General Embryology 3 (Intraembryonic mesoderm , Endoderm , Embryonic folding)

This presentations shows during pregnancy what is Intraembryonic mesoderm formation & classification , Endoderm fate , and Embryonic folding steps & results

Transcript

1. Intra-Embryonic Mesoderm
2. Formation of Intra- Embryonic Mesoderm
3. Bucco- pharyngeal membrane Cloacal membrane Primitive streak Primitive node Developing notochord Developing intraembryonic mesoderm
4. At 17th Day
5. Differentiation of Intra-embryonic Mesoderm Intra-embryonic mesoderm on each side of notochord, divides into: 1- Paraxial Mesoderm: on both sides of notochord. 2- Intermediate Mesoderm: Middle part of the mesoderm. 3- Lateral plate Mesoderm: Lateral part which communicates with that of the opposite side cranial to bucco-pharyngeal membrane.
6. Notochord Paraxial mesoderm Intermediate mesoderm Lateral plate mesoderm Removed ectoderm & neural tube
7. Fate of Intra-embryonic Mesoderm 1- Fate of paraxial mesoderm (Somites). 2- Fate of Intermediate mesoderm. 3- Fate of lateral plate mesoderm.
8. Paraxial Mesoderm (Somites)
9. Notochord Paraxial mesoderm Intermediate mesoderm
10. Notochord Somites of Paraxial mesoderm Dr.Sherif Fahmy Day 20 Day 21 Day 22
11. Somites Origin: from segmented paraxial mesoderm. Number: 42 – 44 pairs Types (regional classification): 4 occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral & 8 – 10 coccygeal. Time: • 1st pair at the 20th day. • 3 pairs each day till the 30th day (Somite period). • Then the rest is completed till 35 – 40 days but in a slower rate. N.B. Somitomeres are parts of paraxial mesoderm in head.
13. Calculation of the Age of Embryo From the Number of Somites.
14. Age of Embryo (days) = Number of somites - 1 + 20 3
15. Fate of Somites
16. Some Anatomical Facts
17. Spinal cord Body of a vertebra Intervertebral disc Vertebral (neural) arch Nucleus pulposus
18. Ventro-medial part (Sclerotome) Dorsolateral part (Dermo-myotome) Somite Ventral Dorsal Dr. Sherif Fahmy
19. Notochord Neural tube Somite Sclerotome Myotome Dermatome Neural tube Body of vertebra & Intervertebral discs Skeletal muscles of the body and limbs Dermis Dermo-myotome Neural arch Transverse section of Folded Embryo Dr. Sherif Fahmy
20. Muscles of back Muscles of anterolateral aspect of body Muscles of limb Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Dermo-myotomes of upper limb Somitomeres Dr. Sherif Fahmy
21. Fate of Somites Each somite divides into Sclerotome and Dermo- myotome. 1- Sclerotome: It is ventro-medial part that form vertebral column and inter-vertebral discs around notochord and neural tube. 2- Dermo-myotome: It is the dorso-lateral part which subdivided into: A- Dermatome: Forms dermis of skin. B- Myotome: Forms skeletal muscles of trunk and limbs.
22. Intermediate Mesoderm
23. 2-Intermediate Mesoderm •It forms uro-genital system.
24. Lateral Plate Mesoderm
25. Bucco-pharyngeal membrane Lateral plate mesoderm
26. Dr.Sherif Fahmy Intra-embryonic coelom
27. Intraembryonic coelom Pericardium Pleura Peritoneal canal Septum transversum Dr.Sherif Fahmy
28. Ectoderm Somatic mesoderm Endoderm Splanchnic mesoderm Splanchnic mesoderm Somatic mesoderm After Folding Dr. Sherif Fahmy
29. Fate of Endoderm
30. Development of Endoderm It gives rise to: 1-Epithelium (mucus lining) of: a-Digestive canal except its terminal parts. b-Respiratory tract. c-Most of urinary bladder and urethera. d-Tympanic cavity and Eustachian tube. 2- Parenchyma of: -Liver, pancreas, thyroid, thymus, palatine tonsils, and parathyroid glands.
31. Folding
32. Embryonic Disc
33. Definition: It is the process by which the embryo becomes folded upon itself. Time of folding: • From the end of 3rd week to the end of 4th week. Causes of folding: • Rapid increase of cranio-caudal length due to rapid growth of neural tube and somites. • Rapid expansion of amniotic cavity. Types of folding: • Head and tail folds are folding of cranial and caudal parts of the disc. Folds are limited by relatively firm notochord and primitive streak. • Lateral folds are folding of the sides of the embryonic disc in the transverse direction.
34. Steps of Folding
35. Steps of Folding A-Rapid expansion of amniotic cavity leads to: - Ventral shift of the amnio-ectodermal junction (towards endoderm) with dorsal bulge into amniotic cavity. B-Cranio-caudal elongation of embryonic disc leads to: -Formation of head & tail folds.
36. C-Lateral folds leads to: ➢ Formation of cylindrical shape embryo. ➢ Ectoderm on the outer surface. ➢ Mesoderm deep (internal) to ectoderm. ➢ Endoderm is innermost tube that forms the gut (Foregut, Midgut and Hindgut). ➢ Amniotic cavity surrounds the fetus and the umbilical cord.
37. Revision of the Embryonic Disc
38. Notochord Bucco- pharyngeal membrane Pericardium Septum transversum Primitive streak Peritoneal canals Cloacal membrane Connecting stalk Somites Pleura
39. Longitudinal Section of the Embryo During Folding
40. Connecting stalk
41. Dr. Sherif Fahmy
42. Dr. Sherif Fahmy
43. Transverse Section of the Embryo During Folding
44. Dr. Sherif Fahmy
45. Results of Folding
46. Connecting stalk Allantois Definitive yolk sac Vitelline duct Primitive umbilical ring Cylindrical embryo Amniotic cavity Dr. Sherif Fahmy
47. Ectoderm Mesoderm Endoderm Vitelline duct Allantois Definitive yolk sac L.S. in folded embryo Primitive umbilical ring Midgut
48. Buccopharyngeal membrane Cloacal membrane Hindgut Midgut Foregut Forebrain Forebrain bulge Pericardial bulge Stomodeum L.S. in folded embryo Heart Definitive yolk sac Vitelline duct Allantois Cloaca
49. Formation of Peritoneal Cavity and Mesentery
50. Peritoneal canals Gut Ventral mersentry Dorsal mesentry Transverse Section
51. RESULTS OF FOLDING 1-Cylindrical appearance: Transformation of embryonic disc to cylindrical shape. 2- Amniotic cavity: Before folding it lies dorsal to embryonic disc, after folding, it surrounds all aspects of the embryo. 3- Formation of primitive umbilical ring: It is a ventral defect in anterior abdominal wall that contains connecting stalk, allantois and vitello- intestinal duct 4- Formation of definitive yolk sac: It is the part of yolk sac outside the embryo in the umbilical cord.
52. 5-Formation of the gut: • It is formed from endodermal layer together with part of yolk sac. Foregut is formed in head fold with bucco-pharyngeal membrane closing its cranial end. Hindgut: is formed in tail fold and closed caudally by cloacal membrane. The caudal part is dilated and called cloaca with allantois connected to it. Midgut: is formed by lateral folds and present between foregut and hindgut. It is connected with defenitive yolk sac by vitelline duct.
53. 6- Formation of forebrain and pericardial bulges: Growing forebrain will form pericardial bulge while growing heart will form pericardial bulge. 7- Formation of stomodeum: It is ectodermal depression between forebrain and pericardial bulges. It is separated from foregut by bucco-pharyngeal membrane. 8- Formation of mesenteries: When peritoneal canals surrounds the gut, ventral and dorsal mesenteries are formed. 9- Reversal of positions: -Buccopharyngeal membrane becomes the most cranial, heart and pericardium become cranial to septum transversum (before folding septum transversum is most cranial). -Connecting stalk becomes ventral and more cranial in spite of being most