within the syncytiotrophoblast to form trophoblastic lacunae
3- Amniotic cavity has formed within the epiblast
4- Extraembryonic mesoderm begins to form deep to the trophoblast

Question 25

What happens on days eleven and twelve?

Answer 25

1- Embryonic disc at bottom of amniotic cavity has two layers 2- Blastocyst burrows completely into endometrium 3- Primitive placental circulation is established by syncytiotrophoblasts eroding through the walls of large maternal capillaries leading to blood bleeding into the trophoblastic lacunae 4- Chorionic cavity forms

Question 26

How is primitive placental circulation established?

Answer 26

1- Syncytiotrophoblasts (SCT) 2- SCTs burrow through walls of large maternal capillaries 3- Leads to blood flowing into trophoblastic lacunae

Question 27

When can breakthrough bleeding happen?

Answer 27

When primitive placental circulation is established by SCTs

Question 28

What features are established by the end of the second week?

Answer 28

1- Two layers, the syncytiotrophoblast and cytotrophoblast form in the trophoblast 2- Epiblast/ectoderm and hypoblast/endoderm form in the inner cell mass 3- Amniotic and chorionic cavities form

Question 29

What is pre-eclampsia?

Answer 29

``` 1- Condition 20 weeks into pregnancy 2- Hypertension 3- Proteinuria 4- Due to poor cytotrophoblast invasion into the spiral arteries, which then keep their muscular walls 5- This leads to hypertension ```

Question 30

What is ectopic implantation?

Answer 30

Implantation of blastocyst outside uterus

Question 31

What is the most common site of ectopic implantation?

Answer 31

Ampulla

Question 32

What increases the risk of ectopics?

Answer 32

Inflammatory disease of pelvis

Question 33

What are the main causes of congenital malformations?

Answer 33

1- Genetic 2- Environmental (least common) 3- Multifactorial or unknown (most common)

Question 34

What are the possible environmental causes of congenital malformations?

Answer 34

1- Drugs or chemicals e.g. nicotine, alcohol, chemotherapy 2- Infectious agents e.g. rubella, toxoplasma 3- Ionizing radiation

Question 35

What is foetal alcohol syndrome?

Answer 35

1- Disorder spectrum 2- Non-hereditary mental retardation and neurological deficit 3- Due to ingestion of alcohol during pregnancy

Question 36

What consequences does the ingestion of alcohol during pregnancy have?

Answer 36

``` 1- Foetal alcohol syndrome 2- Mental retardation and neurological deficit 3- Cleft lip/palate 4- Small jaw 5- Wide-set eyes 6- Dental abnormalities 7- Digit abnormalities 8- Small head 9- Short stature 10- CNS damage ```

Question 37

What protects against alcohol damage in the first two weeks?

Answer 37

Stemness of cells

Question 38

What damage may be caused by ingestion of alcohol during the 3-6 week period?

Answer 38

1- Implantation failure 2- Neurological defects 3- Minor developmental defects in face related to damage on neural crest cells

Question 39

What damage may be caused by ingestion of alcohol during the 6-7 week period?

Answer 39

Defects in corpus callosum which is a major hemisphere connection