Chapter 17 The Beginning of the Life Cycle

1. Chapter 17The Beginning of the Life Cycle

2. As a fetus develops during pregnancy, special care needs to be taken to ensure the fetus and mother remain healthy.

3. The Very Beginning A single cell, formed from one egg and one sperm, can grow into a complex human being.

4. The Very Beginning The human body begins as one microscopic cell that is formed by fertilization, also known as conception. Fertilization The union of a male sperm cell and a female egg cell

5. The Very Beginning • The cell that results from fertilization is called a zygote. • The zygote begins to divide and travel through the fallopian tube.

6. The Very Beginning Within a few days, implantation occurs. Implantation The process by which the zygote attaches to the uterine wall

7. The Very Beginning After about two weeks, the zygote becomes an embryo. Embryo A cluster of cells that develops between the third and eighth week of pregnancy

8. The Very Beginning The embryo is called a fetus after about eight weeks. Fetus Group of developing cells

9. The Growing Embryo Eventually, the embryo forms three layers of tissue. One layer becomes the respiratory and digestive systems. A second layer develops into muscles, bones, blood vessels, and skin. The third layer forms the nervous system, sense organs, and mouth.

10. The Growing Embryo • The amniotic sac is a thin, fluid-filled membrane that surrounds and protects the developing embryo. • The umbilical cord is a ropelike structure that connects the fetus with the mother’s placenta.

11. The Growing Embryo The placenta is thick, blood-rich tissue that lines the walls of the uterus during pregnancy and nourishes the embryo.

12. The Very Beginning

13. The Growing Embryo

14. The Growing Embryo

15. The Growing Embryo

16. The Growing Embryo

17. Multiple Births • In most cases, fertilization results in one embryo. • Twins, triplets, and quadruplets, known as multiple births, can result when multiple embryos are formed.

18. Identical traits and the same gender. Single zygote that splits into two separate embryos. Two eggs are released and are fertilized by two different sperm. Can be different genders. Multiple Births Identical Twins Fraternal Twins

19. A Healthy Pregnancy A pregnant female can maintain the health of her fetus in many different ways. Seeing a doctor regularly throughout the pregnancy will provide a new mother with the care and nutritional advice she needs.

20. A Healthy Pregnancy A pregnant woman needs prenatal care to ensure her health and that of her growing baby. Prenatal care The steps that a pregnant female can take to provide for her own health and the health of her baby

21. What to Eat While Pregnant • Pregnant females are encouraged to take prenatal vitamins to provide a balance of nutrients.

22. What to Eat While Pregnant Calciumhelps build bones and teeth, nerves, muscles, and heart. Proteinhelps form muscle and other tissue. Ironmakes red blood cells and supplies oxygen to cells. Vitamin Ahelps in the growth of cells and bones and in eye development. Vitamin B complexaids in forming the nervous system. Folic acidis critical in development of central nervous system.

23. What to Eat While Pregnant Females at a healthy weight before becoming pregnant can gain between 25 and 35 pounds during pregnancy.

24. A Healthy Fetus Expectant mothers should avoid tobacco, alcohol, drugs, and environmental hazards. An expectant mother should avoid substances that can harm her and her fetus.

25. Avoid Tobacco Use • Exposure to secondhand smoke increases the risk of having a low-birth-weight baby. • Smoking may also affect growth, mental development, and behavior after a child is born.

26. Avoid Alcohol Use Fetal alcohol syndrome can cause learning, memory, and attention problems, as well as visual and hearing impairments. Fetal alcohol syndrome A group of alcohol-related birth defects that includes both physical and mental problems

27. Avoid Drug Use Prescription or over-the-counter medications should be used only with the approval of a doctor or other health care professional. In some cases, drug use may lead to the premature birth of the infant, or even a miscarriage.

28. Avoid Hazards in the Environment A pregnant female should avoid these common hazardous substances in the environment. Lead Mercury Smog Radiation

29. Avoid Hazards in the Environment Activities such as painting or using lead-based products should be avoided or done carefully during pregnancy.

30. Complications of Pregnancy A pregnancy may have an unexpected outcome. Most pregnancies result in the birth of a healthy baby.

31. Complications of Pregnancy The complications of pregnancy can result in • a cesarean delivery, made through an incision in the mother’s abdomen. • premature birth, at least three weeks before the due date. • miscarriage, the spontaneous expulsion of a fetus before the twentieth week of pregnancy.

32. Complications of Pregnancy Gestational hypertension, or high blood pressure during pregnancy, may occur after the twentieth week of pregnancy. A severe form of this is preeclampsia.

33. Complications of Pregnancy An ectopic pregnancy results when a zygote implants not in the uterus but in the fallopian tube, abdomen, ovary, or cervix. This makes it impossible for the fetus to receive nourishment and grow.

34. Childbirth The birth of a baby takes place in three steps: labor, delivery, and afterbirth. Expectant parents must decide where the birth will occur.

35. Childbirth Birth occurs in three steps. Step 1: Labor Step 2: Delivery Step 3: Afterbirth

36. Childbirth Step 1: Labor.Muscle contractions of the uterus become regular, stronger, and closer together. This causes the cervix— the opening to the uterus—to dilate, or widen.

37. Childbirth Step 2: Delivery.Once the cervix is fully dilated, the baby passes through the birth canal and emerges from the mother’s body. The baby takes its first breath and cries to clear its lungs of amniotic fluid.

38. Childbirth Step 3: Afterbirth.The placenta is still attached to the baby by the umbilical cord. Contractions, although weaker, will continue until the placenta (now called the afterbirth) is pushed from the mother’s body.