Human Development

Nervous System:

  • 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.

SOMITE DEVELOPMENT:

  • 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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  • Created by: Shelby
  • Created on: 28-12-14 17:54

Ear and Eye Development

Ear 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. 

Eye Development:

  • Develops from an optic placode. 
  • Visible from the end of the 4th week. 
  • It forms a lens. 
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Nervous System Development:

Nervous System:

  • 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.

SOMITE DEVELOPMENT:

  • 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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Limb Development

  • 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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Heart Development:

  • 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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Lung Development

  • Grows via branching morphogenesis.
  • Endoderm and mesoderm supply most of the alveoli. 
  • Ectoderm provides neural innervation. 
  • Mesoderm provides musculoskeletal support.
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Kidney Development

  • Grows via branching morphogenesis, starting from ureter.
  • Grows in close proximity to genitals.
  • Undergoes 3 stages of development:
  1. Pronephros day 18
  2. Mesenephros day 24
  3. Metanephros day 35
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GI System Development

  • Week 2-3 -Initially arises from endoderm.
  • After week 4, other germ layers contribute. 
  1. Mesoderm = mesentary, smooth muscle, blood vessels.
  2. Ectoderm = enteric nervous system.
  • Regions of the gut are divided into 3 cavities:
  1. Foregut = oral cavity, oesophagus, trachea, stomach.
  2. Midgut = small intestine and pancreas (herniated during development).
  3. Hindgut = colon 
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