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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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 %