Germinal Period Germinal period: Lasts about 14 days, from conception until implantation. Fertilization: Usually occurs in the fallopian tube when one sperm joins with the egg. Zygote: The new cell formed when the sperm and egg combine their genetic information. Mitosis: The zygote begins rapidly dividing into more cells. Blastocyst: After several days of cell division, the developing organism becomes a blastocyst. Embryonic disk: Inner group of cells that develops into the embryo. Trophoblast: Outer group of cells that helps provide support and nourishment. Implantation: The blastocyst attaches to and becomes implanted in the uterine wall. Important: Many zygotes do not survive the first two weeks because of problems with fertilization, genetic material, cell division, or implantation. The Embryonic Period Embryonic period: Begins around the third week after fertilization and lasts through the eighth week. Embryo: The developing organism after implantation. Placenta: Provides the developing embryo with oxygen and nutrients and removes waste. Umbilical cord: Connects the developing embryo/fetus to the placenta. Cell differentiation: Cells become specialized and develop into different tissues and organs. Cephalocaudal development: Development occurs from head to tail. Proximodistal development: Development occurs from the center of the body outward. Organ development: Major body structures begin forming during this stage. Heart: The early heart structure begins to pulse around the fourth week. Vulnerability: The embryonic period is especially sensitive to harmful substances (teratogens) because major organs are developing. End of embryonic period: At about 8 weeks, the embryo is approximately 1 inch long and begins responding to touch. The Fetal Period Fetal period: Begins during the ninth week and continues until birth. Growth: Major body structures continue to develop and mature. Third month: The fetus has developed its major body parts, including external genitalia. Further development: Hair, nails, teeth, and body systems continue developing throughout pregnancy.

Fertilization: Sperm and egg unite to create a zygote. Zygote: The first cell of a developing human; divides quickly. Embryonic period: Development of major organs and body parts starts. Fetal period: Fetus is growing; development of organs continues. Placenta: Provides fetus with oxygen and nutrients; waste elimination occurs. Umbilical cord: Connects fetus to the placenta; transports nutrients and oxygen. Amniotic fluid: Protects the developing fetus. First trimester: Development of body systems and organs starts. Second trimester: Fetus is growing quickly; movements are possible. Third trimester: Development of organs is continuing; weight gain occurs to prepare for birth. Prenatal care: Prenatal medical care to ensure good health of the mother and fetus. Teratogens: Substances or environmental agents that may hinder fetal development, such as alcohol, drugs, and certain infections. Nutrition: Nutrition including folic acid and iron for good development.