3rd TOPIC. SIXTH LEVEL. REPRODUCTION. Human sexual characteristics. There are two types of human sexual characteristics: _ Primary sexual characteristics enable human beings to reproduce. We have these when we are born. _ Secondary sexual characteristics differentiate men and women. They develop at puberty. _ Men have lower voices , more developed muscles and a lot of facial and body hair. _ Women have higher voices , breasts , wider hips and little body hair . Puberty Puberty occurs when the reproductive system matures. Puberty starts when the pituitary gland sends hormones to the genital organs.  
Girls reach puberty between the ages of 11 and 14. Boys reach puberty between the ages of 13 and 15.
3rd TOPIC. SIXTH LEVEL. REPRODUCTION.
The female reproductive system. The female internal genital organs are: The ovaries : they produce the eggs necessary for reproduction.
The Fallopian tubes : they connect the ovaries to the uterus. The uterus : it is the organ where the baby develops during the pregnancy.
_ The vagina : it is a channel which goes from the uterus to the outside of the body. The vulva is the external part of the female reproductive system.
3rd TOPIC. SIXTH LEVEL. REPRODUCTION.
The male reproductive system. The male internal genital organs are : Two testicles : they produce the sperm cells necessary for reproduction.
The vas deferens : sperm travels through this tube to the urethra.
The urethra : sperm travels through this passage to the outside of the body.
The seminal vesicles and the prostate gland : they produce a liquid to feed and transport sperm.
3rd TOPIC. SIXTH LEVEL. REPRODUCTION.
The male external genital organs are :  The scrotum: it is a bag of skin which contains the testicles .  The penis : the urethra passes through this organ. The urine and the sperm leave the body through the urethra. Sex
cells.
The female sex cells are: Egg cells, they are large and round . From puberty on , one egg matures and passes through a Fallopian tube approximately every 28 days . If the egg cell is not fertilized, it leaves the body through the vagina . Minor bleeding occurs,called menstruation or a period .
3rd TOPIC. SIXTH LEVEL. REPRODUCTION.
The male sex cells are: Sperm , they are very small , about 200 million of these are produced every day.
Fertilisation Fertilisation occurs when an egg cell and a sperm unite in one of the Fallopiantubes or in the uterus.
The sperm enters the egg and fertilises it. They form a new cell called a zygote . The zygote travels to the uterus and
3rd TOPIC. SIXTH LEVEL. REPRODUCTION. attaches itself to the uterus wall .In the uterus , the zygote starts to divide itself into two , four , eight , and so on .When it consists of about 100 cells , it is called an embryo. After that , the placenta starts to form .The umbilical cord connects the embryo to the placenta so it can receive nutrients and oxygen from the mother´s body. Pregnancy An embryo continues to grow for 39 or 40 weeks. This period of time is called pregnancy. After 9 weeks the embryo starts to look like a baby and is called a foetus. It has hands, feet, ears and eyes. After 4 months all the baby´s organs are formed. After 6 months the baby can hear, perceive light and react.
After 9 months the baby measures about 50 cm and weighs about 3 kilos . It is ready to be born.
3rd TOPIC. SIXTH LEVEL. REPRODUCTION.
Birth Birth begins when the baby´s mother feels muscular contractions that will push the baby out through the vagina. When the baby is born, the umbilical cord is cut. Later the placenta is expelled. Babies can feed on milk from their mothers´ breasts. Boys and girls are considered babies until they are one year old.
3rd TOPIC. SIXTH LEVEL. REPRODUCTION.