Embryo Development Flashcards
Pronucleus
Either of a pair of gametic nuclei, in the stage following meiosis but before their fusion leads to the formation of the nucleus of the zygote.
Polar body
The cell that results from the asymmetric division of an oocyte
Morula compaction
- Occurs at around 16- to 32- cell stage
- Tight junctions form between outer cells
- Individual cells become less distinct (cell merge into “amorphous mass”)
- Sodium pumped into interior creates osmotic gradient -causes water to enter the embryo
Blastocyst Cell Populations
- Inner cell mass cells
- Trophpblast cells
- Inner cell mass cells give rise to embryo proper
- Trophpblast cells give rise to chorion and amnion (extraembryonic membranes). These cells provide signal for maternal recognition of pregnancy
Role of the zone Pellucida
- Keeps blastomeres together during early cleavage stages
- Prevents multiple embryos from sticking together and forming chimeric conceptus
- Protects embryo
- Maintenance of spherical shape of blastocyst
Describe the “hatching” of a blastocyst
- Blastocyst increases in diameter
- Enzymes produced by trophoblast weaken zona pellucida
- Blastocyst exerts pressure ‘pulses’ by collapsing and re-expanding
- Zona splits at weakest point and embryo completely sheds zona as split widens
Embryonic Diapause
- Reproductive strategy that delays implantation
- Embryo remains in state of suspended animation at blastocyst stage (minimal or no cell division)
- Results in extended gestation
What are the 2 types of embryonic diapause?
- Faculative diapause
- lactational delayed implantation
- rodents, marsupials - Obligate diapause
- seasonal delayed diapause
- roe deer, bats
Embryonic nutritional support - preimplantation
- Organic molecules and ions by transport mechanisms from oviducal and uterine secretions
- O2 and CO2 by diffusion
Embryonic nutritional support - attachment
- Exchange between trophoblast and epithelial cells
- Invasive (primates rabbits, dogs, cats, rodents)
- Non-invasive (pigs, mares, ewes, cows)
Embryonic nutritional support - implantation
- Exchange between fetal vasculature and maternal blood
Control of preimplantation development - Initial blastomere divisions
Maternally derived mRNA transcripts and proteins accumulated during oocyte maturation
Control of preimplantation development - After embryonic activation
- Embryonically derived mRNA transcripts
- Newly synthesised proteins
- Autocrine growth factors (embryonic)
- Paracrine growth factors (maternal)
What are epigenetics?
- Heritable genetic modifications that are not due to changes in the DNA sequence
- Cause paternal and maternal genes to be differentially expressed
Twinning
- Monozygotic: identical, derived from the same embryp
- Dizygotic: fraternal, two oocytes fertilised separately by two sperm
