Development Before Birth Chapter 13, Lesson 2 Glencoe Text Pages 515-521

Science Content Standards 5e. Students know the function of the umbilicus and placenta during pregnancy Chapter 13, Lesson 2 Main idea: The normal development of a fetus depends on the good health of its mother Definition - Fetus:: a developing human from usually two months after conception to birth

Real World Reading Connection Did you know that someone might have taken your picture before you were born? A sonogram uses sound waves to produce a video image of a fetus. It can help a medical provider determine if the fetus is developing normally and whether it is a girl or boy.

Fetal Development Sexually produced organisms began life as a zygote that forms when a sperm fertilizes and egg (chapter 3). Cell division of a human zygote begins about 24 hours after fertilization. Cells continue to divide -after about 7 days a hollow ball of more than 100 cells has formed called a blastula. This ball of cells implants itself into the endometrium (lining of uterus). After 2 weeks of growth, cells begin to arrange themselves into 3 layers. Different body structures eventually form from each layer. Over 9 months, a human embryo develops into a baby.

Human sex cells (not drawn to the same scale)

Growth and Development of Body Systems (p. 516) The development of a baby within a female’s uterus is called pregnancy. In humans, pregnancy usually lasts for about 40 weeks (after the last menstruation cycle). The nine months are divided into 3 parts called trimesters. By the end of the first trimester, an embryo has all the structures that will become the major organ systems During the second trimester, an embryo is called a fetus which changes as it continues to develop. The pregnant female can feel the fetus' movements. During the third trimester, the fetus grows rapidly, nearly tripling in size in preparation for birth. First trimester: 0 - 12 weeks (0 - 3 and a half months) Second trimester: 12 - 24 wks (3 1/2 months to 6 mths) Third trimester: 24 - 40 weeks (7 months to delivery)

Premature Babies Sometimes, infants are born prematurely, before development is complete. By definition, premature is any baby born before 37 weeks of gestation. Premature babies can have difficulty surviving because some of their organs are not ready to function. The lungs are among the last organs to develop fully. Premature babies must often be cared for in the hospital until their lungs fully develop. Premature babies usually have low birth weights which can lead to physical challenges, learning difficulties, or behavioral problems as they grow older.

Placenta & Umbilical Cord Nutrients and oxygen move from the mother’s blood into the placenta, through the umbilical cord, and then to the fetus. Wastes from the fetus move through the umbilical cord, to the placenta, and then to the mother’s blood.

Placenta & Umbilical Cord (p. 517) During development, a growing fetus receives oxygen and nutrients from its mother. A pregnant women receives carbon dioxide and wastes from her fetus. This exchange of materials takes place through a disc shaped organ called the placenta. A placenta begins to form when an embryo first implants itself into the lining of the uterus (Endometrium). The placenta contains many blood vessels from both the fetus and endometrium, but they are not directly connected. Substances enter and leave the body of a fetus through an umbilical cord. The umbilical cord contains 2 arteries and one vein that connect the fetus to the placenta. When a baby is born, its umbilical cord is cut, but a few inches remain attached to the baby’s body. After a few days, it dries up and drops off. The place the umbilical cord was attached to the body is called the navel, or belly button.

Fetal Health (p. 518) Everything that happens in a women’s body has an effects on her developing fetus. Anything that she does that could harm her own health before or during the pregnancy could also harm the fetus. It is important that pregnant women take care of their health before and during their pregnancy which is called Prenatal Care (includes advice, information about nutrition, infections, and substances that can harm a baby (some foods, liquids, medicines, etc…) Research shows that a pregnant women who receives prenatal care by a health provider has a better chance of delivering a healthy baby.

Nutrition (p. 518) All the energy and nutrients a fetus needs for normal development must come from the mother. Vitamins, minerals, proteins, fat, and carbohydrates pass from mother to fetus through the placenta. Doctors often recommend vitamin supplements. A pregnant women needs to eat a healthy diet and is usually advised to add about 300 more calories a day to her diet. The added calories supply the extra energy needed for the development of the fetus. A pregnant women should avoid caffeine which can increase a women’s blood pressure and heart rate, which can be stressful to her fetus.

Environmental Factors (p. 519) A pregnant women can encounter harmful substances in her environment that can present health risks for her fetus. A pregnant women is advised to stay away from: Chemicals (often found in cleaning supplies) Pesticides and insect repellents Lead (found in electronics, paint, and air pollution) Cigarette smoke (even second hand) Alcohol (cause FAS) Fetal Alcohol Syndrome) Harmful substances can reduce the amount of nutrients to the fetus, cause premature birth, birth defects, low birth weights, or miscarriage (loss of embryo during the first trimester).

Viruses (p. 520) Viruses can pass from a pregnant women to her fetus through the placenta or during childbirth. Nearly everyone has had an infection caused by a virus. You’ve probably had colds, flu, or chicken pox. Some viruses do not cause harm to adults, but can be very harmful (birth defects or even death) to a fetus or newborn. Other viral infections include genital herpes and HIV/AIDS. HIV/AIDS attacks the bodies immune system limiting a infected persons ability to fight infection. One out of every 4 pregnant women with HIV (human immunodeficiency virus) pass the HIV onto their fetus.