Embryogenesis Timeline

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Embryogenesis Timeline by Mind Map: Embryogenesis Timeline

1. Day 1

1.1. Fertilization

1.1.1. Sperm enters secondary oocyte Corona radiata barrier ZP3 Binding to ZP and acrosomal reaction Acrosin Integrins on oocytes disintigrins on sperm Fusion of sperm to oocyte Permeability change of ZP

1.1.2. Oocyte completes meiosis II Male and female pronucleus form

1.1.3. Initiation of cleavage Two cells - 30 hours Four cell blastomeres - 40 hours

2. Day 4

2.1. Early Blastocyst

2.1.1. Embryoblast

2.1.2. Trophoblast

2.2. Hatches from the ZP

3. Day 6

3.1. Implantation

3.1.1. Endometrial cells of mother Pinapodes Leukemia inhibitory factor (LIF)

3.1.2. Cytotrophoblast expresses the LIF receptor

3.1.3. Blastocyst adheres to endometrium Starts producing own LIF

3.1.4. Endometrium produces additional attachment and tropic factors Glycoprotein 130

4. Day 3

4.1. Morula

4.1.1. Compaction of embryoblast 8-16 cells

5. Day 5

5.1. Late Blastocyst

5.1.1. Embryoblast begins to differentiate Hypoblast Epiblast

6. Day 8

6.1. Bilaminar Disc

6.1.1. Embryoblast Layer of columnar Epiblast cells Layer of cuboidal Hypoblast cells

6.1.2. Trophoblast Syncytiotrophoblast Interleukin-1 Cytotrophoblast

7. Day 16

7.1. Gastrulation

7.1.1. The streak is now clearly visable Slightly bulging lesions on either side

7.1.2. Primitive node cephalic end Slightly elevated area surrounding primitive pit

7.1.3. Invagination Fibroblast Growth Factor 8 (FGF8) Controls cell growth and differentiation Synthesized by streak cells themselves Downregulates E-cadherin Regulates BRACHYURY Cells of the epiblast migrate towards primitive streak Cells moving between the epiblast and hypoblast spread laterally and cranially These cells move beyond the margin of the disc and establish contact with the extraembryonic mesoderm covering the yolk sac and amnion Upon arrival in the region of the streak, they become flask-shaped, detach from the epiblast, and slip beneath it In the cephalic direction, they pass on each side of the prechordal plate. The prechordal plate itself forms between the tip of the notochord and the oropharyngeal membrane and is derived from some of the first cells that migrate through the node in the midline and move in a cephalic direction

7.2. allantois appears

8. Day 32

8.1. Embryo in chorionic cavity

9. Day 35

9.1. Brachial arches & clefts

10. Day 37

10.1. Developing face

11. Day 36

11.1. Physiological umbilical hernia

12. Day 28

12.1. Neurulation complete

13. Day 29

13.1. Arm and leg buds

14. Day 13

14.1. Uretoplacental circulation begins

14.2. surface defect in the endometrium has usually healed

14.3. Bleeding may occur at this stage

14.3.1. It may be mistaken for menstruation

14.4. Primary villi forms

14.4.1. This (over time) will begin to protrude outward all the way to the uterine tissue over the syncytiotrophoblast

14.4.2. Will continue until differentiation and formation of villus the 4th week

15. Day 9

15.1. Lacunar Stage

15.1.1. Vacuoles appear in syncytium Vacuoles fuse, creating lacunae

15.2. The blastocyst is more deeply embedded in the endometrium; penetration defect in the surface epithelium is closed by a fibrin coagulum

15.3. Epiblast

15.3.1. migrate and form amnioblasts

15.4. Hypoblast

15.4.1. Migrate and attach to cytotrophoblast cells Line blastocyst cavity Forms exocoelomic membrane

15.5. Blastocyst cavity becomes primitive yolk sac

16. Day 17

16.1. Epiblast forms germ layers

16.1.1. Endoderm Cells that displace the hypoblast

16.1.2. Mesoderm Lies between the epiblast and newly created endoderm

16.1.3. Ectoderm Cells remaining in the epiblast

16.2. The oropharyngeal membrane (cranial end of the disc) forms - tightly adherent ectoderm and endoderm cells that represents the future opening of the oral cavity.

16.3. The most cranial portion of the definitive notochord has formed

17. Day 18

17.1. Trilaminar embryonic disc

17.2. Bone Morphogenetic Protein 4 (BMP 4)

17.2.1. Member of the TGF-β family

17.2.2. Is secreted through the disc

17.2.3. Ventralizes mesoderm Would ventralize everything if it wasn't stopped by other genes

17.2.4. Antagonists: CHORDIN Activated by GOOSECOID noggin follistatin

18. Day 26

18.1. Pharyngeal arches present

19. Day 24-25

19.1. Villus formation

19.1.1. Mesodermal cells in villus core differentiate into blood cells and smaller blood cells Forms the villus capillary system

19.1.2. Villus is now a tertiary villus or definitive placental villus

19.2. Cranial end of pore closes first

20. Day 20

20.1. Neurulation

20.1.1. Neural groove and neural folds

20.2. Somites first appear

20.2.1. This continues ~ 3 somites a day

20.2.2. Appears first in occipital region

21. Day 14

21.1. Embryonic Disc

21.2. Enough hCG for a pregnancy test

21.3. Bilaminar disc splitting identical twins at this stage

21.3.1. occurs just before appearance of primitive streak

21.3.2. Extremely rare

21.3.3. Will form identical twins in the same placenta with common chorionic and amniotic sacs

22. Day 30

22.1. Developing face

23. Day 33

23.1. Umbilical ring

24. Day 23

24.1. Neural tube zippers

24.2. Embryo will be straight and slightly curved

24.2.1. still open on caudal end

25. Day 31

25.1. Gut development

26. Day 34

26.1. optic cup & lens placode

27. Day 19

27.1. CNS Induction

27.1.1. Neural tube is the precursor of the CNS

27.2. Amnion removed

27.2.1. Neural plate clearly visable

27.3. Embryo is attached to the chorionic plate via the connecting stalk

27.3.1. Later develops into umbilical cord

28. Day 15

28.1. Primitive streak begins to form

28.1.1. Marks the beginning of gastrulation

28.1.2. Primitive groove

28.1.3. Primitive node

28.1.4. Primitive pit

28.2. Laterally established

28.2.1. Streak is initiated and maintained by epiblast cells Nodal upregulates genes responsible for dorsal and ventral mesoderm accumulates on left side near the node to establish left and right sidedness epithelial-mesenchymal transformation ingression of cells between the epiblast and hypoblast This takes place days 16-17 to form trilaminar disc

29. Day 10-11

29.1. Blastocyst completely embedded in endometrium stroma

29.1.1. now produces a slight protrusion into the lumen of the uterus

29.2. surface epithelium almost entirely covers the original defect in the uterine wall

29.3. Embryonic Pole

29.3.1. Trophoblast characterized by lacunae in syncytium Form intercommunicating network

29.4. Aembryonic Pole

29.4.1. Trophoblast still consists of mainly cytotrophoblastic cells

29.5. Syncytiotrophoblast penetrates deeper into the stroma

29.5.1. Erosion of maternal capillary endothelial lining Formation of sinuses Becomes part of lacunae Establishment of uretoplacental circulation

30. Day 21

30.1. Transverse section

30.2. Beginning of third week of development

31. Day 12

31.1. Extraembryonic mesoderm forms

31.1.1. Derived from yolk sac cells

31.1.2. Fine, loose connective tissue

31.1.3. Between the inner surface of the cytotrophoblast and the outer surface of the exocoelomic cavity

31.1.4. FIlls all of the space between the trophoblast externally and the amnion and exocoelomic membrane internally

31.1.5. large cavities develop, combine, and soon form extraembryonic cavity Also called chorionic cavity This space surrounds the primitive yolk sac and amniotic cavity This space will later be eradicated by amniotic cavity growth due to the fusion of amnion and chorion to form anmniochorionic membrane the amniochorionic membrane is what ruptures during labor

31.1.6. Extraembryonic somatic mesoderm Lines the cytotrophoblast and amnion

31.1.7. Extraembryonic splanchnic mesoderm Lines the yolk sac

31.2. Growth of bilaminar disc slower at this stage than trophoblast

31.2.1. Decidua reaction Decidual cells degenerate adjacent to the syncytiotrophoblast and provide nutrition

31.3. hCG is secreted by syncytiotrophoblast

32. Day 22

32.1. Neural Tube closure begins