1. Gastrulation and Neurulation (3rd and 4th Week of Human Development)

2. Gametogenesis of Germ Cells in the Male and Female

4. Summary of the Ovarian Cycle, Fertilization and Human Development during the First Week

5. Cleavage and Implantation

6. Implantation of the Blastocyst (Day 7)

7. By 9 Days, the Embryo is Completely Implanted in the Uterine Endometrium

8. Days 10-13 of Embryonic Development

9. Day 15 of Embryonic Development

10. Implantation: Days 7-14
Days 7-9
Days 12-14
Days 10-12

11. View of the Germ Disc at the End of the Second Week of Development

12. Gastrulation: Formation of Embryonic Mesoderm and Endoderm

13. Paths of Migration of the Ingressing Mesoderm

14. Formation of Notochordal Process

15. Differentiation of Mesoderm
Paraxial mesoderm Intermediate mesoderm Lateral plate mesoderm
Axial skeleton Urinary system Parts of the limbs
Voluntary muscles Part of the genital system Most of the dermis

16. Formation of Somites from Paraxial Mesoderm
1-7 Somitomeres give rise to the striated muscles of the face, jaw and throat
Remaining 30 give rise to axial skeleton and voluntary muscles of the neck,
body wall and limbs.

17. Gastrulation

18. Onset of Neurulation

19. Neurulation: Formation of the Neural Tube

20. Closure of the Neural Tube (Day 22)

21. Closure of the Neural Tube proceeds Bilaterally

22. Malformations of Neural Tube Closure (1 in 600 births)

23. Types of Spina Bifida

24. Neurulation: Formation of the Neural Tube

25. Neural Crest Derivatives

26. Review Events of Third Week
Gastrulation, Formation of Trilaminar Disc and Initial
Development of the Somites and Neural Tube
Events of Fourth Week
Differentiation of the Somites and the Nervous System

27. Remnants of the Primitive Streak may Persist and give rise to a Sacrococcygeal Teratoma (1 in 35,000 newborns)

28. Derivatives of the Three Germ Cell Layers
Endoderm Derivatives
Epithelium of GI tract and its associated glands as well as glandular cells of the liver and pancreas
Epithelium of the urachus and urinary bladder
Epithelium of respiratory passages; the pharynx, trachea, bronchi, and alveoli.
Epithelial parts of the tonsils, thyroid, parathyroids, tympanic cavity, thymus
Epithelial parts of anterior pituitary
   
Mesoderm Derivatives
Cardiovascular system
Cells of lymphatic system, spleen, adrenal cortex
Skeleton, Striated muscles and smooth muscle coats
Dermis of skin
Connective tissue and vessels associated with organs
Urogenital system (gonads, ducts and accessory glands)
Ectoderm Derivatives
Epidermis of skin, nails, hair, sweat, mammary and, sebaceous glands
CNS, PNS
Retina and lens of eye
Pupillary muscle of the iris (*this is the only muscle of ectodermal origin)
Pineal body, anterior and posterior pituitary, adrenal medulla, melanocytes, schwann cells, odontoblasts