1. From Fertilization to Old Age…
Human Development
From Fertilization to Old Age…

2. Fertilization
Human development begins with 2 parents, each producing a sex cell, through a process called meiosis.
During meiosis, each parent produces sex cells that contain only half (23) of the chromosomes necessary to produce an offspring.
The male sex cell is called the sperm and the female sex cell is called an egg.
Fertilization is the process in which the male and female sex cells join.
The result of fertilization is the zygote, which is the first cell of the new developing offspring. This stage of development last approximately 3 weeks.

3. Cell Division & Implantation
Once the female egg is fertilized, now called a zygote, it travels through the female’s reproductive system into an area called the uterus.
Implantation is the process by which a fertilized egg (zygote) becomes implanted into the lining of the uterus of female humans (and other mammals).
The uterus is a hollow, muscular organ in the pelvic area of females. This is where the zygote will begin its developing process.
Cell Division is the process by which a cell, in this case the parent cell, divides into 2 or more cells called daughter cells. Once cell division occurs, the zygote is then called an embryo.
Female uterus during fertilization
An artist’s rendering of cell division

4. Cell Division by Mitosis (3:52)

5. Embryonic and Fetal Development
Embryo is the name given to the developing organism between weeks 3 and 8 of the mother’s pregnancy.
After 8 weeks, the developing embryo begins the first stages of fetal development. The developing organism will remain a fetus until birth.
Actual size of zygote through 8th week of embryonic development
Human embryo containing 8 cells

6. Fetal Development
Fetus after 8 weeks of development
Plastic model of 8 week old fetus
*At the 20 week period, parents can usually find out what the sex of the developing baby will be.
Fetus at 20 weeks

7. Fetal Development (cont.)
A newborn fetus is born at approximately the 40th week of “gestation” (pregnancy).
4-D image of fetus at 35 weeks
From 35 to 40 weeks a fetus is considered to be “full term.” Full term means that the fetus is fully developed and could survive outside of the mother’s uterus.

8. Infancy through Primary School Age
Infancy lasts from approximately 3-4 weeks (1 month) after birth to months of age.
The 11th to 12th month (1 year) marks the end of infancy and the beginning of toddlerhood.
At 3-4 years a child is considered a preschooler.
Ages 5-10, a child is at the primary school age level of child development.
image/svg+xml 1 2 3
Birth
Weeks
Months
Neonate/newborn
Infancy 4 6 7 8 9 10 11 5
Years
Age
Periods
Childhood
Play age
Preschooler 12 13 14 16 17 18 19 15
Primary school age
Preteen
Puberty (girls)
Puberty (boys)
Adolescence
Preadolescence
Adulthood 20 22 23 24 26 27 28 29 25 21
Secondary school age
Child development periods
Toddlerhood
= Definitions differ in faded interval
= Change in time scale
Toddler
Primary school age
Infant

9. Pre-Adolescence (sound familiar?)
Pre-adolescence begins towards the end of primary school age.
Pre-adolescence begins at approximately age 10 and leads into a stage of development called puberty which marks the beginning of adolescence.
Puberty is a stage of development that occurs at different times for boys and girls. Puberty is the point at which a child’s body begins changing into an adult’s body that is capable of reproduction.
Usually, girls start puberty before boys do. At ages girls are beginning this process while boys generally wait until the ages of Puberty also marks the beginning of adolescence. Adolescence lasts from the beginning of puberty into adulthood.
Pre-adolescent
Adolescent

10. Adulthood and Old Age
Adulthood begins at the conclusion of puberty. It is the period of human development where physical growth (growing up) has stopped and a person is fully developed.
Old-age is the period in which a human is reaching or has reached the expected life span of human beings. Life span also differs for men and women.
Old age
adults