1. HUMAN
EMBRYOLOGY

2. PERIODS OF EMBRYOGENESIS
1. FERTILIZATION AND ZYGOTE FORMATION
2. CLEAVAGE
3. GASTRULATION.
4. HISTO- AND ORGANOGENESIS

3. CHARACTERISTICS OF GAMETES
OOCYTE SPERMATOZOA

4. CHARACTERISTICS OF GAMETES

5. FERTILIZATION

6. FERTILIZATION

7. FERTILIZATION

8. CLEAVAGE

9. CLEAVAGE

12. IMPLANTATION

14. EARLY GASTRULATION

15. EXTRAEMBRYONIC ORGANS
FORMATION

16. LATE GASTRULATION

19. DIFFERENTATION OF GERM LAYERS

24. 22-23 days pf Human

25. 23-26 days pf Human

26. Formation of the Neural Tube
• Secondary Neurulation
1. Occurs beyond the caudal neuropore
2. lumbar and tail region
3. Exclusive mechanism for fish
4. Starts with formation of medullary cord
5. Cavitation of cord to form hollow tube

27. Differentiation of Neural Tube
• Major morphological changes: differentiation of
brain vesicles and spinal cord
• Differentiation of neural tube cells
• Development of peripheral nervous system

32. Neural Crest Cells
• Migration:
– Epithelial to mesenchyme transition
– Migrational pathways are established by juxtacrine
signals:
• Fibronection, laminin in ECM + integrins
• Ephrin proteins: Restrict movement
• Contact inhibition
• Use of existing structures
– Migration ceases when these signals are reversed

33. Neural Crest Cells
• Differentiation:
– Largely based on location along neural tube and their
migration route:

34. Neural Crest Cells
• Differentiation:
– Migration routes along trunk:
– Ventral pathway: cells move through anterior portion of
somite toward ventral side of embryo
• Cells become: sensory neurons, sympathetic
ganglia, medulla of adrenal gland
– Dorsolateral pathway: cells move between epidermis
and somite
• Cells become: melanocytes
• Basic organization of the PNS is established by the
migratory pathways of the neural crest cells