http://www.ck12.org Chapter 1. Human Biology
Childbirth
Duringchildbirth, a baby passes from the uterus, through the vagina, and out of the mother’s body. Childbirth
usually starts when the amniotic sac breaks.
Then, the muscles of the uterus start contracting. The contractions get stronger and closer together. They may go
on for hours. Eventually, the contractions squeeze the baby out of the uterus. Once the baby enters the vagina, the
mother starts pushing. She soon pushes the baby through the vagina and out of her body.
As soon as the baby is born, the umbilical cord is cut. After the cord is cut, the baby can no longer get rid of carbon
dioxide through the cord and placenta. As a result, carbon dioxide builds up in the baby’s blood. This triggers the
baby to start breathing. The amniotic sac and placenta pass through the vagina and out of the body shortly after the
birth of the baby.
Vocabulary
- amniotic sac: Fluid-filled membrane that surrounds the fetus.
- childbirth: Passage of the baby from the uterus, through the vagina, and out of the mother’s body.
- embryo: Stage of development that occurs from implantation in the uterus through the eighth week after
fertilization in humans. - fetus: Developing human baby at least eight weeks after fertilization.
- placenta: Mass of maternal and fetal blood vessels where the the mother’s and fetus’s blood exchange
substances. - umbilical cord: Tube that connects the fetus to the placenta.
Summary
- A zygote develops into an embryo and then a fetus.
- During pregnancy, the amniotic sac, placenta, and umbilical cord develop inside the mother’s uterus.
Practice
Use the resource below to answer the questions that follow.
- Anatomy of Childbirthat http://www.pbs.org/wgbh/nova/body/anatomy-childbirth.html
- What hormone does the mother secrete at the start of labor? What is the affect of this hormone
- What signals the start of "active labor"?
- What happens at the "pushing stage" of childbirth?
- What is the leading cause of maternal death in developing countries?
Review
- Explain the role of the amniotic sac and placenta during fetal development.
- What is the difference between an embryo and a fetus?