Embryology Lecture Flashcards
Where does fertilisation normally take place?
In the ampullary region of the fallopian tube
What is embryonic age?
The time since fertilisation
What is the germinal stage?
Time from fertilisation to end of second week
What is the embryonic period?
The time from third week to end of eighth week
What is the foetal period?
The time from ninth week to birth at 38 weeks
What is the gestational age?
Time since last menstruation. Embryonic age age - 2 weeks
By day 3 of development the cell has developed an outer and inner cell mass. What are they called?
Outer = trophoblast Inner = blastocyst
What does the primitive endoderm contain?
Yolk sac and gut endoderm
What does the trophoblast (outer cell layer) contain?
Yolk sac and placenta
What is the definition of trophoblast?
Food bud
From what week are the nutrients provided by the mother’s blood?
Week 12 onwards
Where is the normal implantation site for the blastocyst (inner cell layer)?
The upper part of the body of the uterus on the posterior wall
What is a placenta previa and why might the mother need a caesarian section?
A placenta previa = placenta blocking the cervical opening
There would be extreme haemorrhage if delivered normally
What week of development does the trophoblast differentiate into 2 layers? What are they called?
Week 2
Cytotrophoblast
Syncytiotrophoblast
What are the 2 layers of the bilaminar embryonic disk called?
Epiblast
Hypoblast
The hypoblast contributes to formation of 2 cavities - what are they?
Yolk sac
Chorionic cavity
At the end of the 2nd week the epiblast (1 of the 2 layers of bilaminar disc) is disk shaped. In week 3 a feature appears on the epiblast - what is it called?
Primitive streak
What is the bioethics of the primitive streak?
Appearance of the primitive streak is the appearance of a defined individual
The bilaminar disk becomes a trilaminar disk - what are the 3 layers of this?
Ectoderm
Mesoderm
Endoderm
What is the process of creation of the ectoderm, endoderm and mesoderm called?
Gastrulation
What does the ectoderm create?
Organs and structure in contact with outside world
What does the mesoderm create?
Supporting tissues eg muscle cartilage and the vascular system
What does the endoderm create?
Internal structures
When does gastrulation begin and what is it?
3rd week development - start of embryonic period (week 3-8)
Bilaminar disk converted to trilaminar disk - three germ layers (mesoderm, endoderm and ectoderm)
What runs down the midline attaching to the node at the top of the primitive streak?
The notochord
What does the notochord do?
Converts ectoderm to neurectoderm (beginning of CNS)
What is the conversion of ectoderm to neurectoderm called?
Neurulation
When do somites first appear?
At day 20
Somites derive into 3 tissue types - what are they?
Dermatome (dermis)
Myotome (muscles)
Sclerotome (bones)
What is the buccopharyngeal membrane?
Future mouth site
At what development stage does implantation usually occur?
Blastocyst
From which embryonic tissue are the 3 germ cell layers derived?
Epiblast
What is the cloacal membrane?
Future anus
What is an ectopic pregnancy?
When blastocyst is in the fallopian tube rather than uterus
