FETAL DEVELOPMENT

THE FIRST ELEVEN DAYS OF HUMAN DEVELOPMENT

Ovum and Sperm

First Cell Divison

Blastocyst showing inner cell mass

Trophectoderm (will become placenta)

Inner cell mass (will become baby)

Trophectoderm

Inner cell mass

Zona pellucida

Blastocyst

Cell Differentiation

By the end of the first week, cell differentiation occurs to create two tissue types:

Ectoderm – forms outer skin, sensory organs, entire brain and nervous systemEndoderm – forms the internal organs (gut, lungs, liver, glands

By the end of the second week, the third cell type differentiation occurs

Mesoderm – forms the bones, muscles, connective tissues, circulatory system, and smooth muscles of the digestive system

Spinal Cord and Nervous System Formation

Neurogenesis starts in the third week after fertilization, creating neurons at a rate of over 250,000 per minute

The synapses for each neuron are created – up to 15,000 synapses per neuron – at a rate of 1.8 million synapses per second between 8 weeks gestation and 2 years after birth

By 9 weeks the spinal cord is formed and starting to function

Brain

Eye

Heart

Liver

Arm bud

Leg bud

Umbilicalcord

Placenta

Yolk sac

Embryo at 5 weeks from conception

6 week old embryo in sac

Embryo at 6 weeks after conception

Heart

Eye

Arm bud

Leg bud

Umbilical cord

Embryo in sac at 8 weeks after conception

Hemispheres of brain

Placenta

Close-up of hands at 10 weeks LMP

Fetus at 12 weeks

Hand at 12 weeks

Fetus at 3+ months

Ear at 3+ months

Fetus at 15 weeks

Fetus at 15 weeks

Foot at 16 weeks

Sucking thumb at 18 weeks

Female fetus at 18 weeks

Ear at 5 months

Fetus at 5 months

Fetus at 24 weeks

Fetus at 7 months

Fetus at 36 weeks

Full term baby at 39 weeks, after “finishing touches”