The Beginning of the Life Cycle Chapter 17 The Beginning of the Life Cycle

Lesson 1 The developing fetus and the mother need special care during pregnancy to ensure the health of the baby and mother. The life cycle starts with fertilization, aka conception. Fertilization – the union of a male sperm cell and a female egg. The cell that results is called a zygote.

Lesson 1 Continued The very beginning: Only one sperm can fertilize an egg As the zygote travels down the fallopian tube toward the uterus, it divides many times About 6 days after fertilization, the zygote burrows into the lining of the uterus Implantation – process by which the zygote attaches to the uterine wall After about two weeks the zygote becomes an embryo. Embryo – cluster of cells that develops between the third and eighth week of pregnancy

Lesson 1 Continued The embryo becomes a fetus after about eight weeks. Fetus – group of developing cells The embryo forms three layers of tissue: One layer becomes the respiratory and digestive systems A second layer develops into muscles, bones, and blood vessels A third layer forms the nervous system, sense organs, skin, and mouth

Lesson 1 Continued 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. The placenta is thick, blood-rich tissue that lines the walls of the uterus and nourishes the embryo.

Lesson 1 Continued The growing embryo: 0-2 weeks – spinal cord grows, brain, ears, and arms begin to from, heart begins to beat 3-8 weeks – 1 inch long at 8 weeks – mouth, nostrils, eyelids, hands, fingers, feet, and toes begin to form, nervous and cardiovascular system are functional 9-14 weeks – develops a human profile, sex organs, eyelids, fingernails, and toenails develop, by week 12 can make crying motions and may suck its thumb

Lesson 1 Continued 15-20 weeks – blink its eyes, more active, body begins to grow, growth of the head slows and limbs reach full proportion, eyebrows and eyelashes develop 21-28 weeks – can hear conversations, regular cycle of waking and sleeping, weight increases rapidly, 12 inches long and weighs a little more than a pound, may survive if born after 24 weeks with special medical care 29-40 weeks – uses all five senses, passes water from the bladder, some dream during the eighth and ninth months, 266 days after conception the baby weighs 6.9 pounds and is ready to be born

Lesson 1 Continued Multiple births: Identical twins – single zygote splits into two separate embryos; identical traits and the same gender Fraternal twins – two eggs are released and are fertilized by two different sperm; can be different genders Prenatal care – steps that a pregnant female can take to provide for her own health and the health of her baby

Lesson 1 Continued Females at a healthy weight before becoming pregnant can gain between 25 and 35 pounds during pregnancy. Expectant mothers should avoid tobacco, alcohol, drugs, and environmental hazards. Fetal alcohol syndrome – group of alcohol-related birth defects that includes both mental and physical problems

Lesson 1 Continued Complications of pregnancy: Cesarean delivery Premature birth Miscarriage – before twentieth week Gestational hypertension – high blood pressure may occur after the twentieth week; a severe form is preeclampsia Ectopic pregnancy – zygote implants in the fallopian tube, abdomen, ovary, or cervix

Lesson 1 Continued Childbirth: Labor – muscle contractions in the uterus become regular and stronger this cause the cervix to dilate and widen Delivery – cervix is fully dilated, baby passes from through the birth canal and emerges from the mother’s body Afterbirth – contractions will continue until the placenta is pushed from the mother’s body

Lesson 2 Certain traits, such as eye and hair color, come from both parents. Heredity is the passing of physical traits from parents to their children. Chromosomes – thread-like structures found within the nucleus of a cell that carry the codes for inherited traits Genes – basic units of heredity DNA – chemical unit that makes up chromosomes

Lesson 2 Continued Human cells contain 46 chromosomes, or 23 pairs. Egg and sperm cells have half that number – 23 chromosomes. Egg – 23 + Sperm – 23 = Zygote – 46 chromosomes. Some genes are dominant and some are recessive. Females have only X chromosomes therefore egg cells only have an X chromosome. Sperm contain either an X or a Y chromosome, thus the sperm from the male determine the gender of the child.

Lesson 2 Continued Genetic disorders are caused by defects in genes. Amniocentesis – procedure in which some of the amniotic fluid is removed and tested for genetic disorders Common genetic disorders: Sickle cell anemia – red blood cells have a sickle shape and clump together Tay-Sachs disease – destruction of the nervous system Cystic fibrosis – mucus clogs many organs Down syndrome – varying degrees of mental retardation Hemophilia – failure of blood to clot

Lesson 2 Continued Chorionic villi sampling – another method used to test for genetic disorders Gene therapy – process of inserting normal genes into human cells to correct genetic disorders

Lesson 3 Developmental tasks – events that need to happen in order for a person to continue growing toward becoming a healthy, mature adult Childhood: Birth to 12 months: Opens and closes hands Associates sounds with objects Imitates new word sounds May walk a few steps Experiences the five basic emotions Forms strong attachment to parents Begins to smile Wants companionship Begins experiencing stranger anxiety Shows strong likes and dislikes

Lesson 3 Continued Early childhood: Ages 1-3 Walks well Picks up objects Throws ball overhead Draws recognizable pictures Shows defiance and disagreement Behaves affectionately Wants to help Begins to be bothered by fears Desires approval Bosses other children Takes part in group activities

Lesson 3 Continued Middle childhood: Ages 4-6: Dresses and undresses Uses eating utensils Becomes more independent Eager to explore Craves praise and approval Self-confidence grows Begins forming friendships Becomes more outgoing and talkative Respects others’ belongings May want to things their way

Lesson 3 Continued Late childhood: Ages 7-12: Puberty may begin Sensitivity about body image may begin Sense of self Recognizes unique personality traits Sense of competence Becomes aware of the dangers in the world Deeper friendships develop Relationships with parents change Begins facing moral decisions Peer pressure becomes stronger

Lesson 3 Continued Autonomy – confidence that a person can control his or her own body, impulses, and environment Children need many different types of health screenings to make sure they do not fall behind because of something that could slow their development. Hearing Vision