The REPRODUCTIVE SYSTEMS.

The human reproductive system. The changes that take place during adolescence as the reproductive system develops are described, as well as the way that the foetus develops in the uterus. It has these parts in it: The male reproductive system The female reproductive system The menstrual cycle Fertilisation and the development of the foetus Puberty The male reproductive system The reproductive system contains the organs needed for reproduction or producing babies. The male reproductive system contains these parts: testes (pronounced "test-eez") glands sperm ducts urethra penis. Male reproductive system Testes The two testes (one of them is called a testis) are contained in a bag of skin called the scrotum. They have two functions: to produce millions of male sex cells called sperm to make male sex hormones, which affect the way a man's body develops. Sperm duct and glands The sperm can pass through the sperm ducts, and mix with fluids produced by the glands. The fluids provide the sperm cells with nutrients. The mixture of sperm and fluids is called semen. Penis and urethra The penis has two functions: to pass urine out of the man's body to pass semen into the vagina of a woman during sexual intercourse. The urethra is the tube inside the penis that can carry urine or semen. A ring of muscle makes sure that there is no chance of urine and semen getting mixed up. The female reproductive system The female reproductive system contains these parts: ovaries egg tubes uterus (pronounced "yoo-ter-russ") cervix vagina. Female reproductive system Ovaries The two ovaries contain hundreds of undeveloped female sex cells called egg cells or ova. Women have these cells in their bodies from birth - whereas men produce new sperm continually. Egg tubes Each ovary is connected to the uterus by an egg tube. This is sometimes called an oviduct or Fallopian tube. The egg tube is lined with cilia, which are tiny hairs on cells. Every month, an egg develops and becomes mature, and is released from an ovary. The cilia waft the egg along inside the egg tube and into the uterus. Uterus and cervix The uterus is also called the womb. It is a muscular bag with a soft lining. The uterus is where a baby develops until its birth. The cervix is a ring of muscle at the lower end of the uterus. It keeps the baby in place while the woman is pregnant. Vagina The vagina is a muscular tube that leads from the cervix to the outside of the woman's body. A man's penis goes into the woman's vagina during sexual intercourse. The opening to the vagina has folds of skin called labia that meet to form a vulva. The urethra also opens into the vulva, but it is separate from the vagina, and is used for passing urine from the body. The menstrual cycle The female reproductive system includes a cycle of events called the menstrual cycle. It lasts about 28 days, but it can be slightly less or more than this. The cycle stops while a woman is pregnant. These are the main features of the menstrual cycle. The start of the cycle, day 1, is when bleeding from the vagina begins. This is caused by the loss of the lining of the uterus, with a little blood. This is called menstruation or having a period. By the end of about day 5, the loss of blood stops. The lining of the uterus begins to re-grow and an egg cell starts to mature in one of the ovaries. At about day 14, the mature egg cell is released from the ovary. This is called ovulation. The egg cell travels through the egg tube towards the uterus. If the egg cell does not meet with a sperm cell, the lining of the uterus begins to break down and the cycle repeats. If the egg cell meets and joins with a sperm cell, it is fertilised. It attaches to the lining of the uterus and the woman becomes pregnant. Fertilisation and the development of the foetus Fertilisation Fertilisation happens when an egg cell meets with a sperm cell and joins with it. This happens after sexual intercourse in which a man puts his penis into the woman's vagina. Sperm cells travel in semen from the penis and into the top of the vagina. They enter the uterus through the cervix and travel to the egg tubes. If a sperm cell meets with an egg cell there, fertilisation can happen. The fertilised egg divides to form a ball of cells called an embryo. This attaches to the lining of the uterus and begins to develop into a foetus (pronounced "fee-tuss") and finally a baby. Development of the foetus The foetus relies upon its mother as it develops. These are some of the things it needs: protection oxygen nutrients (food and water). It also needs its waste substances removing. The foetus is protected by the uterus and the amniotic fluid, a liquid contained in a bag called the amnion. The placenta is responsible for providing oxygen and nutrients, and removing waste substances. It grows into the wall of the uterus and is joined to the foetus by the umbilical cord. The mother's blood does not mix with the foetus's blood, but the placenta lets substances pass between the two blood supplies: oxygen and nutrients diffuse across the placenta from the mother to the foetus waste substances, such as carbon dioxide, diffuse across the placenta from the foetus to the mother. Birth After nine months the baby is ready to be born. The cervix relaxes and muscles in the wall of the uterus contract, pushing the baby out of the mother's body. Puberty The reproductive system of a child is not mature and needs to change as a boy or girl develops into an adult, so that the system is fully working. These changes begin between the ages of ten and fifteen. The time when the changes happen is called puberty. The changes happen because of sex hormones produced by the testes in boys and by the ovaries in girls. Some changes happen in boys and girls, while others just happen in boys or girls. Here are some changes that happen to boys and girls: underarm hair grows pubic hair grows body smell gets stronger. There are also emotional changes at this time, and a growth spurt. The time when the physical changes and emotional changes happen is called adolescence. Graph of heights Here are some changes that only happen to boys: voice breaks (gets deeper) testes and penis get bigger testes start to produce sperm cells shoulders get wider hair grows on face and chest. Here are some changes that only happen to girls: breasts develop ovaries start to release egg cells (periods start) hips get wider.