Embryonic Development Flashcards
Where does fertilization occur?
Ampulla of the uterine (fallopian) tube
How is genetic sex determined?
1- Oocyte carrying X chromosome
2- Sperm may carry X or Y chromosome
3- XX: female
4- XY: male
What processes occur during the first week of development?
Ovulation to implantation
1- Ovulation of haploid oocyte
2- Sperm penetrates oocyte wall
3- Fertilised oocyte implants on uterine wall
What is the acrosome reaction?
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
What types of RNA does the egg cytoplasm contain?
1- Mitochondrial DNA
2- Maternal mRNA
When does the first mitosis begin?
After fertilisation
When is cleavage initiated?
Within 36 hours of fertilisation
What is a morula?
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
Why must the zona pellucida disappear?
For implantation on uterine wall
Up to what stage are cells totipotent?
Blastocyst stage
What is a blastocyst?
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
Which cells are removed for genetic testing in the early embryo?
5-6 days trophectoderm
When does the embryo bind to the uterus wall?
5.5 to 6 days post fertilisation
What part of the embryo binds to the uterus wall?
Embryonic pole
How does the embryo bind to the uterus wall?
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
What three proteins are involved in initial penetration of the embryo to the wall?
1- Integrins
2- Laminin
3- Fibronectin
When does implantation of the blastocyst start?
6-7 days
How does the blastocyst implant into the uterine wall?
1- Trophoblast becomes ‘invasive’
2- Syncytiotrophoblast and cytotrophoblast help penetrate uterus epithelium
3- Syncytiotrophoblast invade via metalloproteases
On day eight, what two layers form in the embryo?
1- Epiblast
2- Hypoblast
When does the amniotic cavity begin to form?
8 days post fertilisation
Where does the amniotic cavity begin to form?
Within the epiblast
On day eight, what do hypoblast cells begin to do?
They begin to flow or migrate outwards to coat the blastocyst cavity
On day nine,where are hypoblasts found?
1- Coating the blastocyst cavity
2- Form primary yolk sac
What happens on day nine?
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
What happens on days eleven and twelve?
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
How is primitive placental circulation established?
1- Syncytiotrophoblasts (SCT)
2- SCTs burrow through walls of large maternal capillaries
3- Leads to blood flowing into trophoblastic lacunae
When can breakthrough bleeding happen?
When primitive placental circulation is established by SCTs
What features are established by the end of the second week?
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
What is pre-eclampsia?
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
What is ectopic implantation?
Implantation of blastocyst outside uterus
What is the most common site of ectopic implantation?
Ampulla
What increases the risk of ectopics?
Inflammatory disease of pelvis
What are the main causes of congenital malformations?
1- Genetic
2- Environmental (least common)
3- Multifactorial or unknown (most common)
What are the possible environmental causes of congenital malformations?
1- Drugs or chemicals e.g. nicotine, alcohol, chemotherapy
2- Infectious agents e.g. rubella, toxoplasma
3- Ionizing radiation
What is foetal alcohol syndrome?
1- Disorder spectrum
2- Non-hereditary mental retardation and neurological deficit
3- Due to ingestion of alcohol during pregnancy
What consequences does the ingestion of alcohol during pregnancy have?
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
What protects against alcohol damage in the first two weeks?
Stemness of cells
What damage may be caused by ingestion of alcohol during the 3-6 week period?
1- Implantation failure
2- Neurological defects
3- Minor developmental defects in face related to damage on neural crest cells
What damage may be caused by ingestion of alcohol during the 6-7 week period?
Defects in corpus callosum which is a major hemisphere connection
