Early Embrology Flashcards
Pre embryonic period
First 2 weeks of life
Morphogenesis
Development of form and structure
Differentiation
Cells specalise to carry out a function
Gestation period
38 weeks
Cleavage
When cells divide without growing in size
Zygote
Fertilised oocyte/ovum
Ovaries
Make / store eggs/oocytes and produce hormones that control pregnancy
Fallopian tubes
Connect ovaries to uterus
Zona pellucida
Glycoprotein coat that surrounds the oocyte/egg
Morula
When there’s 8 cells within the zona pellucida
Cells in morula are totipotent
Have the capacity to become any type
At what stage is the zygote allowed to reach before it is implanted in IVF?
Zygote allowed to reach morula stage and is then implanted into mother, the cells are still totipobent
Zygote travels through fallopian tube to junction with uterus in the first
4 days
Emryoblasts Clump and differentiation happens (week l)
Trophoblasts on the outside and embryoblasts in middle
Compaction (Week 1)
Embryoblasts clump together leaving a cavity called the blastocoel
Trophoblasts line outside of blastocyst
They are gonna be needed for support
Potency after compaction
Now pluripotent
After compaction Zonapellucida breaks down
Means Blastocyst can interact with the uterine tissue
When does Implantation begin?
Week 1
What 2 things happen together after implantation?
Placenta and embryo form, in early stages placenta = priority
Why is Week 2 is the week of 2’s?
2 cell layers emerge:
Outer Cell Mass:
Syncytitotrophoblast (Multinucleated sheett of trophoblasts good for support and transport)
Cytotrophoblasts
Inner Cell Mass:
-Epiblast
-Hypoblast
What does the Bilaminar Disc consist of?
Epiblast
Hypoblast
What is the Amniotic cavity?
Cavity that forms between cytotrophoblasts and epiblasts
Ectopic Pregnancy
When Implantation of the blastocyst occurs elsewhere other than the normal locations
Placenta Previa
When implantation happens in the lower uterine segment. So placenta grows low down and can block cervix
Embryonic Period
Weeks 3 -8 Where all major structures and systems are formed
Ectoderm Derivatives
Epidermis (Skin)
CNS
Mesoderm Derivatives
CVS (Cardiovascular System)
MSK (Muscular Skeletal)
Fetal period
Week 9-38
When is the:
Pre embryonic period
Embryonic period
Fetal period
Fertilisation-week2
Week 3-week 8
Week 9-week 38
Endoderm derivatives
Lining of the gastrointestinal system (gi), lining of respiratory system, parenchyma cells (functional cells) of glands
Pre embryonic period steps
Blastulation
Zone pellucida breaks down (implantation can now begin)
Cell differentiation of trophoblasts and embryoblasts
Amniotic cavity forms, gap between trophoblasts and epiblasts
Blastulation (formation of the blastocyst) starts when cleavage stops
Zygote travels though fallopian tubes, cleavage of internal cells( blastomeres) once 32 blastomeres reached it’s called a morula. Blastomere’s differentiate outer layer = Trophoblasts. Inner cell mass = embryoblasts, compaction, embryoblasts compact leaving a cavity could a blastocoel, structure is now called a blastocyst blastulation has happened.
Gastrulation (starts when primitive streak forms)
The formation of the trilaminar disc / the 3 germ layers
Embryoblasts differentiate
Forms bilaminar disc
Epiblasts at top layer
Hypoblasts bottom layer
Bilaminar disc =
Epiblasts
Hypoblasts
Trophoblasts differentiate
Very top of blastocyst syncytiotrophoblasts
The rest are cytotrophoblasts
Syncytiotrophoblasts role
Adhere to and invade endometrium cells, enable utero-placental circulation allows blastocyst to get nutrients from mother
Cytotrophoblasts
Help form connection with mother
Hypoblast function
Forms/lines the primary yolk sac
How does the Secondary yolk sac form?
Pinches off of primary yolk sac
Embryonic period
All major structures and systems are formed
weeks 3-8
Primitive streak
When epiblast cells migrate to centre and invaginate/dive downwards displacing the hypoblasts creating a further 2 layers
The 3 germ layers called trilaminar disc
How does the notochord form in the mesoderm?
Epiblast cells dive down from the primitive node into the mesoderm
Notochord drives neuralation.
Found under where primitive streak formed
Notochord
Sends signals to ectoderm causing differentiation to neuroectodermn forming neural plate/groove
Neural plate curls inwards and out of plane forming neural tube
Neural crest cells break off from ectoderm (will later differentiate oo form the peripheral nervous system
Neural tube role
Will form the Central nervous system
Sends signals to the mesoderm causing it to differentiate
What does the Mesoderm differentiate into? Remember PISS
Paraxial mesoderm (forms somites)
Intermediate mesoderm (forms kidneys)
Somatic mesoderm (dicephragm and limb muscles)
Splachnic mesoderm ( muscles of heart and other internal organs)
Intra embryonic coelom (spaces in body)
What are somites?
What are the 3 somite derivatives?
Somites are segmented paraxial mesoderm
Dermatome
Myotome
Scleratome
Dermatone
Gives rise to skin
Myotome
Gives rise to area of skeletal muscle
Sclerotone
Gives rise to a vertebra and rib (bones)
How many somites?
31
What is situs inversus?
Complete mirror image of organ locations in chest and abdomen are a mirror image of what the normal human anatomy should be
How does situs inversus usually occur?
As a result of immobile cilia at the primitive node
