Embryology Flashcards
How long is the pre-natal period?
38 weeks (some say 40)
How many weeks is full term?
39 - 41 weeks
What week classes as post-mature period?
After 41 weeks
What week counts as premature?
Before 38 weeks
Describe the meiotic divisions of oocytes
Describe the meiotic divisions in spermatocytes
What are polar bodies and what do they do?
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
Where does fertilisation take place?
Ampulla (2ndary oocyte is also produced here)
What is the acrosomal reaction?
- Fusion: Outer membrane of the egg fuse with the sperm plasma membrane
- Release: the contents of the acrosome (head of the sperm) are released, including lytic acrosomal materials
- Digestion: Lytic acrosomal materials digest the oocyte’s glycoprotein coat
- Attachment: the bindin adheres to the inner acrosomal membrane, allowing sperm head to attach
What factors affect acrosomal reaction?
Progesterone
Calcium
Zona protein
Describe stages in 1st week of embryonic development
- Fertilisation occurs within the ampulla of the uterine tube
- cleavage
- morula
- blastocyst
- beginning of implantation
What are the results of fertilisation?
- Restores the diploid number of chromosomes (46)
- Determines sex
- Initiates cleavage
When do embryonic cells have pluripotency?
Stem-cell properties
Until the organs start to develop
Describe the stages (1-5) of cleavage and compaction
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
When does implantation occur?
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
- What are the types and frequency of twins
- What factors influence the chance
- Monozygotic (identical) - 10%
Dizygotic (non-identical) - 90% - Age (by 35 doubles chances)
IVF
Previous children
What is an ectopic pregnancy? Where is the most common site?
- Development of blastocyst outside of the uterus
- Most common site is the ampulla in uterine tube (80%) but can leave uterine tube through fimbriae and implant in abdominal wall (1.4%)
2nd week: continuation of implantation
What happens to the embryoblast on Day 8?
Differentiates into bilaminar disc
1. Epiblast layer
2. Hypoblast layer
3. Formation of amniotic cavity
Formation of extraembryonic structures
What happens on day 9-12 embryonic development?
- Fully implanted blastocyst
- penetration site forms plug (should be sealed by day 14 but sometimes blood can leak “implantation bleeding”)
- Lucunae fuse to form networks
What happens on day 14 of embryonic development?
Connecting stalk forms which becomes the umbilical cord
Summarise the 2nd week of embryonic development
- Complete implantation of blastocyst
- embryoblast develops into bilaminar disc: epiblast and hypoblast
- Maternal blood fills lacunae within trophoblast
- Cavities form: amniotic and yolk sac
- Formation of connecting stalk
Week 3: Gastrulation - trilaminar disc
- What is the source of cells for all 3 germ layers?
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 *
Week 3: gastrulation - trilaminar disc
What are the 3 germ layers found within the epiblast?
- Ectoderm
- Mesoderm
- Endoderm
What does the Ectoderm give rise to?
- Brain
- Spinal cord
- PNS
- Sensory epithelium of the ear, nose and eye
- Skin including nails and hair