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
What does the Mesoderm give rise to?
- Bone
- Cartilage
- Blood cells
- Blood vessels
- Muscle
- Heart
- Kidneys
What does the Endoderm give rise to?
- Respiratory tract
- Digestive tract
- Liver
- Pancreas
- Urinary bladder
What direction does development occur in?
Cephalocaudal direction (head to toe)
What happens in the 3rd and 4th week of development?
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
What foldings occur in the 3rd and 4th weeks?
- Lateral
- Cephalocaudal
Summarise week 3-8 of embryonic development
- Gastrulation: establishment of ectoderm, mesoderm and endoderm layers
- Neurulation: formation of the neural tube
- Foldings: craniocaudal and lateral
- Organogenesis: major organs have begun being formed
What are the main events during the fetal period? (week 8-38)
- Maturation of tissues and organs
- Rapid growth of fetus
- Growth in length (month 3-5)
- Growth in weight (last 2 months)
In weeks define the embryonic and fetal period
- Embryonic: 3-8 weeks
- Fetal: 8-38
When is the highest risk of birth defecs being induced?
5 weeks
Define: embryo
The pre-fetal period of fertilisation until 8th week of development
Define: Blastula
Early embryonic form produced by cleavage of zygote and consists of spherical layer of cells surrounding fluid-filled cavity
Define: Fertilisation
Process by which 2 gametes (reproductive cells with single haploid set of chromos) fuse to form a zygote
Define: differentiation
Process where unspecialised cells/tissues are systemically modified/altered to achieve specific pysical forms, physiological functions and chemical properties
Define: Germ layer
Primary layers of cells of the embryo from which the tissues and organs develop
Gastrulation = process of forming 3 germ layers
