Basic embryology part i

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Basic embryology part i

  1. 1. Basic EmbryologyBasic Embryology PART I BASICBASIC EMBRYOLOGYEMBRYOLOGY PART IPART I
  2. 2. EmbryologyEmbryology  Embryology – study of the origin and development of single individual  Prenatal period  Embryonic period – first 8 weeks (56 days)  Fetal period – remaining 30 weeks (210 days) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  3. 3. Development of embryologyDevelopment of embryology  Aristotle, B.C 384-322 Semen+menstration  Harvey, 1651: All life from oocyte  Malpighi, 1675: A micro-chicken in an egg  Leewenhoek, 1677 : A micro-human in a sperm Haeckel, 1868 Biogenetic law Spemann, 1869-1941 Experimental embryology Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  4. 4. Embryonic Period Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.1 (1 of 2)
  5. 5. Fetal Period Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.1 (2 of 2)
  6. 6. The Basic Body PlanThe Basic Body Plan  Skin – dermis and epidermis  Outer body wall – trunk muscles, ribs, vertebrae  Body cavity and digestive tube (inner tube)  Kidneys and gonads – deep to body wall  Limbs Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  7. 7. The Basic Body Plan Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.2
  8. 8. The Embryonic PeriodThe Embryonic Period  Week 1 – from zygote to blastocyst  Conception – in lateral third of uterine tube  Zygote (fertilized oocyte) moves toward the uterus  Blastomeres – daughter cells formed from zygote  Morula – solid cluster of 12–16 blastomeres  “Mulberry”  Blastocyst – fluid-filled structure – ~ 60 cells Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  9. 9. The Embryonic PeriodThe Embryonic Period  Stages of first week  Zygote  4-cell  Morula  Early blastocyst  Late blastocyst (implants at this stage) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  10. 10. Fertilization & Its processFertilization & Its process Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings nucleus acrosome Penetration and release of acrosomal enzyme Cell membrane of ovum Sperm bind to sperm receptor ZP-3 induce Acrosome reaction : release of acrosomal enzyme
  11. 11. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings ovum sperm fertilized ovum
  12. 12. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Zona reaction: Cortical granules→perivitelline space →degrade ZP-3, alteration of zona pellucida →barrier for sperm penetration The second meiotic division of the secondary oocyte is rapidly lifted and the second polar body is released, leaving a haploid female nucleus.
  13. 13. Contac of sperm and ovumContac of sperm and ovum Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  14. 14. Sperm penetrate into the ovumSperm penetrate into the ovum Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  15. 15. Formation & Fusion of Male andFormation & Fusion of Male and Female PronucleiFemale Pronuclei Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  16. 16. Fertilization and the Events of theFertilization and the Events of the First 6 Days of DevelopmentFirst 6 Days of Development Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.3
  17. 17. Process of fertilizationProcess of fertilization Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings ① Fusion of the membrane of sperm and ovum ② The nucleus of sperm penetrate into ovum ③ Formation of pronuclei ④ Fusion of pronuclei Alteration of ovum
  18. 18. Week 2 – The Two-LayeredWeek 2 – The Two-Layered EmbryoEmbryo  Bilaminar embryonic disc – inner cell mass divided into two sheets  Epiblast and the hypoblast  Together they make up the bilaminar embryonic disc Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  19. 19. Week 2 – The Two-LayeredWeek 2 – The Two-Layered EmbryoEmbryo  Amniotic sac – formed by an extension of epiblast  Outer membrane forms the amnion  Inner membrane forms the amniotic sac cavity  Filled with amniotic fluid Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  20. 20. Week 2 – The Two-LayeredWeek 2 – The Two-Layered EmbryoEmbryo  Yolk sac – formed by an extension of hypoblast  Digestive tube forms from yolk sac  NOT a major source of nutrients for embryo  Tissues around yolk sac  Gives rise to earliest blood cells and blood vessels Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  21. 21. Implantation of the BlastocystImplantation of the Blastocyst Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.4 (1 of 3)
  22. 22. Implantation of the Blastocyst…Implantation of the Blastocyst… Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.4 (2 of 3)
  23. 23. Implantation of the Blastocyst…Implantation of the Blastocyst… Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.4 (3 of 3)
  24. 24. Week 3 – The Three-LayeredWeek 3 – The Three-Layered Embryo…Embryo…  Primitive streak – raised groove on the dorsal surface of the epiblast  Gastrulation – a process of invagination of epiblast cells  Begins at the primitive streak  Forms the three primary germ layers Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  25. 25. Week 3 – The Three-LayeredWeek 3 – The Three-Layered Embryo…Embryo…  Three Germ Layers*  Endoderm – formed from migrating cells that replace the hypoblast  Mesoderm – formed between epiblast and endoderm  Ectoderm – formed from epiblast cells that stay on dorsal surface *All layers derive from epiblast cells! Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  26. 26. The Primitive StreakThe Primitive Streak Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.5e–h
  27. 27. The NotochordThe Notochord  Primitive node – a swelling at one end of primitive streak  Notochord forms from primitive node and endoderm  Notochord – defines body axis  Is the site of the future vertebral column  Appears on day 16 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  28. 28. Formation of the Mesoderm and NotochordFormation of the Mesoderm and Notochord Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.6
  29. 29. NeurulationNeurulation  Neurulation – ectoderm starts forming brain and spinal cord  Neural plate – ectoderm in the dorsal midline thickens  Neural groove – ectoderm folds inward Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  30. 30. NeurulationNeurulation Neurulation (continued)  Neural tube – a hollow tube pinches off into the body Cranial part of the neural tube becomes the brain Maternal folic acid deficiency causes neural tube defects Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  31. 31. NeurulationNeurulation  Neural crest  Cells originate from ectodermal cells  Forms sensory nerve cells  Induction  Ability of one group of cells to influence developmental direction of other cells Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  32. 32. The Mesoderm Begins toThe Mesoderm Begins to DifferentiateDifferentiate  Somites – our first body segments  Paraxial mesoderm  Intermediate mesoderm – begins as a continuous strip of tissue just lateral to the paraxial mesoderm Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
  33. 33. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings  Lateral plate – most lateral part of the mesoderm  Coelom – becomes serous body cavities  Somatic mesoderm – apposed to the ectoderm  Splanchnic mesoderm – apposed to the endoderm The Mesoderm Begins toThe Mesoderm Begins to DifferentiateDifferentiate
  34. 34. Basic EmbryologyBasic Embryology PART II & III WILL BE COMING SHORTLY BY NEXT LECTURE IN SHAA ALLAH. THANK YOU ALL FOR ATTENDING THIS LECTURE

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