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Posted by on Sep. 27, 2011 at 10:14 AM
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Unit 1: The First Week

See Snapshots 

Play Movie - Cell Division

Play Movie

(Day 0 - Day 1)
General  Embryonic Period Begins

(Day 1 - Day 1)
Early Events  Fertilization - development begins with a single-cell embryo!!!
Early Events  Fertilization resulting in zygote formation

(Day 2)
Early Events  Activation of the genome

Early Events  Zygote divides into two blastomeres (perhaps 30 hours or so after fertlization)

(Day 2 - Day 2)
Endocrine  Early pregnancy factor (EPF)

(Day 3)
Early Events  Embryo is spherically shaped with 12 to16 cells

(Day 4)
Early Events  Embryonic disc
Early Events  Free floating blastocyst
Early Events  Inner cell mass
Early Events  See where the back and chest will be

(Day 5)
Early Events  Hatching

(Day 6)
Early Events  The embryo implants into wall of womb

(1 week)
Early Events  Chorion
Early Events  Hypoblast & epiblast
Early Events  Placenta begins to form

Take a quiz

-Week 1 ends-

Unit 2: 1 to 2 Weeks

See Snapshots

 Play Movie - 1 to 2 weeks, implantation and HCG

Play Movie

(1 week, 1 day)
Endocrine  Positive pregnancy test
Early Events  Amnioblasts present; amnion and amniotic cavity formation begins

(1 week, 2 days)
Early Events  Cells in womb engorged with nutrients

(1 week, 4 days)
Early Events  Longitudinal axis

(1 week, 5 days)
Early Events  Implantation complete
Early Events  Yolk sac

(1 week, 6 days)
Cardiovascular  Primordial blood vessels
Early Events  Amnion with single cell layer
Early Events  Chorionic villi

(2 weeks)
Early Events  Yolk sac

Take a quiz

-Week 2 ends-

Unit 3: 2 to 3 Weeks

See Snapshots

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

Play Movie

(2 weeks, 1 day)
Early Events  3 germ layers
Early Events  Rostral-caudal orientation

(2 weeks, 2 days)
Blood & Immune  Erythroblasts in yolk sac
Blood & Immune  Three types of blood-forming cells in yolk sac
Early Events  Amnion with two cell layers
Early Events  Secondary villi

(2 weeks, 4 days)
Gastrointestinal  Foregut, midgut, and hindgut
Nervous System  Brain is first organ to appear
Early Events  Connecting stalk

(2 weeks, 5 days
Nervous System  Neural plate induced by notochordal process

(2 weeks, 6 days)
Blood & Immune  Numerous blood islands in umbilical vesicle
Gastrointestinal  Foregut
Gastrointestinal  Stomodeum forming
Cardiovascular  Beginnings of the heart can be seen
Cardiovascular  Blood vessels emerge simultaneously in umbilical vesicle, embryo proper, amnion, and connecting stalk
Cardiovascular  Dorsal aortae (paired)
Cardiovascular  Paired tubular heart
Nervous System  Forebrain, midbrain, and hindbrain
Nervous System  Neural groove deepens substantially
Nervous System  Three main divisions of brain
Early Events  Neural crest: Rostral and facial

(3 weeks)
Cardiovascular  Blood and blood vessels

Take a quiz

-Week 3 ends-

by on Sep. 27, 2011 at 10:14 AM
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by Diane - Group Owner on Oct. 6, 2011 at 11:39 PM

Unit 4: 3 to 4 Weeks

See Snapshots

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

Play Movie

(3 weeks, 1 day)
Respiratory  Respiratory outgrowth
Cardiovascular  Circulatory system function begins
Cardiovascular  Heart begins beating
Cardiovascular  Tubular heart begins folding
Cardiovascular  Umbilical arteries
Cardiovascular  Umbilical veins (right and left)
Early Events  Body cavities

(3 weeks, 3 days)
Gastrointestinal  Liver
Gastrointestinal  Membrane between future mouth and throat may begin to rupture

(3 weeks, 5 days)
Gastrointestinal  First part of pancreas
Respiratory  Lung bud
Cardiovascular  Descending aorta
Nervous System  Lowermost spinal cord formation begins
Nervous System  Neural tube closes (lower back)
Early Events  Upper limb primordium at level of somites 8 to 10
General  Progressively C-shaped embryo

(4 weeks)
Skin  Skin is so thin, you can see through it!
Gastrointestinal  Esophagus primordia
Gastrointestinal  Pancreas: Ventral pancreas
Gastrointestinal  Pharynx
Gastrointestinal  Small & large intestines
Respiratory  Lungs begin filling chest cavity
Respiratory  Trachea
Cardiovascular  Circulatory system "well established"
Cardiovascular  Functioning two-chamber heart
Cardiovascular  Heart rate (about) 113 beats/min
Nervous System  Fourth ventricle
Early Events  Limb buds - the first sign of arms and legs
Early Events  Umbilical cord emerging
Early Events  Upper and lower limb buds

Take a quiz

-Week 4 ends-

Unit 5: 4 to 5 Weeks

See Snapshots

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

Play Movie

(4 weeks, 4 days)
Nervous System  Brain: Cerebral hemispheres appear and begin rapid growth

(4 weeks, 5 days)
Cardiovascular  Blood vessels penetrate diencephalon
Nervous System  Brain with five main sections
Nervous System  First nerve fibers

(5 weeks)
Respiratory  Lobar pattern mimics adult pattern
Cardiovascular  Pacemaker cells
General  Head is one third of entire embryo

Take a quiz

-Week 5 ends-

Unit 6:   5 to 6 Weeks

See Snapshots

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

Play Movie

(5 weeks, 2 days)
Nervous System  All cranial nerves identifiable

(5½ weeks)
Skeletal  Initial tooth formation

(5½ weeks - 6 weeks)
Movement  Subtle movement begins

(5 weeks, 6 days)
Gastrointestinal  Primordial vermiform appendix

(6 weeks)
Movement  Face withdraws from light touch around mouth
Blood & Immune  Blood forming in liver
Skeletal  Tooth buds (primary teeth)
Gastrointestinal  Intestines fill base of umbilical cord

Take a quiz

-Week 6 ends-

by Diane - Group Owner on Oct. 6, 2011 at 11:44 PM

Unit 7:  6 to 7 Weeks

See Snapshots

Play Movie - 6 to 7 week embryo, hand movement

Play Movie

(6 weeks, 2 days)
Skeletal  Elbow regions sometimes identifiable
Gastrointestinal  Submandibular gland primordia
Nervous System  Brainwave activity has begun

(6½ weeks)
Movement  The hands begin to move
Skeletal  Bones first form in the collar bones and lower jaw

(6 weeks, 5 days)
Skeletal  Arms point forward
Skeletal  Beginnings of occipital and sphenoid bones
Skeletal  Humerus, radius, and ulna

(6 weeks, 6 days)
Gastrointestinal  Cloacal membrane ruptures

(7 weeks)
Movement  Head rotates
Movement  Leg movements
Reproductive  Ovaries
Muscular  Hiccups
Cardiovascular  The heart has four chambers and is nearly complete.
Cardiovascular  The heart rate peaks at 165 to 170 beats per minute.

Take a quiz

-Week 7 ends-

Unit 8: 7 to 8 Weeks

See Snapshots

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

Play Movie

(7 weeks, 1 day)
Skeletal  Upper limbs with slightly flexed elbows
Nervous System  Sacrocaudal spinal cord formation (secondary neurulation) complete

(7 weeks, 1 day - 8 weeks)
Gastrointestinal  Stomach: Folds in stomach wall

(7 weeks, 2 days)
Cardiovascular  Arteries and veins of heart complete

(7 weeks, 3 days)
  Eyelids growing rapidly

(7½ weeks)
Skin  Fingertips thicken
Skeletal  The knee joints have arrived
Cardiovascular  EKG pattern similar to adult

(7 weeks, 4 days)
Skeletal  The fingers are free

(7 weeks, 5 days)
Skeletal  Bone-forming cells emerge
Skeletal  Hands can reach one another and fingers can overlap

(8 weeks)
Movement  Complex response to touch
Movement  More frequent hand-to-face contact
Renal/Urinary  Urine production and release
Respiratory  Occasional breathing motions begin
Cardiovascular  Blood supply to the brain closely resembles adult pattern
Special Senses  Ear drum
Nervous System  "The hindbrain "presents striking resemblance to that of the newborn."
Nervous System  Brain represents 43% of embryo
Nervous System  Right- and left-handedness emerges
General  Embryonic Period Ends

Take a quiz

-Week 8 ends-

-Embryonic Period ends and the Fetal Period begins-

by Diane - Group Owner on Oct. 10, 2011 at 1:00 AM

Unit 9:  8 to 9 Weeks

See Snapshots

Play Movie - 8 to 9 week fetus, reflexive movement

Play Movie

(8 weeks, 1 day): Fetal Period Begins
(8½ weeks)
  Eyelids completely fused

Nervous System   Neurons synapse in cerebral cortex (marginal zone)

(9 weeks)
Movement  Bends hip & knee if sole of foot touched
Movement  Drinking fluid is becoming routine
Movement  Sucking the thumb
Movement  The young fetus now sighs, stretches, moves the head, opens the mouth, and moves the tongue
Movement   Tongue movement
Reproductive  Female fetuses have early reproductive cells in their ovaries

Endocrine  Thyroid gland weighs 2 grams
Gastrointestinal   Small intestine peristalsis
Nervous System  Face, hands, and feet sense light touch

(9 weeks - 10 weeks)
Respiratory  Early vocal cords

General  My weight will rise more than 75% this week

Take a quiz

-Week 9 ends-

Unit 10:  9 to 10 Weeks

See Snapshots

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

Play Movie

(9½ weeks)
Movement  I yawn when I want

(10 weeks)
Movement  Eyes roll downward reflexively

Blood & Immune  Palatine tonsils
Skin  Fingernails and toenails begin to grow!
Skin  Three-layered epidermis
Skin  Tiny unique fingerprints have arrived!
Skeletal  Now, all the bones are getting harder
Skeletal  Tooth buds (secondary teeth)
Renal/Urinary  Glomeruli formation begins
Gastrointestinal  Physiologic herniation ends
Nervous System  Corpus callosum begins
General  Crown-heel length 7.5 cm

Take a quiz

-Week 10 ends-

Unit 11:  10 to 11 Weeks

See Snapshots

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

Play Movie

(10½ weeks)
Skin  Volar and plantar pads regress

(11 weeks)
Movement  The face now makes complex expressions
Blood & Immune  Immunological competence
Skin  Intermediate layer

Skin  Nose & lips completely formed
Reproductive  Now you can tell if it's a girl or boy!
Endocrine  Thyroid gland weighs 12 grams
Gastrointestinal  Intestines absorb water & glucose

Special Senses  Auditory cells: inner & outer hair cells
General  Crown-heel length

(11 weeks - 12 weeks)
General  Weight increases by 60% this week

Take a quiz

-Week 11 ends-

by Diane - Group Owner on Oct. 10, 2011 at 2:00 PM

Unit 12:  11 to 12 Weeks

See Snapshots

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

Play Movie

(12 weeks)
Movement  Hands touch the mouth up to 50 times per hour
Blood & Immune  T lymphocytes leave thymus

Endocrine  Many different hormones are present in pituitary gland
Endocrine  Thyroid gland produces hormone
Palate fuses
Skeletal  Upper limbs reach final proportion
Renal/Urinary  Bladder resembles smooth muscle
Gastrointestinal  Bile production begins in liver
Gastrointestinal  Bowel movements
Special Senses  There are taste buds all over the mouth

Nervous System  Corpus callosum
General  Crown-heel length 12 cm

General  Head circumference 10 cm

Take a quiz

-Month 3 ends-

Unit 13:  3 to 4 Months

See Snapshots

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

Play Movie

(13 weeks)
Skeletal  Teeth are growing
Respiratory  Cilia lining airways
Nervous System  Most of body sensitive to touch
General  Crown-heel length 15 cm

(14 weeks)
Movement  Girls move their jaws more than the boys do
Movement  Light touch to mouth evokes turn toward stimulus
Nervous System  4-lobed cerebral cortex
Nervous System  Cerebellum resembles adult structure
General  Crown-heel length 17 cm
General  Fat deposits in cheeks

(15 weeks)
Blood & Immune  Stem cells arrive in bone marrow
Skin  Body fat emerges throughout the body
Endocrine  Glucagon in fetal bloodstream
Gastrointestinal  Digestive enzymes
General  Crown-heel length 19.5 cm

(16 weeks)
Movement  Quickening
Skin  Fat deposits upper & lower limbs
Skeletal  Tooth enamel
Respiratory  Bronchial tree nearly complete
Special Senses  Hormonal stress response to invasive procedures
General  Crown-heel length 21 cm

Take a quiz

-Month 4 ends-

Unit 14:  4 to 5 Months

See Snapshots

Play Movie - 4 to 5 month fetus, bronchial tree

Play Movie

(17 weeks)
Special Senses  Retina has discrete layers
Nervous System  Cerebral cortex activity

(18 weeks)
Skin  Cream-like substance protects skin
Skin  Sweat glands
Endocrine  Insulin secretion
Respiratory  Speaking motion of larynx
Nervous System  Corpus callosum complete

(19 weeks)
Skin  Melanin production
Reproductive  Number of oogonia peak (at about 7 million) within fetal ovaries
Nervous System  Daily cycles in biological rhythms

(20 weeks)
Skin  All skin layers and structures
Respiratory  Surfactant production (low levels)
Special Senses  Hearing and responding to sound begins
General  Crown-heel length 28 cm
General  Head circumference 20 cm

(20 weeks - 24 weeks)
  Eyelids separate, eyes open and close

Take a quiz

-Month 5 ends-

by Diane - Group Owner on Oct. 10, 2011 at 2:44 PM

Unit 15:  5 to 6 Months

See Snapshots

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

Play Movie

(21 weeks)
Skin  Stratum corneum

(21 weeks - 22 weeks)
General  If born prematurely from this point on, survival is possible

(22 weeks)
Nervous System  Behavioral states

(23 weeks)
General  Brain weight 100 grams

(24 weeks)
Special Senses  Blink-startle response; females before males
General  Crown-heel length 34.5 cm

Take a quiz

-Month 6 ends-

Unit 16:  6 to 7 Months

See Snapshots

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

Play Movie

(25 weeks)
Gastrointestinal  Intestinal lining contains all adult
cell types
Special Senses  Rods & cones

Special Senses  The ability to taste

(26 weeks)
Skin  Additional fat deposits decrease
Skin  Tear production

Special Senses  The ability to smell has arrived

(26 weeks - 38 weeks)
Nervous System  Brain weight increases 400% to 500%

(27 weeks)
Special Senses  Pupils react to light

(28 weeks)
Special Senses  Distinguishes sounds of different
General  Crown-heel length 39.5 cm

Take a quiz

-Month 7 ends-

Unit 17:  7 to 8 Months

See Snapshots

Play Movie - 7 to 8 month fetus, behavioral states

Play Movie

(30 weeks)
Respiratory  Breathing motions are common even though
there is no air in the womb
Nervous System  6-layered cerebral cortex

General  Head circumference 30 cm

(32 weeks)
Muscular  Esophagus: Lower esophagus muscles
Renal/Urinary  Glomeruli formation complete

Respiratory  Alveoli

Nervous System  Memory - music preferences

General  Crown-heel length 45 cm

(32 weeks - 36 weeks)
Special Senses  Prenatal food affects newborn taste

Take a quiz

-Month 8 ends-

by Diane - Group Owner on Oct. 10, 2011 at 2:55 PM

Unit 18:  8 to 9 Months

See Snapshots

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

Play Movie

(34 weeks)
General  Rapid weight gain

(35 weeks)
Muscular  Firm grip
General  Amniotic fluid volume peaks

(36 weeks)
Respiratory  Surfactant production accelerates

General  Brain weight 300 grams

General  Crown-heel length 48.5 cm

Take a quiz

-Month 9 ends-

Unit 19:  9 Months to Birth

See Snapshots

Play Movie - 9 months to Birth, ready for Birth

Play Movie

(37 weeks)
Gastrointestinal  Fetus drinks an estimated 15 oz (or
450cc) of amniotic fluid/day

(38 weeks)
Respiratory  Air breathing begins

Cardiovascular  By term, the typical umbilical cord
measures 20 to 24 inches (50 to 60 cm)
Cardiovascular  Heart beats 54 million times before
Cardiovascular  Major circulatory changes

Nervous System  Spinal cord ends at third lumbar
General  Brain weight 350 grams

General  Crown-heel length 50 cm

General  Fetus initiates labor

General  Head circumference 35 cm

General  Time to be born!

Take a quiz


-Fetal Period ends and the Newborn Period begins-

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