The Life Cycle Chapter 17 & 18

Prenatal Development The human body begins as one microscopic cell that is formed by the union of a male sperm cell and a female egg cell; fertilization This is also known as conception The cell that is formed after fertilization is a zygote

Prenatal Development Implantation - process by which the zygote attaches to the uterine wall Embryo - cluster of cells that develops between the third and eighth week of pregnancy The group of developing cells is the fetus

The Growing Embryo The cells of the embryo continue to grow and divide, forming three layers that develop into various body systems. One layer becomes the respiratory and digestive systems. A second becomes muscles, bones, blood vessels, and skin. The third develops into the nervous system, sense organs, and mouth.

The Growing Embryo Two important structures form outside the 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 The placenta is thick, blood-rich tissue that lines the uterus during pregnancy and nourishes the embryo

The Growing Embryo During pregnancy, blood supply of the mother and embryo are kept separate Oxygen and nutrients are passed from the mother’s blood to the embryo, and waste from the embryo is passed to the mother’s blood Waste is then excreted from the mother’s body along with her own body wastes

Stages of Development - First Trimester 0 - 2 weeks: Zygote floats freely in the uterus before implanting Spinal cord grows Brain, ears, and arms begin to form Heart starts beating 3 - 8 weeks: About 1 inch long at 8 weeks Mouth, nostrils, eyelids, hands, and feet form Nervous and cardiovascular systems are functional 9 - 14 weeks: Fetus develops a human profile Sex organs, fingernails, and toenails develop By week 12, it can make crying motions and may suck its thumb

First Trimester

Stages of Development - Second Trimester 15 - 20 weeks: Fetus can blink on its own and becomes more active Body begins to grow; head growth slows and limbs reach full proportion Eyebrows and eyelashes develop 21 - 28 weeks: Fetus can hear conversations and has a regular sleep cycle Weight increases rapidly; fetus is about 12 inches long, weighing 1lb. If born after 24 weeks, the fetus may survive but will need special care

Second Trimester

Stages of Development - Third Trimester 29 - 40 weeks: Fetus uses all five senses and begins to pass water through the bladder Some dream during sleep cycles About 266 days after conception, the baby weighs 6-9 lbs. and is ready for birth

Third Trimester

Multiple Births In most cases, fertilization results in one embryo Twins, triplets, and quadruplets can result when multiple embryos are formed Identical twins result from a single zygote that splits into two separate embryos with identical traits Fraternal twins occur when two eggs are released and fertilized

A Healthy Pregnancy Prenatal care refers to the steps that a pregnant female can take to provide for her own health and the baby’s health. Calcium helps build strong bones and teeth, as well as healthy nerves, muscles, and heart rhythm Protein helps form muscle and other tissue Iron makes red blood cells and supplies oxygen to cells Vitamin A helps in the growth of cells, bones, and eyes Vitamin B Complex aids in forming the nervous system Folic acid helps develop the central nervous system

A Healthy Pregnancy Avoid tobacco use 30% of low birth weight, 14% of premature births, 10% of infant deaths Avoid alcohol use Alcohol consumed by the mother passes to the baby through the umbilical cord; the baby breaks down alcohol slower than the mother Fetal Alcohol Syndrome is a group of alcohol-related birth defects FAS leads to problems with learning, memory, and attention problems, as well as visual and hearing impairments Avoid drug use Lead to respiratory and cardiovascular problems, mental impairments, and birth defects Babies can be born addicted to the drugs

Fetal Alcohol Syndrome Living with FAS

Environmental Hazards Avoid hazards in the environment Lead - miscarriages, low birth weight, mental disabilities, behavior issues Mercury - found in certain types of fish Smog - birth defects, low birth weight, premature birth, stillborn, death Greatest period of risk is during the second month of pregnancy when the organs are developing Radiation - Found in x-rays, can affects growth and cause mental issues

Complications of Pregnancy Roughly 70% of births occur through vaginal delivery Complications can result in a premature birth Takes place at least three weeks before the due date Serious complications may also lead to miscarriage Spontaneous expulsion of a fetus occurring before the twentieth week of pregnancy The delivery of a fetus that has died after the twentieth week of pregnancy is called a stillbirth

Complications of Pregnancy Gestational hypertension - high blood pressure during pregnancy May occur after the twentieth week of pregnancy Pre-eclampsia - a severe form of hypertension Can prevent the placenta from getting enough blood to nourish the fetus Ectopic pregnancy - zygote implants not in the uterus but in the fallopian tube, abdomen, ovary, or cervix Impossible for the fetus to receive nourishment #1 cause of death for women in the first trimester

Childbirth Step 1: Labor Muscle contractions of the uterus become regular, stronger, and closer together Cervix dilates Step 2: Delivery Cervix is fully dilated; baby passes through birth canal Baby takes its first breath and cries to clear the lungs Step 3: Afterbirth Placenta is still attached by to the baby by the umbilical cord; contractions continue

Heredity and Genetics Heredity is the passing of physical traits from parents to their children. Cells in the body contain a nucleus; inside the nucleus is a set of chromosomes Thread-like structures that carry codes for inherited traits Sections of chromosomes called genes are the basic units of heredity The chemical unit that makes up chromosomes is called DNA

Genetics and Fetal Development Most humans have 46 chromosomes, or 23 pairs Egg and sperm cells each have half that, 23 chromosomes When egg and sperm cells unite during fertilization, the resulting zygote will have 46 chromosomes 23 from the mother 23 from the father These chromosomes carry heredity traits of the parents, which are passed on to the child

Dominant vs. Recessive Genes Appear when present Recessive Only appear when dominant gene is not present

Genetic Disorders A person can inherit genes that contain a mutation, or an abnormality Gene mutations may result in birth defects or increase the likelihood of developing a disease These diseases, called genetic disorders, are disorders caused partly or completely by a defect in genes Most cannot be cured, but can be treated Gene therapy is the process of inserting normal genes into human cells to correct genetic disorders

Genetic Disorders Amniocentesis is a procedure in which a syringe is inserted through a pregnant females abdominal wall to remove a sample of amniotic fluid for testing 16-20 weeks after fertilization Chorionic villi sampling is a procedure in which a small piece of membrane is removed from the chorion, a layer of tissue that develops into the placenta Around the 8th week of fetal development

The Life Cycle Continues Adolescence is the period between childhood and adulthood Puberty is the time when a person begins to develop certain traits of adults of his or her gender

Secondary Sex Characteristics In females Breast development Waistline narrows, hips widen Body fat increases Menstruation starts In males Facial hair appears Voice deepens Shoulders broaden Muscles develop Hairline begins to recede In both Body hair appears; perspiration increases Permanent teeth grow in

Brain Development in Adolescents Cognition is the ability to reason and think out abstract solutions; they now have the ability to: anticipate consequences of a particular action think logically understand different points of view

Brain Development in Adolescents Cerebellum - coordinates muscle movement, involved in the coordination of the thinking process Frontal cortex - responsible for planning, strategizing, impulse control, and reasoning Amygdala - associated with emotion, teens use this more than adults Corpus callosum - connects the two sides of the brain, involved in creativity and problem solving