Embryology Flashcards
what is cleavage?
- one cell pinches, becomes two cells
what is the zona pellucida?
- shell of the egg
what is the polar body?
- shedding of unneeded genetic material
- 23 copies shed
what causes compaction?
- due to space constraint from zona pellucida
what is a blastomere?
- 2 cells
what is a morula?
- latin for mulberry
- 16 cell stage
what is an early blastocyst?
- formed by morula secreting fluid into itself
what is a blastocoel?
- hollow in the centre
- inner cell mass
- outer cell mass
define inner cell mass
- cellular mass
- hollow interior of round embryo
- forms the embryoblast
define outer cell mass
- outer edge of cellular mass
- forms trophoblast
define late blastocyst?
- trophoblast infiltrates the endometrium
- embryoblast and trophoblast present
define embryoblast
- gives rise to the embryo
define trophoblast
- gives rise to placental tissue
- provider of nourishment for embryo
week one detailed development
- 1 - sperm penetrate corona radiate, zona pellucida to reach the cyptoplasm where it injects its genetic material
- 2 - zygote is formed from male and female pronucleus
- 3 - after 30 hours - cells divide, 2 cell stage (cleavage). Now blastomere
- 4 - after 60 hours - 4 cell stage
- 5 - 8 cell stage
- 5 - day 3-4 - 16 cell stage (morula), inner cell mass & outer cell mass begin to form
- 6 - day 4-5 - 32 cell stage, early blastocyst. More compaction. Distinction form of blastocele
- 7 - day 5-6 late blastocyst. infiltration of epithelium
what is an ectopic pregnancy?
- when fertilised egg implants itself outside the womb, usually in the fallopian tubes
what % of ectopic pregnancies are tubal?
95%
what percentage of ectopic pregnancies are in the ampullary?
- 70%
what does an embryo blast give rise to?
- embryo
what does trophoblast give rise to?
- placental tissue
- provides nourishment for embryo
what happens to the location of the blastocyst at the end of week one?
- blastocyst has fully infiltrated the endometrial lining
- trophoblast mixes with maternal blood
what does the outer cells mass form in week one and then week two?
- trophoblast & cytoblast
- syncytiotrophoblast
what begins to form on day 7/8?
- early formation of bilaminar germ (embryonic disc)
- embryo blast turning into 2 distinct tissue types
what happens on day 9? (4)
- primitive yolk sac forms
- fibrin coagulum present - this will disappear as endometrium closes completely
- hypoblast becomes smaller
- epiblast becomes larger
what happens on day 12?
- trophoblastic lacunae meet maternal blood supply to form maternal sinusoids
- endoderm cells replace hypoblast
what happens on day 13? (4)
- primary villi present which give shape to placental tissues.
- trophoblastic lacunae present - spaces of syncytiotrophoblast filled with maternal blood supply -> give rise to placenta and blood supply to the embryo
- connecting stalk which gives rise to structures of the umbilical chord. amniotic cavity
- secondary yolk sac which was the ventral cavity
what happens in week 2 development? (3)
- trophoblast-> 2 layers (cytotrophoblast & syncytiotrophoblast)
- embryoblast-> 2 layers (epiblast & hypoblast)
- 2 cavities formed (amniotic and yolk sac)
what happens during gastrulation in week 3 of development?
- formation of 3 germ layers (trilaminar germ disc)
- formation of primitive streak on epiblast surface w/ primitive node at cephalic end
- primitive streak-> signals to epiblast cells to move ventrally, under epiblast
- hypoblast cells-> endoderm
- layer between epiblast and endoderm -> mesoderm
- remaining epiblast-> ectoderm
when does mesoderm formation occur?
- week 3
- when embryo is rapidly growing
what does mesoderm differentiation lead and contribute to?
- leads to cephalocaudal and lateral folding of the embryo
- contributes to location of parietal and visceral mesoderms
3 types of mesoderm?
- paraxial mesoderm
- intermediate mesoderm
- lateral plate mesoderm
cephalocaudal meaning?
- head to tail
what is neurulation?
- formation of neural tube
- notochord induces overlying ectodermal cells -> neuroectoderm
how does neurulation occur?
- notochord and neuroectoderm form
neuroectoderm froms neural plate - neural plate-> lateral neural folds and midline neural groove
- neural folds-> midline fusion, cervical region
what doe the neural tube become?
- brain and spinal cord
what day does the anterior (cranial neuropore) close?
- day 25
what day does the posterior neuropore close?
- day 28
what is spina bifida?
- neural tube fails to close correctly
what are the three types of spina bifida?
- spina bifida occulta
- meningocele
- meningomyelocele
- distinguishable by level of tissues effected
type determines treatments and management
what are natural crest cells?
- the ‘wandering’ germ layer/ cell group
- derived in process of neurulation, splitting off from neuroectoderm
- contribute to many structures, mostly head/ neck region
neural crest derivates
- head - face/skull connective tissue and bones, dermis of face and neck, smooth muscle in blood vessels
- neural components - schwann cells, glial cells, meninges, cranial nerve ganglia, spinal (dorsal root) ganglia, other autonomic ganglia
- glandular tissues - thyroid gland c-cells, adrenal medulla
- heart septum components
- melanocytes (of skin)
what are the three primary brain vesicles?
- prosencephalon
- mesencephalon
- rhombencephalon
5 secondary brain vesicles and their derivatives
- prosencephalon-> telecephalon and diencephalon
- mesencephalon remains the same
- rhombencephalon-> metencephalon and myelencephalon
where does lumbar puncture take place?
- subarachnoid space, without puncturing spinal chord
- between L4 and L5
peripheral nervous system origins
- neural crest
- neuroectoderm
