1. The document provides a general overview of human embryological processes including germ cell formation and fertilization, prenatal development through the formation of three layers, induction and differentiation, formation of the neural crest, and folding of the embryo. 2. Key stages discussed include gametogenesis, fertilization of the ovum by sperm to form a zygote, formation of the morula and blastocyst, implantation in the uterus, formation of the bilaminar and trilaminar germ discs, and development of the three germ layers and tissues from each layer. 3. Neural crest formation involves the development of the neural plate and tube from ectoderm and the migration of neural crest cells to

1. DHS 2 General Embryology Lecture 1 Original Lecture: Prof. Grant Townsend, University of Adelaide Dr. Sausan Al Kawas University of Sharjah

2. Objectives To provide a general description of human embryological processes as follows: Germ cell formation & fertilization Prenatal development Induction, competence, and differentiation Formation of three-layerd embryo Formation of neural crest Formation of human tissues Folding of the embryo Copyright © 2006/07 The University of Sharjah slide

3. Embryology Embryology is literally “the study of the embryo” More generally it refers to “the study of prenatal development” Embryo = 2-8 weeks Foetus = 9 weeks to birth Copyright © 2006/07 The University of Sharjah slide UNSW Embryology 2007

4. Embryology Ontogeny : stages of development of an individual Teratology : study of abnormal development (congenital malformations) Copyright © 2006/07 The University of Sharjah slide UNSW Embryology 2007

5. Mitosis and Meiosis Copyright © 2006/07 The University of Sharjah slide

6. Gametogenesis Gametogenesis is a process of formation and development of male(sperm) and female (ovum)gametes. During this process a reduction of the the number of chromosomes takes place from diploid number (46) of primary germ cells to the haploid number (23) in the mature germ cell. Copyright © 2006/07 The University of Sharjah slide

7. Gametogenesis It also involves the chromosomal and the cytoplasmic changes. These alteration of the shape of the primary germ cells allow them to become ready for fertilization. Copyright © 2006/07 The University of Sharjah slide

8. Gametogenesis The large rounded primary male germ cells, lose most of their cytoplasm and develop head, tail and neck to assist in the movement of the sperms. The rounded female germ cells become larger as a result of increase in the a mount of their cytoplasm and called ovum. Copyright © 2006/07 The University of Sharjah slide Mature sperm Mature oocyte

9. Fertilization The fertilization occur when sperm contacts an ovum to form a zygote in the uterine tube. The zygote, which contains 46 chromosomes, rapidly divide by mitosis to form mass of cells as 2,4, 8, 16, 32…. This mass of cells continue dividing in order to give the different tissues then organs of the human body. Copyright © 2006/07 The University of Sharjah slide Ref: Dental Embryology, Histology, and Anatomy

10. General Embryology Copyright © 2006/07 The University of Sharjah slide These images reproduced from Dr. Di Marzo Mature Human Egg Fertilized Human Zygote 4 Cell Human Embryo UNSW Embryology 2010

11. General Embryology Fertilization Zygote Genotype, environment, phenotype Induction, competence, differentiation Formation of the three layered embryo Morula, blastocyst, bilaminar then trilaminar germ disc Ectoderm, endoderm, mesoderm Formation of neural crest cells Folding of the embryo Copyright © 2006/07 The University of Sharjah slide

12. Copyright © 2006/07 The University of Sharjah slide

13. Copyright © 2006/07 The University of Sharjah slide . General Embryology Ref: Dental Embryology, Histology, and Anatomy Uterine tube Uterus Ovary

14. Copyright © 2006/07 The University of Sharjah slide General Embryology Ref: Dental Embryology, Histology, and Anatomy Division of the zygote Zygote. Formation of the morula Morula Blastula

15. Structure of the blastocyt (blastula): Copyright © 2006/07 The University of Sharjah slide

16. Copyright © 2006/07 The University of Sharjah slide Implantation of the blastocyte: Uterine wall Endometrium Digested endometrium Blastocyte

17. Copyright © 2006/07 The University of Sharjah slide Formation of embryonic layers: second week Ref: Dental Embryology, Histology, and Anatomy Bilaminar embryonic disc Secondary Yolk sac Endometrium Hypoblast amniotic cavity Epiblast

18. Copyright © 2006/07 The University of Sharjah slide Formation of the tri-laminar disc: Third week Formation of primitive streak at the midline causing the disc to have right and left half, each half will be as mirror to the other Primitive streak Bilaminar disc Epiblast layer Hypoblast layer

19. Copyright © 2006/07 The University of Sharjah slide Formation of primitive streak Formation of the tri-laminar disc: UNSW Embryology 2007

20. Copyright © 2006/07 The University of Sharjah slide Formation of the mesodermal layer: Movement of some cells of epiblast toward hypoblast at the primitive streak forms a third embryonic layer called mesoderm. Ectoderm layer Endoderm layer Mesoderm layer

21. Formation of Neural Crest Copyright © 2006/07 The University of Sharjah slide The nervous system develops as a thickening within ectoderm giving the neural plate.

22. Formation of Neural Crest Neural plate : w ill fold to form neural groove Neural groove : fuses to form neural tube Neural tube : Gives rise to brain and spinal cord Copyright © 2006/07 The University of Sharjah slide

23. Formation of Neural Crest Copyright © 2006/07 The University of Sharjah slide UNSW Embryology 2007

24. Copyright © 2006/07 The University of Sharjah slide Ref: Human Anatomy & Physiology/ Marieb

25. Formation of Neural Crest Neural crest cells migrate throughout the body and give rise to: Cranial and sensory ganglia and nerves Sympathetic neurones Schwann cells Pigment cells Meninges Cartilage of branchial arches Most of the connective tissue of the face “ectomesenchyme” Copyright © 2006/07 The University of Sharjah slide Ref: Avery (2003) Chapter 1992

26. Formation of Neural Crest Neural crest is essential in development of the face, neck and oral tissues. All tissues of a tooth and its supporting structures, except enamel, are derived from neural crest cells Copyright © 2006/07 The University of Sharjah slide Ref: Avery (2003) Chapter 1992

27. Copyright © 2006/07 The University of Sharjah slide The embryonic layers are distinct from each other and give rise to specific tissues such as: Nervous system. Sensory epi.of eye , ear & nose. Epidermis, hair and nails. Mammary & cutaneous glands. Epi.of sinuses,oral & nasal cavities . Intra-oral glands. Tooth enamel. Formation of the tissues: Ectoderm

28. Formation of the tissues: Copyright © 2006/07 The University of Sharjah slide Muscle tissue C.T Bone . Cartilage. Pulp. Dentin . Cementum. PL. Alveolar Bone . Mesoderm Ecto-mesoderm

29. Formation of the tissues: Copyright © 2006/07 The University of Sharjah slide GI tract epithelium & associated glands. Ref: Dental Embryology, Histology, and Anatomy Endoderm ECTODERM ENDODERM MESODERM

30. Folding of the embryo Folding in two planes: Along longitudinal axis to form the stomatodeum (primitive oral cavity) Copyright © 2006/07 The University of Sharjah slide Ref: Ten Cate (2003) Chapter 2

31. Folding of the embryo Copyright © 2006/07 The University of Sharjah slide Ref: Ten Cate (2003) Chapter 2 Along lateral axis to form the foregut. Completion of the embryonic period (2-8 week)

32. Copyright © 2006/07 The University of Sharjah slide Ten Cate (2003) Chapter 2

33. Copyright © 2006/07 The University of Sharjah slide Thank you