1. The Life Cycle
Chapter 17 & 18

2. 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

3. 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

4. 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.

5. 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

6. 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

7. 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
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

8. First Trimester

9. Stages of Development - Second Trimester
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
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

10. Second Trimester

11. Stages of Development - Third Trimester
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

12. Third Trimester

13. 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

14. 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

15. 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

16. Fetal Alcohol Syndrome
Living with FAS

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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