embryology2
TRANSCRIPT
HUMAN EMBRYOLOGY
1. FERTILIZATION AND ZYGOTE FORMATION2. CLEAVAGE3. GASTRULATION.4. HISTO- AND ORGANOGENESIS
PERIODS OF EMBRYOGENESIS
CHARACTERISTICS OF GAMETES
OOCYTE SPERMATOZOA
CHARACTERISTICS OF GAMETES
FERTILIZATION
FERTILIZATION
FERTILIZATION
CLEAVAGE
CLEAVAGE
IMPLANTATION
EARLY GASTRULATION
EXTRAEMBRYONIC ORGANS FORMATION
LATE GASTRULATION
DIFFERENTATION OF GERM LAYERS
22-23 days pf Human
23-26 days pf Human
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
Differentiation of Neural Tube
• Major morphological changes: differentiation of brain vesicles and spinal cord
• Differentiation of neural tube cells• Development of peripheral nervous system
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
Neural Crest Cells
• Differentiation:– Largely based on location along neural tube and their
migration route:
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