Embryology Flashcards
Name for fertilised egg up to week 8?
Embryo
Name for fertilised egg from week 9 onwards?
Foetus
Name the 6 stages of embryogenesis?
Gametogenesis, fertilisation, cleavage, gastrulation, morphogenesis and organogenesis
When does cleavage start and what 2 things happens?
- Within 1-4 days
- Cells divide to form a morula then blastocyst
- Compaction occurs when cell junctions form and fluid supplies outer cells
Number of cells in a morula + blastocyst?
> 16 + > 100
Number of cell said to be totipotent in an embryo?
Up to 8
When does gastrulation occur and what happens?
Week 3 and germ layers form
Name the 3 germ layers?
Endoderm, mesoderm and ectoderm
What happens in morphogenesis + when does it occur?
Embryo folds from flat shape into a tube + week 4
What happens in organogensis?
Organs form
3 steps of sperm entering an egg?
- Sperm binds to zona pellucida
- Sperm releases acrosomal enzymes which allow sperm into egg and fusion
- Egg releases cortical granules to prevent more sperm binding
Where does a blastocyst normally implant and what happens straight after implantation?
Upper dorsal uterus and hatching (sheds zona pellucida)
Name the outer layer of a blastocyst and its 2 sublayers?
Trophoblast and cytotrophoblast + synctiotrophoblast
Which blastocyst layer is the outermost and attaches to the uterine wall?
Synctiotrophoblast
Name the inner layers + associated surfaces of a blastocyst?
Epiblast (dorsal) and hypoblast (ventral)
What forms the amniotic cavity?
The epiblast
What forms the yolk sac + definitive yolk sac?
The hypoblast
What is the main cavity that surrounds the yolk sac + amniotic cavity and what does it grow inside?
The chorionic cavity + extraembryonic mesoderm
By what day is implantation complete?
9
By what day does the definitive yolk sac start to form?
13
Layer that the chorionic cavity forms under the cytotrophoblast?
Extraembryonic mesoderm
2 structures that form on the epiblast by week 2 + function?
Oropharyngeal membrane (forms mouth) + primitive streak (needed for gastrulation/germ layer formation)
How do the germ layers arise?
- Cells move down via primitive streak
- Replace hypoblast with endoderm
- Replace epiblast with ectoderm
- Mesoderm is the middle layer
Ectoderm becomes the?
Skin + nervous system
Mesoderm becomes the?
Tissues e.g. bone, muscle
Endodoerm becomes the?
Lining of the GI, resp and urinary tract
Lateral folding forms what 2 things?
Thoracic and abdominal cavity
Cranial folding does what 2 things?
Forms the foregut + moves heart tube into thoracic cavity
Caudal folding forms what 3 things?
Hindgut, anus and umbilical cord
What is epigenetic control?
Preferential expression of either the maternal or paternal copy of a gene
Type of junction that form during compaction + function?
Gap junctions + allows fluid to reach outer cells in the morula/blastocyst
Order of 3 folding movements?
Lateral, cranial and caudal
What week during development has the highest risk of inducing a birth defect?
Week 5
What organ is the most common to be affected by birth defects?
The heart
What makes up the Tetralogy of Fallot + associated condition?
Pulmonary stenosis, right ventricular hypertrophy, overriding aorta and VSD + DiGeorge syndrome
