General Embryology 1

The presentation includes details & illustrations regarding the first 2 weeks of pregnancy and human development

Transcript

1. First Week of Development
2. First Week of Development ➢Fertilization. ➢Cleavage & Migration.
3. Fertilization
4. FERTILIZATION It is the process by which a sperm units with an ovum to form a zygote. Site: It occurs at ampulla of uterine tube (outer 1/3 of uterine tube).
5. Ampulla of Fallopian tube
6. Structure of Sperm & Oocyte Corona radiata Zona pellucida Cell membrane Secondary oocyte arrested in 2nd meiotic division Head (4 microns) Neck Middle piece (6 microns) Tail (45 microns) Nucleus (23 Ch) Acrosomal cap Nucleus (23 Ch) Minimal cytoplasm Mitochondrial sheath
7. Steps of Fertilization •Capacitation. •Three phases: first, second and third. •Events during and after entrance of the sperm.
8. Dr. Sherif Fahmy
9. Events that occur during and after entrance of the sperm
10. Cortical & Zona Reaction
11. Start of cortical reaction when the head of sperm starts penetration of ovum cell membrane Dr. Sherif Fahmy
12. ➢Enlargement of nucleus of sperm to form male pronucleus. ➢Secondary oocyte completes 2nd meiotic division to form nucleus of ootid (female pronucleus). ➢Fusion between male pronucleus and female pronucleus to form nucleus of zygote.
13. Results of Fertilization • Formation of zygot. • Restoration of diploid number (46 chromosomes). • Determination of sex. • Mitotic divisions (Cleavage) start, during which the zygote travels through uterine tube by help of cilia and contraction of uterine tube (migration).
14. Cleavage & Migration
15. Zygote 2-cell stage 4-cell stage 8-cell stage 16-cell stage (morula) Balstocyst Fertilization -Cleavage occurs by mitotic divisions of zygote to get smaller blastomeres inside a sheath of zona pellucida. -Migration depends on cilia and peristalsis of uterine tube. Zona pellucida Ampullary part of uterine tube Dr. Sherif Fahmy
16. 2-cell stage 4-cell stage 8-cell stage Morula Early blastocyst Blastocyst
17. Blastocyst
18. Blastocele Inner cell mass (Embryoblast) Outer cell mass (Trophoblast) Embryonic pole Abembryonic pole Blastocyst
19. Second Week of Development
20. Second Week of Development •Implantation (7th – 11th day). •Decidua is the endometrium after implantation. •Formation of chorionic vesicle (13th day).
21. Implantation • Dif.: It is the process by which blastocyst is embedded in the endometrium. • Timing: Starts at 7th day and completed at 11th day. • Site: usually at upper part of posterior wall of uterus near fundus. • Features of endometrium at time of implantation are increased cells, spiral glands, spiral arteries with arterio-venous anastomosis.
22. Dr. Sherif Fahmy
23. Steps of Implantation
24. Dr. Sherif Fahmy Blastocyst Fixation (adhesion) of embryonic pole (of blastocyst) to implantation site Endometrium
25. Dr. Sherif Fahmy Endometrium Syncytiotrophoblast Trophoblast Blastocyst
26. Dr. Sherif Fahmy Syncytiotrophoblast Cytotrophoblast (Embryonic disc (Epiblast & Hypoblast) Trophoblast Amniotic cavity Blastocele Endometrium 8th Day
27. 9th & 10th days Fibrin clot Dr.Sherif Fahmy Dr. Sherif Fahmy
28. Endometrial epithelium overgrows site of implantation At the 11th day
29. Changes of Blastocyst During Implantation 1.Trophoblast differentiates into outer syncytio- trophoblast and inner cytotrophoblast. 2.Formation of amniotic cavity at the 8th day and blastocele becomes primary yolk sac at the 9th day. 3.Formation of bilaminar embryonic disc (epiblast & hypoblast) from inner cell mass.
30. Abnormal Sites of Implantation 1- Ectopic pregnany: They are tubal, ovarian or omental (peritoneum). 2- Placenta praevia: Parietalis, marginalis and centralis.
31. Ectopic Pregnancy Dr. Sherif Fahmy
32. Parietalis Marginalis Centralis Placenta Previa Placenta Internal os Dr. Sherif Fahmy
33. Decidua
34. Decidua Definition: It is the endometrium after implantation. Features: Exaggerated secretory phase of endometrium. Increased thickness of endometrium. Increased size and number of endometrial cells. Increased secretion in the uterine glands. Increased spiral arteries with arterio-venous anastomosis.
35. Parts of decidua 1. Decidua basalis 2. Decidua capsularis 3. Decidua parietalis
36. Decidua basalis Decidua capsularis Decidua parietalis Uterine cavity Dr.Sherif Fahmy
37. Fate of decidua • Decidua basalis (decidual plate) shares in the formation of placenta. • Decidua capsularis and parietalis fuse together and expelled with placenta after delivery.
38. Decidua basalis Decidua parietalis Decidua capsularis Uterine cavity Fused decidua parietalis and capsularis Decidua basalis Placenta Dr. Sherif Fahmy
39. Changes of Blastocyst in the Second Week of Pregnancy
40. 7th day: Dr. Sherif Fahmy Dr. Sherif Fahmy
41. 8TH Day of Pregnancy Endometrium Syncytio-trophoblast Cyto-trophoblast Hypoblast Amniotic cavity Amnioblast Epiblast Blastocele Partial implantation Dr. Sherif Fahmy
42. 9th & 10th days Fibrin clot Primary yolk sac Heuser’s membrane Lacunar spaces Syncytio-trophoblast Hypoblast Amniotic cavity Epiblast Amnioblast Cyto-trophoblast Endometrial epithelium Completely embedded Dr. Sherif Fahmy
43. Syncytiotrophoblast Cytotrophoblast Endometrial arteriol Lacunae filled with maternal blood (utero-placental circulation) Extra- embryonic mesoderm Large spaces 11th & 12th Days Bilaminar embryonic disc Primary yolk sac Amniotic cavity Endometrial epithelium overgrows the fibrin clot Dr. Sherif Fahmy
44. 13th Day Extra-embryonic celom (Chorionic cavity) Exocelomic cyst (pinched off from yolk sac) 2dry yolk sac Amniotic cavity Somatic mesoderm Somatic mesoderm Splanchnic mesoderm Connecting stalk Primary chorionic villi Chorionic vesicle Endometrial epithelium covers fibrin clot Cytotrophoblast Chorion Dr. Sherif Fahmy