Embryology

Question 1

How long is the pre-natal period?

Answer 1

38 weeks (some say 40)

Question 2

How many weeks is full term?

Answer 2

39 - 41 weeks

Question 2

What week classes as post-mature period?

Answer 2

After 41 weeks

Question 3

What week counts as premature?

Answer 3

Before 38 weeks

Question 4

Describe the meiotic divisions of oocytes

Question 5

Describe the meiotic divisions in spermatocytes

Question 6

What are polar bodies and what do they do?

Answer 6

Produced as a consequence of 1st and 2nd meiotic division. They ensure the cytoplasm and cellular machinery goes to the strongest of the oocytes to give rise to healthy mature oocytes.

They will disintegrate

Question 7

Where does fertilisation take place?

Answer 7

Ampulla (2ndary oocyte is also produced here)

Question 8

What is the acrosomal reaction?

Answer 8

1. Fusion: Outer membrane of the egg fuse with the sperm plasma membrane
2. Release: the contents of the acrosome (head of the sperm) are released, including lytic acrosomal materials
3. Digestion: Lytic acrosomal materials digest the oocyte’s glycoprotein coat
4. Attachment: the bindin adheres to the inner acrosomal membrane, allowing sperm head to attach

Question 9

What factors affect acrosomal reaction?

Answer 9

Progesterone
Calcium
Zona protein

Question 10

Describe stages in 1st week of embryonic development

Answer 10

1. Fertilisation occurs within the ampulla of the uterine tube
2. cleavage
3. morula
4. blastocyst
5. beginning of implantation

Question 11

What are the results of fertilisation?

Answer 11

1. Restores the diploid number of chromosomes (46)
2. Determines sex
3. Initiates cleavage

Question 12

When do embryonic cells have pluripotency?

Stem-cell properties

Answer 12

Until the organs start to develop

Question 13

Describe the stages (1-5) of cleavage and compaction

Answer 13

Day 0: 1 cell stage - zygote divdes by mitosis
Day 1: 2 cell stage - polar bodies, zona pellucisa and blastomere is present
Day 2: 4 cell stage
Day 3: 8 cell stage
Day 4: Morula is formed (16 cell stage) So here cells become compacted
Day 5: Blastocyst, due to polarisation beginning in the cell.
* The inner cell mass will develop into embryo
* Trophoblast will develop into the placenta
* Cavity forms because the zona pellucida starts to fill it with fluid

Question 14

When does implantation occur?

Answer 14

Day 6:
* Implants on the posterior or anterior wall of uterus
* Blastocyst attaches itself to the endometrial epithelium
* Zona pellucida disintegrates

Day 7:
* Invasion of the endometrial connective tissue
* Trophoblast becomes placents

Question 15

1. What are the types and frequency of twins
2. What factors influence the chance

Answer 15

1. Monozygotic (identical) - 10%
   Dizygotic (non-identical) - 90%
2. Age (by 35 doubles chances)
   IVF
   Previous children

Question 16

What is an ectopic pregnancy? Where is the most common site?

Answer 16

1. Development of blastocyst outside of the uterus
2. Most common site is the ampulla in uterine tube (80%) but can leave uterine tube through fimbriae and implant in abdominal wall (1.4%)

Question 17

2nd week: continuation of implantation

What happens to the embryoblast on Day 8?

Answer 17

Differentiates into bilaminar disc
1. Epiblast layer
2. Hypoblast layer
3. Formation of amniotic cavity

Question 18

Formation of extraembryonic structures

What happens on day 9-12 embryonic development?

Answer 18

1. Fully implanted blastocyst
2. penetration site forms plug (should be sealed by day 14 but sometimes blood can leak “implantation bleeding”)
3. Lucunae fuse to form networks

Question 19

What happens on day 14 of embryonic development?

Answer 19

Connecting stalk forms which becomes the umbilical cord

Question 20

Summarise the 2nd week of embryonic development

Answer 20

1. Complete implantation of blastocyst
2. embryoblast develops into bilaminar disc: epiblast and hypoblast
3. Maternal blood fills lacunae within trophoblast
4. Cavities form: amniotic and yolk sac
5. Formation of connecting stalk

Question 21

Week 3: Gastrulation - trilaminar disc

1. What is the source of cells for all 3 germ layers?

Answer 21

Epiblast at the primitive streak (a narrow groove with bulging regions on either side and elevated area around a pit)

*Epiblast cells invade the primitive streak and is the source of cells for all 3 germ layers *

Question 22

Week 3: gastrulation - trilaminar disc

What are the 3 germ layers found within the epiblast?

Answer 22

1. Ectoderm
2. Mesoderm
3. Endoderm

Question 23

What does the Ectoderm give rise to?

Answer 23

1. Brain
2. Spinal cord
3. PNS
4. Sensory epithelium of the ear, nose and eye
5. Skin including nails and hair

Question 24

What does the Mesoderm give rise to?

Answer 24

1. Bone 2. Cartilage 3. Blood cells 4. Blood vessels 5. Muscle 6. Heart 7. Kidneys

Question 25

What does the Endoderm give rise to?

Answer 25

1. Respiratory tract 2. Digestive tract 3. Liver 4. Pancreas 5. Urinary bladder

Question 26

What direction does development occur in?

Answer 26

Cephalocaudal direction (head to toe)

Question 27

What happens in the 3rd and 4th week of development?

Answer 27

Neurulation is where the neural plate forms the neural tube (brain and spinal cord) which will be complete by the end of the 4th week

Question 28

What foldings occur in the 3rd and 4th weeks?

Answer 28

1. Lateral 2. Cephalocaudal

Question 29

Summarise week 3-8 of embryonic development

Answer 29

1. **Gastrulation**: establishment of ectoderm, mesoderm and endoderm layers 2. **Neurulation**: formation of the neural tube 3. **Foldings**: craniocaudal and lateral 4. **Organogenesis**: major organs have begun being formed

Question 30

What are the main events during the fetal period? (week 8-38)

Answer 30

1. Maturation of tissues and organs 2. Rapid growth of fetus 3. Growth in length (month 3-5) 4. Growth in weight (last 2 months)

Question 31

In weeks define the embryonic and fetal period

Answer 31

1. Embryonic: 3-8 weeks 2. Fetal: 8-38

Question 32

When is the highest risk of birth defecs being induced?

Answer 32

5 weeks

Question 33

Define: embryo

Answer 33

The pre-fetal period of fertilisation until 8th week of development

Question 34

Define: Blastula

Answer 34

Early embryonic form produced by cleavage of zygote and consists of spherical layer of cells surrounding fluid-filled cavity

Question 35

Define: Fertilisation

Answer 35

Process by which 2 gametes (reproductive cells with single haploid set of chromos) fuse to form a zygote

Question 36

Define: differentiation

Answer 36

Process where unspecialised cells/tissues are systemically modified/altered to achieve specific pysical forms, physiological functions and chemical properties

Question 37

Define: Germ layer

Answer 37

Primary layers of cells of the embryo from which the tissues and organs develop *Gastrulation = process of forming 3 germ layers*