Notes

How Life Begins Life begins with the union of an egg from a female and a sperm from (conception), or joining of the sperm and egg, can a male. Fertilization Sexual intercourse is the repro- occur because of sexual intercourse. ductive process in which the penis is inserted into the vagina and through which a new human life may begin. During sexual inter course, the penis can deliver millions of sperm to the female

Fertilization From the vagina sperm travel through the uterus and into the fallopian tubes where fertilization normally occurs. Only a small fraction of the sperm complete the journey to the egg. How- ever, it takes only one sperm to fertilize an egg. Once a sperm penetrates the egg, a chemical change prevents other sperm from entering the egg. The genetic material of the egg and spem combine to form one cell, called a zygote. Genes play an important role in the development of a human. In fact, all of the genetic information needed to create a human is found in the zygote

The Fertilized Egg Divides The zygote travels down the woman's fallopian tube toward her uterus. The journey takes about 3 to 5 days. As the zygote moves down the fallopian tube, it divides into two cells, then into four cells, and then into a ball of many cells.

The Embryo Implants in the Uterus A developing human from fertilization through the first 8 weeks of development is called a embryo. The embryo travels from the fallopian tube into the utenus. Within 3 to 5 days, this ball of hundreds of cells becomes embedded in the uterine wall. This event is called implantation. Once implanta- tion of the embryo happens, the female is considered to be pregnant. The uterus will be the embryo's home until the baby is born.

A Placenta Supports the Baby The baby's growth in the uterus is dependent on a placenta. The placenta is a blood vessel-rich organ that forms in a mothers uterus and that provides nutrients and oxygen to and removes wastes from a developing human. Most substances, including drugs and alcohol, can pass through the placenta into the baby. If a mother eats, injects, or inhales anything harmful, her baby can be affected

How a Baby Develops process. What begins as one cell The growth of a baby is a fascinating develops into a baby made of trillions of cells over a 38 to 40 week period. Figure 6 summarizes some of the developmental changes in the growing baby.

First Trimester The first trimester, or first 3 months, is a major time of growth and change. After implantation, the embryo starts development, the heart starts growing rapidly By the fourth week beating, arm and leg buds appear, and the eyes and brain begin to develop. The embryo is less than a fourth of an inch long, or about the size of a BB pellet.
Surrounding the embryo is a thin, fluid-filled membrane called the amnion. The amnion protects the growing embryo.The umbilical cord is another new development. It connects the embryo to the placenta
The term for a developing human from the start of the ninth week of pregnancy until delivery is fetus. Brain waves can be detected and muscle movement begins in the fetus. The bones and muscles are developing. By the end of the first trimester all of the major body parts, such as the heart, brain, lungs, eyes, arms, and legs, have formed. The most critical development is complete. However, not all parts can function fully Second Trimester

The second trimester, or months 4 through 6 is a time when the organ systems continue to develop. By 4 months, the mother can feel the fetus move or "kick." The reproductive organs can be recognized as distinctly male or female By the end of this trimester, the fetus can hear and recognize voices. Hair forms on the body Head and facial features become apparent and fingers and toes grow nails. Although development is not complete, a fetus b pre maturely at the end of this trimester may be able to survive with med- ical assistance and support.

Third Trimester The third trimester, or months 7 through 9, is a time when the fetus gains most of its weight. A fetus requires a lot of nutrients from the mother. A large percent of the iron and calcium in the mother's food will be delivered to the growing fetus. By 8 months, most fetuses are about 20 inches long. The brain develops further, and all other organs are almost complete. The fetus can even grasp with his or her hands. Fat deposited underneath the skin makes the fetus's skin become very smooth. By the end of 36 weeks, the fetus is almost ready to live outside the mothers body However, the fetus nervous system will continue to develop after birth.


First trimester At 6 weeks the embryo is almost an inch long. Eyelids and ears are form- ing. Even the tip of the nose can be seen

Second trimester At 16 weeks the fetus is 5 to 6 inches ong and weighs about 5 ounces. The fetus can yawn, stretch, and even make facial expressions.

Third trimester At 32 weeks the fetus is about 20 inches long and weighs almost 5 pounds. A layer of fat has formed underneath the skin.


Early Child Development The fastest period of growth after birth takes place from birth to the age of one. By 2 months, a baby will spend several hours a day awake but mostly sleeps. Babies can raise their head at this age because of good neck control. Babies also begin smiling at faces they recognize.
At 4 months, babies are rolling from front to back, making cooing sounds, smiling and spending more time awake Their feeding sched- ules become more regular, and many babies can sleep through the night.
By 6 months, babies can sit up and have excellent head control. Most babies will crawl at 9 months and begin walking and talking by development extraordinary 1 year. The nervous system undergoes during the first year of life. independence.
Temper The "twos" are marked by social tantrums" may occur as children desire healthy independence. Toilet training often begins this year. Encouraging a healthy diet at this age can help establish future healthy eating habits.
Between 5 and 6 years, most children are ready to begin school. By this age, they are toilet trained, have well-developed speech, and are ready for more social interactions with other children.
The late childhood years from age 6 to 12 are marked by dra- matic intellectual and psychological changes. Children experience an important part of their social development in school. Children learn to read, do math, and interact with others. Parents should encourage their children to eat nutritious food, communicate their feelings, and respect all people It is important for parents to be positive role models for their children Childhood ends with the beginning of adolescence, which brings changes and responsibilities.