EMBRYOLOGY

1. EMBRYOLOGY Dr.D.KRUPA DANIEL (Ph.D) Associate Professor of Anatomy

2. SPERMATOGENESIS

3. SPERMATOGENESIS

4. SPERM

5. SPERMIOGENESIS

6. PARTS OF SPERM

7. AXIAL FILAMENT

8. FEMALE REPRODUCTIVE SYSTEM

9. OOGENESIS

10. STAGES

11. OVULATION • Secondary oocyte covered by follicular cells , Cumulus oophorecus. • Follicular cells secrete actively Estrogen. • Day 14 ovulation takes place. • Graffian follicle enlarges,bulges on the surface of the ovary and burst open. • By the time ovum is surrounded by Corona radiata cells. • Ovum is released into the peritoneal cavity and is taken up by fimbriated end of Uterine tube. • Sudden dip &raise of body temperature,mild pain in abdomen at the of ovulation.

12. CORPUS LUTEUM • The empty graffianfollice is converted into corpus luteum. • C.L lasts for 10 -12 days,if Ovum is not fertilized. • C.L lasts for 2-3 months,if ovum is fertilized and pregnancy continues. • Cells of Graffian follicle secretes Estrogen. • Cells of Corpus luteum secrete Progesterone.

13. Layers of Uterine Wall • Outer wall : Perimertium • Middle wall : Myometrium • Inner wall : Endometrium • Endometrium consists of lining epithelium which is columnar. • Endometrial Dip – Invagination. • Glands are formed & projects into Myometrium,Perimetrium.

14. PARTS

15. Endometrial Layer • Basal layer is thick and supporting the superficial layers. • Endometrium shows 3-parts. • Stratum Basale : Thin,Outer layer • Stratum Spongiosum : Thick,Middle layer • Stratum Compactum : Thin, Inner layer. • S.basale permanently present throughout cycle. • S.c & S.s are shed during Menstruation. • B.S : Uterine artery-Spiral arteries.

16. Endometrial Layer

17. Early Development of Embryo • Secondary oocyte is covered by Acellular,Amorphous Glycoprotein layer called ZONA PELLUCIDA. • Zonapellucida is covered by Corona radiata cells.

18. PHASES OF FERTILIZATION • Passage of Sperm through Corona Radiata. • Penetration of Zonapellucida. • Fusion of plasma membranes of the Oocyte and sperm. • Completion of 2nd meiotic division of oocyte &formation of female pronucleus. • Formation of Male pronucleus • Fusion of both Male & Female Pronuclei. • Zygote has formed (2n)

19. Phases of Fertilization

20. Phases of Fertilization

21. Penetration

22. Penetration

23. Penetration

24. Cleavage of Zygote

25. Cleavage of Zygote

26. Cleavage of Zygote

27. 2 – celled stage

28. 4-celled stage

29. 2,4,8,16 celled stage

30. FORMATION OF BLASTOCYST • 16 – celled stage is called MORULA. • Morula is converted to Blastocyst. • As the Morula moves towards the uterine cavity,fluid enters the Morula through zonapellucida and partially seperates the cells into Outer cell mass and inner cell mass. • As fluid as entered a cavity is formed. • Cavity enlarges ,Outer cell mass becomes flattened called as Trophoblast. • Inner cell mass is called Embryoblast. • This results in the formation of BLASTOCYST.

31. BLASTOCYST

32. BLASTOCYST • Blastocyst enlarges &Zonapellucida disappears. • Blastocyst is now Implanted in the wall of the uterus. • Trophoblast forms future Placenta. • Inner cell mass forms Embryo proper.

33. FIRST WEEK ENDS

34. SECOND WEEK

35. IMPLANTATION • Implantation is completed by the end of 2nd week-time between 6-10 days after Ovulation. • Trophoblast differentiates into outer synctiotrophoblast and inner Cytotrphoblast cells. • Synctiotrophoblast invades the Endometrial wall layer and the Blastocyst is Superficially Implanted by the end of SECOND WEEK. • Synctiotrophoblast secretes Human chorionic gonadotrophin hormone. • 9th Day.

36. IMPLANTATION

37. FORMATION OF GERM LAYERS • Bilaminar Germ Disc • Ectoderm • Endoderm • Amniotic cavity • Primary yolk sac

38. Prochordal plate • 14th day Embryo has a flat Bilaminar Germ disc. • At one end of embryonic disc near its margin a round area becomes thicker than the rest of the disc.The rounded area is called Prochordal plate. • In this region flattened endodermal cells becomes Columnar and are firmly adherent to ectoderm. • With the formation of prochordal plate the cranial & caudal ends of embryonic disc is identified.

39. Prochordal Plate

40. SECOND WEEK ENDS

41. THIRD WEEK

42. DURING 3RD WEEK • Appearance of Primitive Streak. • Differentiation of Three germ layers. • Notochord • Neural plate • Neural tube • Formation of Intra-embryonic mesoderm.

43. PRIMITIVE STREAK • Beginning of 3rd week & dissapears by end of 4th week. • Longitudinal ridge or elevation that appears at caudal end of embryo. • Primitive streak visible on the upper surface towards the amniotic cavity of Embryonic disc. • Ectodermal cells proliferates and move towards the midline and the cells elevates to form an elevation called as PRIMITIVE STREAK. • Intially it is at Caudal end.. Now it elongates Cranially. • At the cranial end Primitive streak proliferate to form PRIMITIVE NODE or KNOT or Hensen’s node.

44. PRIMITIVE STREAK • Primitive streak invaginate deep between ectoderm and endoderm.These cells extends now and forms Intraembryonic Mesoderm. • Anterior to Prochordal plate the Mesoderm of two sides is continous with each other to form SEPTUM TRANSVERSUM. • Now embryonic disc enlarges and becomes pear shaped. • Cranial end is Broad & Caudal end is narrow. • At caudal end IEM passes beyond embryonic disc and becomes Connective stalk. (EXTRA EMBRYONIC MESODERM) • Primitive streak after giving rise to MESODERM gradually disappears.

45. PRIMITIVE STREAK

46. SacrococcygealTeratoma • Remants of Primitive streak persists and gives rise to Sacrococcygealteratoma. • Common in New borns. • Prevalence : 1:35,000 • Affected : 80 % female babies. • Surgically excised.

47. NOTOCHORD NEURAL TUBE Intra embryonic mesoderm

48. Third week

49. THIRD WEEK ENDS

50. FOURTH WEEK • Embryo is straight. • Has 12 somites. • Neural tube formed. • Day :24 – First & Second arch develops. (Mandibular,Hyoid). • Maxillary prominence starts – upper jaw formation. • Now embryo is slightly folded due to Head & Tail folds. • Day :26 – 3 pairs of pharyngeal arches are visible. • Day : 26 – RostralNeuropore closes. • Forebrain starts developing.