Prenatal Development Flashcards
Embryo vs fetus
- Embryo: organ systems developing (first 8 weeks)
- Fetus: anything after that
Describe gastrulation (from implantation onwards)
- After implantation, inner cell mass differentiates into epiblast and hypoblast
- Hypoblast eventually becomes yolk sac (which nourishes the fetus before the placenta takes over + produces blood cells)
- Epiblast eventually becomes amnion
- Primitive streak forms on the epiblast at the caudal end, and epiblast cells fold inwards ventrally
- First layer of cells displace hypoblast, and become endoderm
- Second layer become mesoderm
- Third layer remain, and are ectoderm
Describe neurulation
- After gastrulation, a cord of mesoderm forms the notochord
- This prompts the ventral invagination of ectoderm, like an invisible finger pulling it inward
- Ectoderm folds in on itself, leaving behind neural crest cells at the pinch points
- Neural tube goes on to form CNS, and crest cells for PNS
What are 3 possible defects that can arise if the neural tube doesn’t close properly?
- Anacephaly (cranial neural tube doesn’t fold; IWL)
- Encephalocele (brain bulges outward)
- Spinal dysraphism (spinal cord/vertebral malformation). Leads to spina bifida (what are the types?)
- Exencaphly (brain outside skull/no skull at all)
Describe mesoderm areas from medial to lateral
- Lateral to the notochord (in order) arises the paraxial, intermediate, and lateral mesoderm
- Paraxial forms dermatomes (skin/meninges), myotomes (trunk/back/limb sk muscles) and sclerotomes (vertebrae, IVDs, and ribs)
- Intermediate forms kidneys and gonads
- Lateral forms adrenals, lymph nodes, GIT muscle (splanchnic) and sternum/limb buds (somatic)
How many days after conception is the neural groove present? How does this relate to miscarriage (memory tick)
- 20 days after conception
- 20 weeks post conception is miscarriage; similarity represents that brain is key to life
How many days for the fetal brain to split into its 4 major components? What are they called?
- 22 days (2 days after neural tube; split = 2)
- Areas are telencephalon, diencephalon, mesencephalon, rhombencephalon (rhombus shaped)
What happens to neural cells as they migrate away from the neural tube during fetal development?
They differentiate, and gain the ability to produce neurotransmitters.
Once neural tube cells proliferate, they are ready to migrate to form structures of the nervous system. What are two ways by which they can do this?
- Radial (neurons are guided by radial glia outward, perpendicular to the ventricular surface)
- Tangential (neurons are guided out by chemoattractants, parallel to the ventricular surface)
Synaptogenesis depends on the presence of which glial cell?
- Astrocytes
- Smart = space cells = spaceX = musk
What % of neurons die after migration? What mediates this?
- 40-75% of neurons die (!!!)
- Neurons compete for growth factors and neurotophins (break this down to root words). Those that fail are pruned
What are the 3 key stages of fetal brain development?
- Proliferation/migration (incl. cortical folding)
- Neuronal maturation (incl axons/synaptogenesis)
- Myelination
Summarise events of fetal brain development
- Splitting into four parts on day ???
- Proliferation of neural tube cells
- Migration to site of function (by which 2 mechs?)
- Axonal growth/neuronal matuation
- Synpatic pruning c
- Myelination
What tissues arise from neural crest cells?
- Adrenal cortex chromaffin cells
- Sensory neurons
- Neurons and glia of cranial nerve ganglia
Describe the role of radial glia, incl. asym division
- Radial glia divide asymmetrically, producing more radial glia and neurons
- They radiate outwards from from the central canal to the outer aspect, forming tracks for neurons to migrate along
True or false: other than more radial glia and neurons, radial glia also give rise to other macroglia
- True
- This can include astrocytes, oligodendrocytes and ependymal cells
Where do radial glia end up? Why is this cool?
- They end up as ependymal cells
- This is cool because, eventually, we can use them to allow regeneration of nerve cells
Recount from neurulation through to dorsal/ventral horn formation and spinal canal formation. What proteins influence cell differentiation?
- Neural tube folds, then cells begin to differentiate
- As dorsoventral axis is squished, neural tube is pinched centrally, creating the “wings of the butterfly”
- Proteins affecting cell migration/differentiation include sonic hedgehog protein (ventral) and bone morphogenic protein/BMP (dorsal)
How do we diagnose neural tube defects?
Ultrasound
Recall the timeframes (wks) of the five stages of fetal lung development
- 4-7
- 5-17
- 16-26
- 26-36
- 36-full term
Recall the names of the five stages of fetal lung development
- Embryonic
- Psuedoglandualr
- Canalicular
- Saccular
- Aveolar
(EPCSA -> except me. because that’s gross)
What are the structural features that exist at each stage of fetal lung development?
- Embryonic: two lung buds
- Psuedoglandular: Airway branching, SMCs and mucous glands
- Canalicular: last stage of branching morphogenesis. Distal airways begin to widen. Capillaries begin to connect to them
- Saccular: saccules increase in size, and are wrapped in capillaries. Type 2 alveolar cells begin to appear (function?)
- Alveolar: Saccules are subdivided into alveoli
Names/functions of the three shunts in fetal circulation
- Ductus venosus: oxygenated blood from placenta is shunted into the IVC, bypassing liver
- Ductus arteriosus: allows blood to bypass the lungs (from pulmonary artery to aorta)
- Foramen ovale: oxygenated blood from the right heart (where has it come from?) shunted from right to left atrium, since it’s ready to be sent round the body
Describe fetal heart development
- Myocardial progenitors (from the mesoderm) begin to migrate to form the cardiac crescent
- Heart tube forms, and begins to beat around day 22 after conception (same day as brain _____)
- Myocardial progenitors differentiate into cardiomyocytes, endothelial cells, and conductive neural tissue. Looping and folding produces heart chambers
- Ectoderm cells migrate to the heart, and produce SMCs as well as neurons
