Fertilization and Development
Fertilization The union of sperm and ovum – –Forms a zygote The ovum completes meiosis II following fertilization After fertilization, chemical reactions occur preventing additional sperm from entering the ovum
Early Development A fertilized egg is a zygote The zygote divides (mitosis) to become a morula (solid ball of cells) The morula hollows out to become a blastocyst The inner cell mass undergoes gastrulation to form a tube with three layers –The developing embryo is now called a gastrula c Morula Inner cell mass
Early Development Implantation of the blastocyst into the uterine wall
Primary Germ Layers Layers are formed by differentiation of cells Ectoderm (outside) –Skin –Brain and spinal cord Mesoderm (middle) –Muscle –Bones –Blood Endoderm (inside) –Lungs –Digestive tract –Liver
Multiples
Twins Dizygotic = Two zygotes –Two sperm fertilized two separate eggs –Occurs when 2 oocytes are ovulated –These twins are as alike as any other siblings Monozygotic = One zygote –Genetically identical –3 different types depending on where the split occurs
3 Types of Monozygotic Twins
From Embryo to Fetus At 3-4wks the neural tube forms –The neural tube will form the brain and spinal cord –All other organs organize around the neural tube At 8 weeks, the embryo becomes a fetus –All of the rudimentary features are formed
Life’s Greatest Miracle