The four stages will be described below briefly to help you understand what the basic of the human life cycle are.
Infancy- From the age of being a newborn to the age of two years, you were an infant. Changes you may have experienced were more coordination and teeth growing rapidly. The body was also quite out of proportion . These were all part of the infancy stage.
Childhood- Childhood lasts from the age of two years to adolescence. Your bones and teeth were growing rapidly and soon changes such as teeth being replaced with permanents happen. You also develop your intellectual skills (ABC's, reading/writing) and pretty much you have quite changed from being an infant.
Adolescence- Adolescence is the age where the body becomes sexually mature. Changes you may be going through are acne, increased growth and deeper voice. Girls also gain extra weight during this time. It is sometimes a emotionally distressing time for teenagers.
Adulthood- Adulthood is the age where the body slowly slows down. Certain changes such as hair falling out and physical activity decreasing are normal as you age . If you are over forty, you are considered a older adult. This however doesn't stop someone from doing the things they enjoy.
16.4 Femal Hormone Level
Although we tend to think of hormones kicking in at puberty, they affect our bodies even during early childhood. At puberty, hormones will begin to make major, lasting changes to a girl's body. Her breasts will get bigger and take on the shape of an adult woman's breasts. She will develop underarm and pubic hair and will get noticeably taller as a significant growth spurt occurs. Eventually her periods will start, usually as the growth spurt is beginning to slow down. Female sex hormonesThe most important hormones made by the ovaries are known as female sex hormones (sex steroids) and the two main ones are oestrogen and progesterone. If the egg released from the ovary is fertilised and a pregnancy results, a woman's hormones change dramatically. The usual fall in oestrogen and progesterone at the end of the menstrual cycle doesn't occur, so no period is seen. After childbirth, what then? Levels of oestrogen, progesterone and other hormones fall sharply, causing a number of physical changes. The womb shrinks back to its non-pregnant size, pelvic floor muscle tone improves and the volume of blood circulating round the body returns to normal. The next significant hormonal change for most women occurs around the time of the last period - the menopause. Over three to five years leading up to a woman's last period, the normal functioning of her ovaries begins to deteriorate. This can cause her menstrual cycle to become shorter or longer, and sometimes it becomes quite erratic. Periods may become heavier or lighter. Eventually, the ovaries produce so little oestrogen that the lining of the womb fails to thicken up and so periods stop altogether.
16.5 Control Of Reproduction
There are several types of control now such as birth control pill, diaphragm, and condom. Also assistantce in trying to have a baby, invitro fertilization, and GIFT.
16.6 Sexualy Transmitted Diseases
transmitted via kissing, use of an IV drug needle after its use by an infected person, as well as through childbirth or breastfeeding. Sexually transmitted infections have been well known for hundreds of years. CHAPTER 17
Fertilization constitutes the penetration of the oocyte which the sperm performs, fusion of the sperm and oocyte, succeeded by fusion of their genetic material.
17.2 Pre-Embryonic an Embryonic Development
Fertilization occurs about 24 hours before the egg is laid. A sperm cell, actually a number of sperm cells, penetrates the blastodisc on the yolk, and a new life begins. When the egg is laid, the blastoderm contains several hundred cells. When the egg cools, embryonic development stops. Embryonic development starts again when the temperature is increased. If the temperature is then decreased to room temperature a second time, the embryo will die.
Prior to incubation, all cells in the embryo look the same and have the same function. That changes, however, during the first 4 days of incubation. As cell division continues, the cells receive messages that cause them to become different types of tissues and organs. Some cells will develop into the circulatory system, others into the brain, and still others into muscles. The process in which similar cells are instructed to take on different functions is called differentiation. The first 4 days are a time of dramatic change. Mistakes sometimes occur in this process. If it is a serious mistake, the defect is lethal and the embryo dies. In the incubation process, these mistakes cause "early deads." If the biological mistake is not as serious, the embryo may develop longer before dying, or it may survive with a congenital defect.
While the embryo is developing, temporary structures are formed to support life. They are called extra-embryonic, because they do not become a part of the embryo. The one that is visible at the earliest stage of development is the amnion. It looks like a small pool in which the embryo is floating. Its purpose is to protect the embryo. The allantois is a structure that collects the waste that the embryo produces before it hatches. Many of the nutrients that the embryo needs are removed from the yolk by the yolk sac. Its blood vessels can carry nutrients from the yolk to the embryo. 
The last structure is the chorion, which lies between the embryo and the shell. An important function is for it to exchange the carbon dioxide produced by the embryo and bring oxygen to the embryo. The chorion also is important for dissolving mineral from the shell and making it available to the chick for forming bones.
7 days - tiny human implants in mother’s uterus.
10 days - mother’s menses stop.
18 days - heart begins to beat.
21 days - pumps own blood through separate closed circulatory system with own blood type.
28 days - eye, ear and respiratory system begin to form.
42 days - brain waves recorded, skeleton complete, reflexes present.
7 weeks - photo of thumbsucking.
8 weeks - all body systems present.
9 weeks - squints, swallows, moves tongue, makes fist.
11 weeks - spontaneous breathing movements, has fingernails, all body systems working.
12 weeks - weighs one ounce.
16 weeks - genital organs clearly differentiated, grasps with hands, swims, kicks, turns, somersaults, (still not felt by the mother.)
18 weeks - vocal cords work – can cry.20 weeks - has hair on head, weighs one pound, 12 inches long.
23 weeks - 15% chance of viability outside of womb if birth premature.*
24 weeks - 56% of babies survive premature birth.*
25 weeks - 79% of babies survive premature birth.*
For nine months the placenta feeds and nourishes the foetus while also disposing of toxic waste. Without it the foetus would not survive. After the baby is born, the placenta, while thought by most to no longer serve a function, actually has two. If not severed, it supplies the symbiote foetus with oxygenated blood cells as it makes the transition to become an air-breathing infant and it contains all the nutrients and ingredients needed by the mother to replenish those excreted during the birth process and thus help her body recover.
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