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natural science unit 3
The female reproductive system:
They are the physical differences between men and women.
Primary sexual characteristics:
are the differences between male and female reproductive organs.
Secondary sexual characteristics:
are other physical differences between men and women.
The female reproductive organs:
most of the female reproductive organs are internal.
They are located in the lower abdomen:
Ovaries contain female reproductive cells aclled ova.
One ovum matures each month.
Women is borned with all the ova they will need for the rest of their lifes.
Conect the ovaries to the uterus.
It is an organ with muscular walls.
During pregnancy a fertilised cell develops into a baby here.
The part of the uterus that leads to the vagina is called the cervix
It is a muscular tube which connects the uterus to the outsido of the body.
The vulva is on the outside of the body and covers the opening of the vagina.
Puberty in girls:
A girl starts puberty between 10 and 16 years old.
The breasts begin to develop.
Pubic hair grows.
Glands in the skin and scalp produce more oil which can cause spots or acne.
Armpit hair begins to grow.
Menstruation starts between 10 and 15 years.
The menstrual cycle:
An ovum is released from the ovaries into the fallopian tubes about every 28 days. This process is called ovulation.
The walls of the uterus get thicker with extra blood and tissue in preparation for fertilisation.
If fertilisation does not happen, the ovum dries up and leaves the body through the vagina about two weeks later.
Blood and thickened lining of the uterus comes away too. This is menstruation.
Menstruation typically lasts from 3 to 5 days.
Women menstruate until they have no eggs left.
This usually happens when a woman is about 50.
This period is called menopause.
The male reproductive system:
The male reproductive reproductive system produces and transports sperm cells.
It has an oval shape and a tail.
The tail allows it to move up the female´s fallopian tubes and fertilise the ovum.
Men produce millions of sperm every day.
The male reproductive organs:
most male reproductive organsare external.
The testicles produce and store sperm.
The testicles are located in a bag of skin called the scrotum.
The scrotum regulates the temperature of the testicles
Sperm travels through two tubes called the vasa deferentia to the seminal vesicles.
The seminal vesicles produce a liquid that forms part of semen.
The prostate produces a liquid that forms part of semen.
semen carries the sperm and gives it nutrients.
he penis contains the urethra.
The sperm travels through the urethra to the outside of the body.
The urethra also expels urine.
Puberty in boys:
When boys reach puberty, the brain secretes hormones which activate the testicles to produce testosterone.
This hormone brings many physical changes:
The testicles enlarge.
the scrotum becomes larger and thicker.
The penis grows longer and thicker and boys become fertile.
sperm mixes with seminal fluid toform semenwhich is ejaculated from the penis.
Pubic hair grows.
They become taller and heavier.
The voice deepens.
hair grow under the arms and on the face.
The skin becomes coarser and can be oily or develop acne.
Humans pass on some characteristics to their offspring through genes.
mans have about 24000 genes.
Parents pass onto their children characteristics such as eye and hair colour.
Pregnancy and birth:
Human reproduction involves two different sex cells: a female ovum and a male sperm.
Fertilisation of the ovum can occur after the egg is released into the fallopian tubes.
During sexual intercourse the man´s penis is insterted into the woman´s vagina and the sperm is deposited there.
Then using their tails they swim up the vigina to the ovum in the fallopian tube.
Only one sperm can fertilise an ovum.
Once the ovum is fertilised, the cells start to divide and multiply.
This ball of cells is called a zygote.
Development of the embryo:
The zygote travels to the uterus where its cells carry on dividing and multiplying until they become an embryo.
The embryo fixes itself onto the lining of the uterus where it ill continue to grow.
At 8 weeks, the embryo is about the size of an adults´s thumb.
Development of the foetus:
After about 9 weeks, all the organs have formedand and the embryo develops into a foetus.
e foetus floats in a sac of amniotic fluid which protects it from knoks and bumps.
The foetus receives oxygen from the moter´s placenta.
Waste matter and carbon dioxide are transfered from the foetus to the mother via the placenta.
The baby is connected to the placenta by the umbilical cord.
Pregnancy lasts about 280 days.
When the foetus is ready to be born, it pushes against the cervix, which starts to open.
Amniotic fluid is released which is often the first sign that birth is about to start.
The muscles of the uterus begin to contract and the cervix opens sufficiently to allow the baby to pass.
The baby is pushed through the cervixand along the birth canal.
Babies are usually born head first.
The umbilical cord comes out with the baby.
This is cut and tied, and forms our navel.
The placenta comes out after the baby.