1. 9 months from zygote to little baby
Human Development
9 months from zygote to little baby

2. Human Development – Process
Cleavage
Morphogenesis
Organogenesis
(Differentiation)
Growth
Cells Divide
Cells Move
Cells Specialize
Cells Divide

3. Human Development - Stages
Zygote
Single cell
cleavage
Morula
Solid ball of cells
Blastula
Hollow ball of cells
Gastrula
3 layers
morphogenesis
Embryo
Head and tail
organogenesis
Fetus
Looks human
growth

4. Human Development - Timeline
Zygote
30 hours
Morula
30 hr –Day 4
Blastula
Day 4-7
Gastrula
Day 7 – Week 3
Embryo
Weeks 3 – 8
Fetus
Weeks 8 – 40

5. Cleavage Period of rapid cell division
Begins in fallopian tube and continues as fertilized egg proceeds to uterus
Cell divisions produce a solid ball of cells (morula) and then a fluid-filled ball (blastula or blastocyst)

6. Implantation Blastula/blastocyst implants into uterine wall
Day 5 – Day 7
Inner cell mass – cells inside ball – will become baby
Trophoblast – cells around ball – will become placenta

7. Gastrula
Once inside uterine wall, cell movement – morphogenesis - begins
Movement creates three distinct cell layers (also called germ layers)
Endoderm = inner layer becomes lungs, blood vessels. digestive system
Ectoderm = outer layer becomes nervous system, skin, sense organs
Mesoderm = middle layer becomes muscle, bone, heart, blood

8. Gastrula + Embryonic Membranes
Human embryos have membranes evolved from shelled egg reptiles
Chorion – surrounds entire structure (placenta + embryo)
Amnion – surrounds embryo
Yolk sac – holds food/nutrients
Allantois – holds waste

9. Embryo + Organogenesis
Cells continue to move and begin to specialize as specific tissues/organs
Embryo begins to develop head/tail shape and specific organs
Yolk sac provides nutrients and allantois collects waste as placenta becomes functional

10. Fetus + Growth All organs are formed by end of week 8
Developing baby looks human and is now called a fetus
From this point forward, organs grow by adding cells

11. Placenta
Specialized mammalian structure develops from embryonic membranes
Chorion membrane invades uterine wall producing projections called chorionic villi
Villi contain baby’s blood vessels and grow into pools of maternal blood

12. Placenta Chorion membrane separates baby’s blood from mother’s blood
Mother’s blood provides nutrients and oxygen to baby’s blood
Baby’s blood provides wastes – CO2 and urea – to mother’s blood
Substances move – by diffusion – from high concentration to low concentration
Placenta works from week 3-4 and is fully functional by week 12

13. Organogenesis – Gender Development
Both genders have a primordial gonad
Both genders have two sets of tubes – Mullerian and Wolffian ducts
Primordial gonad  ovary or testes
Wolffian duct  male genitalia
Mullerian duct  female genitalia

14. Organogenesis – Gender Development
Male development occurs at 5-6 weeks
Primordial Gonad
Testes
Testosterone
Wolffian Duct
Vas Deferens
Scrotum
Penis
SRY protein from Y chromosome

15. Organogenesis – Gender Development
Female development – occurs at 8 weeks
Primordial gonad
Ovary
Estrogen
Mullerian ducts
Fallopian tubes
Vagina
Uterus

16. Secondary Characteristics
Gender Development
Male
Female XY
Genetics XX
testosterone
estrogen
Hormones
Estrogen
 Testosterone
Sperm
Gametes
Egg/Ova
Testes
Penis
Organs
Ovary
Uterus
Vagina
Body/Facial Hair
Muscle Development
Deep Voice
Secondary Characteristics
Breasts
Wider Hips
Higher Body Fat %