7 1/2 week embryo, 7.5 week embryo, seven and a half week embryo

Interactive Prenatal Development Timeline

[All ages refer to time since fertilization] [Features] [Help] [Tutorial] [Print preview] [PDF]

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0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12 12-16 16-20 20-24 24-28 28-32 32-36 36-38

Unit 1: The First Week
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	Unit 3: 2 to 3 Weeks
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(2 weeks, 4 days): Brain is first organ to appear Neural plate induced by notochordal process (2 weeks, 6 days): Forebrain, midbrain, and hindbrain Neural groove deepens substantially Three main divisions of brain

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	Unit 5: 4 to 5 Weeks
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(4 weeks, 3 days): Early eyes (4 weeks, 4 days): Brain enlarges 50% since Carnegie Stage 13 Brain: Cerebral hemispheres appear and begin rapid growth Brain: Lateral ventricles Hypothalamus (4 weeks, 5 days): Blood vessels penetrate diencephalon Optic chiasm Brain with five main sections First nerve fibers Most cranial nerves seen Synapses among motor neurons in spinal cord Third ventricle Less Events...

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	Unit 7: 6 to 7 Weeks
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(6 weeks, 2 days): Optic fibers Brainwave activity has begun Cerebrospinal fluid production begins (6½ weeks): The hands begin to move (6 weeks, 5 days): Circulus arteriosus (Circle of Willis) complete Occipital pole of cerebral hemispheres (7 weeks): Head rotates Leg movements

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	Unit 9: 8 to 9 Weeks
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(8½ weeks): Neurons synapse in cerebral cortex (marginal zone) (9 weeks): Bends hip & knee if sole of foot touched Drinking fluid is becoming routine Sucking the thumb The young fetus now sighs, stretches, moves the head, opens the mouth, and moves the tongue Tongue movement Face, hands, and feet sense light touch

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	Unit 11: 10 to 11 Weeks
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(11 weeks): The face now makes complex expressions Auditory cells: inner & outer hair cells

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	Unit 13: 3 to 4 Months
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(13 weeks): Most of body sensitive to touch (14 weeks): Girls move their jaws more than the boys do Light touch to mouth evokes turn toward stimulus 4-lobed cerebral cortex Cerebellum resembles adult structure (16 weeks): Quickening Hormonal stress response to invasive procedures Less Events...

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	Unit 15: 5 to 6 Months
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(22 weeks): Behavioral states (23 weeks): Brain weight 100 grams (24 weeks): Blink-startle response; females before males

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	Unit 17: 7 to 8 Months
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(30 weeks): 6-layered cerebral cortex (32 weeks): Memory - music preferences (32 weeks - 36 weeks): Prenatal food affects newborn taste preferences

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	Unit 19: 9 Months to Birth
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(38 weeks): Spinal cord ends at third lumbar vertebrae Brain weight 350 grams

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Fertilization

Week 1 ends

Play Movie - 1 to 2 weeks, implantation and HCG

Week 2 ends

Play Movie - 2 to 3 week embryo, amnion, germ layer

Week 3 ends

Play Movie - 3 to 4 week embryo, folding of the embryo

Week 4 ends

Play Movie - 4 to 5 week embryo, The Heart in Action

Week 5 ends

Play Movie - 5 to 6 week embryo, hand plates develop

Week 6 ends

Play Movie - 6 to 7 week embryo, hand movement

Week 7 ends

Play Movie - 7 to 8 week embryo, fingers, toes

Week 8 ends

Play Movie - 8 to 9 week fetus, reflexive movement

Week 9 ends

Play Movie - 9 to 10 week fetus, sucking, swallowing

Week 10 ends

Play Movie - 10 to 11 week fetus, eyes roll, yawns

Week 11 ends

Play Movie - 11 to 12 week fetus, nails, fingerprints

Month 3 ends

Play Movie - 3 to 4 month fetus, the rooting reflex

Month 4 ends

Play Movie - 4 to 5 month fetus, bronchial tree

Month 5 ends

Play Movie - 5 to 6 months fetus, responds to sound

Month 6 ends

Play Movie - 6 to 7 month fetus, response to light

Month 7 ends

Play Movie - 7 to 8 month fetus, behavioral states

Month 8 ends

Play Movie - 8 to 9 month fetus, firm hand grasp

Month 9 ends

Birth

107 events on this timeline

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Unit 2: 1 to 2 Weeks
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	Unit 4: 3 to 4 Weeks
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(3 weeks, 1 day): Primary head vein Neural tube (3 weeks, 3 days): Internal carotid arteries Neuropore (near brain) closes Notochord (3 weeks, 5 days): Brain involves 40% of neural tube Lowermost spinal cord formation begins Neural tube closes (lower back) (4 weeks): Cerebellum Fourth ventricle

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	Unit 6: 5 to 6 Weeks
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(5 weeks, 2 days): Circle of Willis almost complete All cranial nerves identifiable (5½ weeks - 6 weeks): Subtle movement begins (5 weeks, 5 days): Nerve cells differentiating (5 weeks, 6 days): Dura begins forming in basal area Frontal and temporal poles of cerebral hemispheres Somites: Pairs 38 and 39 Synapses in spinal cord between interneurons and primary afferent neurons (6 weeks): Synapses form in spinal cord Less Events...

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	Unit 8: 7 to 8 Weeks
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(7 weeks, 1 day): Sacrocaudal spinal cord formation (secondary neurulation) complete (7 weeks, 3 days): Cerebral hemispheres cover more than half of diencephalon (7½ weeks): Hands begin to touch face The hands touch each other as do the feet! (7 weeks, 5 days): Brain: Internal capsule with connections to epithalamus, dorsal thalamus, and mesencephalon Cerebral hemispheres cover 75% of diencephalon Cortical plate expanding rapidly (8 weeks): Complex response to touch More frequent hand-to-face contact Mouth opens & closes Squinting The embryo floats and rolls over in the womb Blood supply to the brain closely resembles adult pattern Cranial nerve distribution mimics adult pattern Retina: Four of the ten adult layers present "The hindbrain "presents striking resemblance to that of the newborn." Brain represents 43% of embryo Grey and white matter Right- and left-handedness emerges Less Events...

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	Unit 10: 9 to 10 Weeks
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(9½ weeks): I yawn when I want (9 weeks, 4 days): Yawns (10 weeks): Eyes roll downward reflexively Corpus callosum begins

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	Unit 12: 11 to 12 Weeks
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(12 weeks): Hands touch the mouth up to 50 times per hour There are taste buds all over the mouth Corpus callosum

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	Unit 14: 4 to 5 Months
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(17 weeks): Retina has discrete layers (18 weeks): Corpus callosum complete (19 weeks): Daily cycles in biological rhythms (20 weeks): Hearing and responding to sound begins Hearing and responding to sound begins Head circumference 20 cm

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	Unit 16: 6 to 7 Months
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(25 weeks): Rods & cones The ability to taste (26 weeks): The ability to smell has arrived (26 weeks - 38 weeks): Brain weight increases 400% to 500% (27 weeks): Pupils react to light (28 weeks): Distinguishes sounds of different frequencies Less Events...

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	Unit 18: 8 to 9 Months
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(36 weeks): Brain weight 300 grams

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Nervous	Cardiovascular	Muscular	Early Events
Special Senses	Respiratory	Skeletal	General
Blood & Immune	Gastrointestinal	Endocrine	Growth Parameters
Skin/Integument	Renal/Urinary	Reproductive	Movement

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Interactive Prenatal Development Timeline

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