Embryology Flashcards
What is the embryonic period?
Week 3-8
What are the 3 germ layers and in what process do they appear?
Endoderm
Mesoderm
Ectoderm
Formed in gastrulation
When does gastrulation occur?
Third week of development- the start of the embryonic period
Why is week 2 the week of twos?
Trophoblast splits into two layers- cytotrophoblast and the syncytiotrophblast
Embryoblast gives rise to to cell layers-Bilaminar disc- epiblast and hypoblast
Hypoblast gives rise to two cavities - amniotic and primary yolk
List the germ layers and their derivatives
Endoderm- hypoblast
Mesoderm- epiblast
Ectoderm- epiblast
Outline the mesoderm organisation
The mesoderm sits between the ecto and end term apart from in one small area at each end of the body.
Which two future areas lack mesoderm?
Anus and mouth
What does ectodermal tissue give rise to?
Organs and structures that contact the outside world
- epidermis
- nervous tissue
Muscle, cartilage, bone and the CVS system are all formed from which germ layer?
Mesoderm
On day 16 what feature appears?
Primative streak and primative node appear on the dorsal surface of the epiblast at causdal end
How is a third layer formed from the bilaminar disc?
Epiblast cells migrate to the primitive streak and invaginate epiblast to displace the hypoblast- the new middle layer is the mesoderm. The epiblast is the ectoderm and the hypoblast is now called endoderm
How does gastrulation give left to right asymmetry?
The primitive node gives signalling molecules off that are moved more to the left by ciliated cells. This means that to the left of the notochord left sided signals are send and to the right side signals for right sidedness are sent.
List some anatomical left/right assymetry.
Liver on right
Stomach and spleen on left
Right lung 3 lobes left 2
Where does the primitive streak form?
caudal epiblast
What does gastrulation achieve?
3 germ layers
precursor tissue in correct place for subsequent morphogenesis.
What determines the fate of invaginating epiblast cells in gastrulation?
Position of invagination on the streak
What is the notochord?
Solid rod of cells running in the midline that has a signalling role.
What happens to the ectoderm that overlies the notochord?
Differentiates to neuro-ectoderm
Describe neural tube formation.
Ectoderm over notochord thickend and forms a slipper shaped neural plate.
The edges lift and curl toward each other, joining to make the neural tube.
Describe neuralation.
Ectoderm over notochord thickend and forms a slipper shaped neural plate.
The edges lift and curl toward each other, joining to make the neural tube.
Splancnic mesoderm sits adjacent to which other germ layer?
Endoderm
Where is the paraxial mesoderm found and what does it form?
Found adjacent to the notochord.
It segments into somites in a cranio-caudal sequence.
How many somites are lost?
42-44 present at end of week 5
Final count is 31
11-13 lost
What do somites give rise to?
Musculo-skeletal system
Dermis
How do somites become sclerotomes and dermomyotomes?
Ventral wall of somite degenerates. Some free cells become sclerotome and the dorsal surface from a bilayer of dermatome and myotome.
What happens to the dermmyotomes?
They migrate with proliferation of the mesoderm
What does sclerotome form?
Bones
Dermatome gives rise to what tissue?
Dermis
Muscles are derived from what part of a dermamyotome?
Myotome
What repeating structures form because of mesodermal somite formation?
Vertebrae
Ribs
Intercostal muscles
Spinal cord segments
How many spinal nerve pairs do we have?
31- from 31 somites
What is the term given to the future mouth in embryology?
Buccopharyngeal memebrane
In early embryogenesis where does the cariogenic field sit relative to the buccopharyngeal membrane?
Above it- more cranially
Name the two types of folding seen in the embryo.
Cephalocaudal folding
Lateral folding
What does folding achieve?
Creates a ventral body
Pulls amniotic membrane around the disk
Connecting stalk pulled ventrally
What is there at the end of week 4?
Start of nervous system
Segmentation of the body so specific sites have specific cells for specific functions
Embryo has folded so all precursor tissues are in the correct place
Why is embryogenesis important in medicine?
Understanding of congenital diseases and teratogens
Understanding embryogenesis helps treat diseases
Embryonic stem cell work
In the cervix what is the Os?
The openings of which there is an internal and an external
Where does fertilisation take place?
the ampulla
Which is bigger a spermatazoa or an ovum?
ovum
Within how many days before ovulation must sperm be introduced to fertilise an egg?
Within 5 days
How long is the secondary oocyte viable for?
12-24 hours
What is capacitation of sperm and why is it important?
Tail of the sperm moves faster which alters its plasma membrane and allows fertilisation
What layers surround the secondary oocyte from the outside in?
Corona radiata
Zonapeulicida
Perivitelline space
Membrane
What happens when the female and male pronucleus join?
Mitotic disivion. No single cell uni nuclear stage
What helps the female not to reject the embryo initially?
Sperm and seminal fluid help reshape immunity
What is embryonic age?
Time since fertilisation
How is gestational age different to embryonic age?
Embryonic age +2 weeks
Time since last menstruation not fertilisation
What is the germinal stage?
up to end of 2nd week
What is the germinal stage?
up to end of 2nd week embryonic age
What is the foetal period?
week 9-38 of the embryonic age
On Day 3 after fertilisation what does the embryo resemble and whats it called?
Mulberry
Morula
Describe the structure of an epiblast.
Outer cell mass encases
- Inner cell mass
- Blastocyst cavity
What day is implantation?
day 6
What implants into the womb wall?
Synciotrophoblast
Describe the structure of an epiblast and what stage this forms?
Outer cell mass encases
-Inner cell mass
-Blastocyst cavity
day 4
Which cells line the outer edge of the primitive yolk sac and connect to the trophoblast?
Amnioblast cells
What sit between the primary yolk sac and the trophoblast?
Exocoelomic membrane?
What is the outer cell mass called in the blastocyst?
trophoblast
Which cells line the outer edge of the primitive yolk sac and connect to the trophoblast?
The epiblast encases the amniotic cavity
What sit between the primary yolk sac and the trophoblast?
The hypoblast lines the primary yolk sac
What is the function of the zone pellucida?
prevents blastocyst/ morula implanting in oviduct
What is the function of the zone pellucida?
prevents blastocyst/ morula implanting in oviduct and would stop the morula getting bigger.
How long is histiotrophic nutrition vital for and where does it come from?
Trophoblast provides nutrition upto 12th week in humans
How long is histiotrophic nutrition vital for and where does it come from?
Trophoblast provides nutrition up to 12th week in humans
What term describes maternal blood providing foetal nutrition?
haemotrophic nutrition
Where in the womb should implantation happen?
Upper part of the uterine wall
More commonly posteriorly.
What is the term used for a pregnancy that implants on the wrong gynaecological structure?
Ectopic pregnancy
What is placenta previa?
Impantation over the cervix- risk of massive haemorrhage at delivery
What lines the chorionic cavity?
Extra embryonic somatic mesoderm
