Ear and Eye Development
- Develop from placodes (ectodermal thicking visible on the surface).
- Important for sensory organ formation.
- Otic placode visible from week 4, disappears from the surface by week 5.
- Otic placode forms components of the inner ear.
- Develops from an optic placode.
- Visible from the end of the 4th week.
- It forms a lens.
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Nervous System Development:
- Apparent after gastrulation, 19-21 days post fertilisation.
- The neural tissue forms the ectoderm.
- The neural plate will give rise to the brain (cephalic region)
- The neural tube gives rise to the spinal cord (caudal region).
NEURAL TUBE CLOSURE:
- Neural plate rolls up to form neural tube with a neural crest forming at the boundary with ectoderm.
- 23-26 days post fertilisation- Folding of neural ectoderm to form a tube.
- Failure to do so results in open neural tube disorders.
NEURAL CREST FORMATION:
- Cells at the tips of neural folds do not participate in neural tube formation.
- They remain between the dorsal surface of neural tube and ectoderm.
- Later they will migrate to other locations e.g. melanocytes of skin, bone, cartilage, connective tissue of face.
- 44 pairs total, added from cephalic to caudal end.
- Added alongside neural tube in pairs.
- Appear first around 19 days post fertilisation.
- New somite pair every 90 minutes.
- Produce muscle, vertebral and rib bones.
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- 4th week- External structures visible.
- They present as buds that protrude outwards.
- Patterning is important to specify proximal, distal, dorsal, ventral digits.
- Forelimb bud presents first, and the hindlimb bud follows.
- Outgrowth processes from limb buds make hands and feet distinguishable.
- Condensations of cartilage show precursors of digits.
- Week 8- Apoptosis between digits causes separation.
- Bone growth is occurring too.
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- 22-23 days post fertilisation, when neural tube is closing.
- Visible on the ventral surface (anterior).
- Continues through to week 8.
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- Grows via branching morphogenesis.
- Endoderm and mesoderm supply most of the alveoli.
- Ectoderm provides neural innervation.
- Mesoderm provides musculoskeletal support.
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- Grows via branching morphogenesis, starting from ureter.
- Grows in close proximity to genitals.
- Undergoes 3 stages of development:
- Pronephros day 18
- Mesenephros day 24
- Metanephros day 35
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GI System Development
- Week 2-3 -Initially arises from endoderm.
- After week 4, other germ layers contribute.
- Mesoderm = mesentary, smooth muscle, blood vessels.
- Ectoderm = enteric nervous system.
- Regions of the gut are divided into 3 cavities:
- Foregut = oral cavity, oesophagus, trachea, stomach.
- Midgut = small intestine and pancreas (herniated during development).
- Hindgut = colon
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