Stage 1 (1rst day)1. Male pronucleus 2. Female pronucleus 3. Doubled paternal centrosome 4. "Inner bodies"

Stage 2 (2nd 3rd day)1. Zona pellucida 2. Blastomere 3. Polar bodyThe axis (dashed) lies through the two future (embryonic and abembryonic) poles. The embryo is divided into right and left halves (A and B).

Stage 3a (4th day)1. Embryoblast 2. Zona pellucida3. Trophoblast 4. Blastocyst cavity

Stage 3b (5th day)1. Decomposed zona pellucida with hatching blastocyst 2. Trophoblast cells 3. Hypoblast4. Blastocyst cavity 5. Epiblast

Stage 4 (6th day)1. Epithelium of the uterine mucosa 2. Hypoblast 3. Syncytiotrophoblast4. Cytotrophoblast 5. Epiblast

Stage 5a (7th 8th day)1. Syncytiotrophoblast 2. Cytotrophoblast 3. Hypoblast 4. Epiblast

5 6 7 Blastocyst cavity Amniotic cavity Maternal blood vessels

Stage 5b (9th day)

1 2 Lacunar trophoblast Definitive amniotic cavity

3 4 Primary yolk sac Maternal blood vessels

Stage 5c (11th 13th day)

1 2 3Extraembryonic mesoblast Amniotic cavity Primary yolk sac (= primary umbilical vesicle)

1 2 3Extraembryonic mesoblast Chorion cavity Secundary yolk sac(= secundary umbilical vesicle)

Stage 6 (17th day)

1 2 3 4 5 6 7 8 9 NBPrimitive groovePrimitive pit Primitive node Oropharyngeal membrane Cardial plate Cut edge of amniotic membrane Mesoderm Endoderm Future cloacal membrane 1+2+3 = primitive streak

Stage 7 (19th day;dorsal view)

1 2 3 4 Yolk sac Primitive streak Primitive node Embryonic disk

Stage 8 (23th day)

1 2 3 4 Body stalk Primitive streak Embryonic disk Cut edge of the amnion

Stage 9 (25th day)

1 2 3 Primitive streak and primitive groove Neural folds Cut edge of the amnion

4 5Neural groove Somites

Stage 10a, 10b (28th day)

1 2a 3 4 Cut edge of the amnion Neural groove Neural folds Somites

2b 2c 2d 5Neural tube Caudal neuropore Rostral neuropore Yolk sac

Stage 11 (29th day)1. Neural tube 2. Caudal neuropore 3. Rostral neuropore that is just closing4. Somites 5. 2. pharyngeal arch 6. 1. pharyngeal arch

Stage 12 (30th day)1a. Maxillar process 1b. Mandibular process 2. Second pharyngeal arch 3. Third pharyngeal arch 4. Somites 5. Neural tube 6. HeartP : Prosencephalon (forebrain) M : Mesencephalon (midbrain) R : Rhombencephalon (hindbrain)

Stage 13 (32th daya)1a.Maxillary process 1b.Mandibular process 2. Second pharyngeal arch 3. Third pharyngeal arch 4. Fourth pharyngeal arch 5. Somites 6. Buds of the upper extremities 7. Left cardiac ventricle 8. Left cardiac atrium 9. Body stalk 10.Embryonic tail

Stage 14 (33th day)1.Telencephalon 2.Mesencephalon 3.Myelencephalon 4.Ocular primordium 5.Fourth ventricle 6.Cervical sinus 7.Mesonephric cord 8.Bud of the upper extremity 9.Bud of the lower extremity

Stage 15 (36th day)1.Umbilical cord 2.Cardiac prominence 3.Nasal placode 4.Ocular primordium 5.Bud of the upper extremity 6.Bud of the lower extremity

Stage 16 (39th day)1.Umbilical cord 2.Nasal pit 3.Nasolacrimal groove 4.Ocular primordium 5.Flexura pontina 6.Flexura cervicalis 7.Auditory primordium 8.Cardiac prominence 9.Hand plate 10.Foot plate

M : Telencephalon C : DiencephalonBM : MesencephalonA : MetencephalonB : MyelencephalonHj : Spinal cord

Stage 17 (41th day)1.Umbilical cord with physiologic umbilical hernia 2.Nasal pit 3.Pigmented lens placode 4.External acoustic meatus 5.Auricular hillocks 6.Formation of the interdigital zones

Stage 18 (44th day)1.Cardiac prominence 2.Nasolacrimal groove 3.External acoustic meatus 4.Hand plate with visible finger radiations 5.Footplate with toe primordium 6.Primordium of the palpebra (eyelid)

Stage 19 (46th day)1.Liver prominence 2.Primordium of the eyelid 3.Eye 4.External acoustic meatus 5.Shoulder 6.Finger 7.Toes that are forming 8.Straightening of the trunk

Stage 20 (49th day)1.Liver prominence 2.Primordium of the eyelid 3.Eye 4.Auditory canal 5.Elbow 6.Fingers 7.Toes being formed 8.Straightening of the trunk 9.Subcutaneous vessel network of the head 10.Cervical flexure

Stage 21 (51th day)1.Umbilical cord with physiologic hernia 2.Nose 3.Subcutaneous vessel network of the head 4.Ear 5.Elbow 6.Pronation of the hands (pink arrow) 7.Knee 8.Supination of the feet (blue arrow) 9.Toes

Stage 22 (53th day)1.Umbilical cord with physiologic hernia 2.Nose 3.Subcutaneous vessel network of the head 4.Ear 5.Elbow 6.Pronation of the hands 7.Knee 8.Supination of the feet 9.Well-developed toes 10.Remainder of the embryonic tail1.

Stage 23 (56th day)1.Umbilcal cord with hernia 2.Nose 3.Eye 4.Eyelid 5.Ear (a: tragus, b: antitragus ) 6.Mouth 7.Elbow 8.Finger 9.Toes 10.Atrophied embryonic tail bud

M : Telencephalon C : DiencephalonBM : MesencephalonA : MetencephalonB : MyelencephalonHj : Spinal cord

Teratology:medications, chromosomal abnormalities, environmental factors,infection.

Nondisjunction occurs whenchromosomes segregate in anaphasebefore the kinetochore of each sisterchromatid has attached tomicrotubules (red lines) from theopposite spindle poles. As a result,one daughter cell contains two copiesof one chromosome, while the otherdaughter cell lacks that chromosome.

Down syndrome - trisomy 21

Folic Acid and Neural Tube Defects

The placenta (Gk. plakuos= flat cake) is a mateno-fetal organ which beginsdeveloping at implantation of the blastocyst and is delivered with the fetus at birth.Placental Metabolism: synthesizes glycogen, cholesterol, fatty acids, providesnutrient and energy.Placental Transport: oxygen, carbon dioxide, carbon monoxidewater, glucose, vitamins, hormones, mainly steroid not protein, electrolytes, maternalantibodies, waste products, urea, uric acid, bilirubin, drugs and their metabolites(fetal drug addiction), infectious agents (cytomegalovirus, rubella, measles,microorganisms).Placental Endocrine: Human chorionic gonadotrophin (hCG, like leutenizinghormone, supports corpus luteum), Human chorionic somatommotropin (hCS, or placental lactogen, stimulate mammary development), Human chorionic thyrotropin(hCT), Human chorionic corticotropin (hCACTH), progesterone and estrogens(support maternal endometrium), relaxin.

Critical Periods of Human Development

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