1. Day 1
1.1. Fertilization
1.1.1. Sperm enters secondary oocyte
1.1.1.1. Corona radiata barrier
1.1.1.1.1. ZP3
1.1.1.2. Binding to ZP and acrosomal reaction
1.1.1.2.1. Acrosin
1.1.1.2.2. Integrins on oocytes
1.1.1.2.3. disintigrins on sperm
1.1.1.3. Fusion of sperm to oocyte
1.1.1.3.1. Permeability change of ZP
1.1.2. Oocyte completes meiosis II
1.1.2.1. Male and female pronucleus form
1.1.3. Initiation of cleavage
1.1.3.1. Two cells - 30 hours
1.1.3.2. 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
3.1.1.1. Pinapodes
3.1.1.1.1. Leukemia inhibitory factor (LIF)
3.1.2. Cytotrophoblast
3.1.2.1. expresses the LIF receptor
3.1.3. Blastocyst adheres to endometrium
3.1.3.1. Starts producing own LIF
3.1.4. Endometrium produces additional attachment and tropic factors
3.1.4.1. Glycoprotein 130
4. Day 3
4.1. Morula
4.1.1. Compaction of embryoblast
4.1.1.1. 8-16 cells
5. Day 5
5.1. Late Blastocyst
5.1.1. Embryoblast begins to differentiate
5.1.1.1. Hypoblast
5.1.1.2. Epiblast
6. Day 8
6.1. Bilaminar Disc
6.1.1. Embryoblast
6.1.1.1. Layer of columnar Epiblast cells
6.1.1.2. Layer of cuboidal Hypoblast cells
6.1.2. Trophoblast
6.1.2.1. Syncytiotrophoblast
6.1.2.1.1. Interleukin-1
6.1.2.2. Cytotrophoblast
7. Day 16
7.1. Gastrulation
7.1.1. The streak is now clearly visable
7.1.1.1. Slightly bulging lesions on either side
7.1.2. Primitive node
7.1.2.1. cephalic end
7.1.2.2. Slightly elevated area surrounding primitive pit
7.1.3. Invagination
7.1.3.1. Fibroblast Growth Factor 8 (FGF8)
7.1.3.1.1. Controls cell growth and differentiation
7.1.3.1.2. Synthesized by streak cells themselves
7.1.3.1.3. Downregulates E-cadherin
7.1.3.1.4. Regulates BRACHYURY
7.1.3.2. Cells of the epiblast migrate towards primitive streak
7.1.3.2.1. Cells moving between the epiblast and hypoblast spread laterally and cranially
7.1.3.2.2. These cells move beyond the margin of the disc and establish contact with the extraembryonic mesoderm covering the yolk sac and amnion
7.1.3.3. Upon arrival in the region of the streak, they become flask-shaped, detach from the epiblast, and slip beneath it
7.1.3.4. In the cephalic direction, they pass on each side of the prechordal plate.
7.1.3.4.1. 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
15.1.1.1. 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
15.4.1.1. Line blastocyst cavity
15.4.1.2. Forms exocoelomic membrane
15.5. Blastocyst cavity becomes primitive yolk sac
16. Day 17
16.1. Epiblast forms germ layers
16.1.1. Endoderm
16.1.1.1. Cells that displace the hypoblast
16.1.2. Mesoderm
16.1.2.1. Lies between the epiblast and newly created endoderm
16.1.3. Ectoderm
16.1.3.1. 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
17.2.3.1. Would ventralize everything if it wasn't stopped by other genes
17.2.4. Antagonists:
17.2.4.1. CHORDIN
17.2.4.1.1. Activated by GOOSECOID
17.2.4.2. noggin
17.2.4.3. 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
19.1.1.1. 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
28.2.1.1. Nodal
28.2.1.1.1. upregulates genes responsible for dorsal and ventral mesoderm
28.2.1.1.2. accumulates on left side near the node to establish left and right sidedness
28.2.1.2. epithelial-mesenchymal transformation
28.2.1.2.1. ingression of cells between the epiblast and hypoblast
28.2.1.2.2. 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
29.3.1.1. 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
29.5.1.1. Formation of sinuses
29.5.1.1.1. Becomes part of lacunae
29.5.1.1.2. 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
31.1.5.1. Also called chorionic cavity
31.1.5.2. This space surrounds the primitive yolk sac and amniotic cavity
31.1.5.3. This space will later be eradicated by amniotic cavity growth due to the fusion of amnion and chorion to form anmniochorionic membrane
31.1.5.3.1. the amniochorionic membrane is what ruptures during labor
31.1.6. Extraembryonic somatic mesoderm
31.1.6.1. Lines the cytotrophoblast and amnion
31.1.7. Extraembryonic splanchnic mesoderm
31.1.7.1. Lines the yolk sac
31.2. Growth of bilaminar disc slower at this stage than trophoblast
31.2.1. Decidua reaction
31.2.1.1. Decidual cells degenerate adjacent to the syncytiotrophoblast and provide nutrition