Embryology Flashcards
What is embryology?
The study of progression from a single cell to a baby in 9 months
What is special about zebra fish?
Translucent eggs that are outside the mother
Sequenced genome
Study birth defects
Where does fertilisation take place?
Ampullary region of the fallopian tube
How long is a sperm viable for?
5 days
How long is a secondary oocyte viable for?
12-24 hours
Why aren’t sperm rejected as they are foreign bodies?
Antibodies only form if the sperm gets in contact with the blood
Tight junctions stop sperm passing into blood
When is the germinal stage?
Fertilisation to the end of the second week
When is the embryonic period?
Beginning of third week till the end of the eighth week
When is the Foetal period?
Beginning of ninth week to birth (38 weeks)
What is the Zona Pellicuda?
Stops the blastocyte from adhering to oviduct
The loss of it is called hatching
What does trophoblast mean?
Food bud- becomes the yolk sac and placenta
What is Histiotrophic nutrition?
Nutrition provided to the embryo not from the maternal blood
Before week 12
What is haemoptrophic nutrition?
Nutrition provided by the mothers blood
After week 12
What is the implantation site?
Site of formation the placenta
Usually upper part of the body of the uterus in the posterior wall
What is an ectopic pregnany?
Fetus develops outside the Uterus
What is placenta previa?
Placenta blocks the neck of the uterus so interferes with delivery
What is Syncytium?
Together cells
What is syncytiotrophoblast?
Cells that merge together in the trophoblast
What is Cytotrophoblast?
Cells in the trophoblast
What happens in the second week of development?
Trophoblast differentiates into 2 layers
Embryoblast forms 2 layers- epiblast and hypoblast
Hypoblast forms the yolk sac and chorionic cavity
What happens during the embryonic period?
All major systems and structures are formed
When is the greatest risk of major congenital malformations?
Embryonic period
What are the key events and processes in early development?
Fertilisation and implantation Gastrulation Neurulation Segmentation Folding
Where do new features appear in the third week?
Dorsal surface of the epiblast
What is an ectoderm?
Organs and structures that maintain contact with outside world
What is a mesoderm?
Supporting tissues
What is an endoderm?
Internal structures
What is Situs inversus?
Complete mirror image viscera
Commonly results from immotile cilia
No associated morbidity
Problem arise if normal and mirror image disposition
What are the clear right and left body differences?
Liver on the right
Stomach and spleen on the left
Left lung has 2 lobes
Right lung has 3 lobes
When is Gastrulation?
Third week
What is Gastrulation?
Bilaminar disks are converted into trilaminar disks
Three germ layers, ectoderm, mesoderm and endoderm
How does Gastrulation occur?
Primitive streak forms in caudal epiblast, leading to migration and invagination of epiblast cells
Why does Gastrulation occur?
To ensure the correct placement of precursor tissues to allow subsequent morphogenesis to take place
What does the ultimate fate of invaginating epiblasts depend on?
Where in the streak or node they invaginate
What is the notochord?
Solid rod of cells running in the midline with important signalling role
Directs conversion of overlying ectoderm to neurectoderm
What do norochord signals cause?
Ectoderm to thicken
What is somites?
Organisation of paraxial mesoderm into segments
When and where do the 1st pair of somites appear?
Day 20 in the occipital region
How many somites will there be in total?
31
What do somites appear as?
Regular block of mesoderm cells arranged around a small cavity
What is organised degeneration of somites?
Ventral wall of somite breaks down, leading to formation of the sclerotome
What forms the dermomyotome?
Organisation of the dorsal portions
What is dermatome?
Skin section
What is myotome?
Muscle section
What is sclerotome?
Hard tissue section e.g. bone
What does organisation of mesoderm into somites give rise to?
Repeating structures e.g. vertebrae, ribs, intercostal muscles, spinal cord segments
How many pairs of spinal nerves are there?
31
What does folding achieve?
Draws together the margins of the disk which creates a ventral body wall
pulling amniotic membrane around the disc
pulling connective stalk ventrally
What happens by the end of the fourth week?
The nervous system has started to form
segments have appeared, assigning specific tasks to specific cells, the embryo has folded, putting everything in the right place
