1. Stages of Human Development Ilse Pienaar Lecture 4 Embryology

2. Developmental Periods  Prenatal Period Developmental changes before birth Sperm Gr. sperma = seed Spermatozoon L. spermatos = seed; zōon = animal Zygote 1×sperm * 1×ovum = 1 cell An embryo Egg Oocyte Ovum (s), Ova (p) Stage 1

3. Developmental Periods  Gametogenesis Meiosis LL Stage 1 2*Diploid 46 X 2*Haploid 23 X

4. Developmental Periods- Meiosis I  Meiosis I Interphase Stage 1

5. Developmental Periods- Meiosis I  Meiosis I Prophase Stage 1

6. Developmental Periods- Meiosis I  Meiosis I Metaphase Stage 1

7. Developmental Periods- Meiosis I  Meiosis I Anaphase Stage 1

8. Developmental Periods- Meiosis I  Meiosis I Telophase Stage 1

9. Developmental Periods- Meiosis II  Meiosis II Prophase II Stage 1

10. Developmental Periods- Meiosis II  Meiosis II Metaphase II Stage 1

11. Developmental Periods- Meiosis II  Meiosis II Anaphase II Stage 1

12. Developmental Periods- Meiosis II  Meiosis II Telophase II Stage 1

13. Developmental Periods  End stage of Meiosis I & II 23 X Diploid 46 X 23 X Stage 1

14. Developmental Periods  Zygote Mitotic cell divisions / cleavage Stage 2 ZygoteMorula Early blastocyst Stage 3 Late blastocyst

15. Developmental Periods Stage 4 Implantation Gastrula

16. The Organogenic Period  Week 4 – 8 The major external and internal structures are established Minimal function

17. The Organogenic Period  Week 4 – 8  Phases of Embryonic Development Growth Stage 2Stage 3 Morphogenesis Differentiation Stage 1

18. Germ Layer Derivatives  Formed during gastrulation  Pimordia of all tissues and organs

19. Germ Layer Derivatives  Ectoderm Central Nervous System (CNS) Sensory epithelial  Eye, Ear, Nose, Epidermis, Hair, & Nails Mammary glands Pituitary gland Subcutaneous glands Teeth enamel Ectoderm Mesoderm Endoderm

20. Germ Layer Derivatives  NeuroEctoderm Neural Crest Cells Spinal Cranial  V, VII, IX, X Autonomic ganglia Ensheathing cells of PNS Muscle Connective tissues Meninges (brain & spinal cord) Ectoderm Mesoderm Endoderm

21. Germ Layer Derivatives  Mesoderm Connective tissue Cartilage Bone Muscle  Striated & smooth Heart Vessels  Blood & lymph Ectoderm Mesoderm Endoderm

22. Germ Layer Derivatives  Mesoderm Kidneys Ovaries & testes Genital ducts Serous membranes  Line body cavities  Spleen  Cortex of suprarenal glands Ectoderm Mesoderm Endoderm

23. Germ Layer Derivatives  Endoderm Epithelial lining  Gastrointestinal, respiratory tracts, tympanic cavity & bladder  Parenchyma of the tonsils  Thyroid and parathyroud glands  Thymus  Liver  Pancreas Ectoderm Mesoderm Endoderm

24. The Organogenic Period  Embryonic Folding From flat trilaminar embryonic disc Cylindrical embryo Median and Horizontal planes  Head Fold  Tail Fold Cranial Caudal Side

25. The Organogenic Period  Median Plane Folding The Head Fold  Brain: Primordium Developing forebrain grows beyond oropharyngeal membrane  Heart: Ventral move – septum transversum, primordial heart, pericardial coelom, oropharyngeal membrane  Foregut: Primordium of pharynx, esophagus… - lie between the brain and heart – develops into the central tendon of the diaphragm  Embryonic coelom – Primordium of body cavities

26. The Organogenic Period  Medial Plane Folding Tail fold  Growth of the distal part of the neural tube – primordium of the spinal cord  Caudal eminence projects over the claucal membrane  Part of the endodermal germ layer is incorporated into the embryo to become the hindgut – primordium of descending colon  Terminal part of cloaca dilates – primordium of urinary bladder and rectum

27. The Organogenic Period Horisontal Plane Folding  The Tail Fold Right and left lateral folds Produced by the rapidly growing spinal cord and somites Midgut: Primordium of small intestine – part of the endoderm germ layer is incorporated into the embryo Initial wide connection between the midgut and yolk sac

28. The Organogenic Period  Horisontal Plane Folding  The Tail Fold After folding – connection reduced Reduce communication between intra- and extraembryonic coelomic cavities