human reproduction

• Reproduction


  The production of new individuals
• Sexual reproduction


  How humans reproduce
• Gamete


  Sex cell
• Sperm


  Male gamete
• Egg


  Female gamete
• Parts of the male reproductive system

  • Sperm duct
  • Urethra
  • Penis
  • Scrotum
  • Testis
• Testis


  Makes sperm
• Changes that take place in a boy's body at puberty

  • Enlargement of penis and testes
  • Rapid growth in size and height
  • Voice box enlarges causing the voice to deepen
  • Growth of hair on the body
• Sperm


  Extremely small, produced in massive numbers by the testes, function of the tail is to help the sperm swim
• Scrotum


  Sac in which the testes are held, holds the testes outside the body because sperm are made successfully at a temperature just lower than body temperature
• Sperm ducts


  Two ducts that carry sperm from each of the testes to the penis, glands in the sperm ducts produce a liquid called seminal fluid, the mixture of sperm and seminal fluid is called semen
• Penis


  The sperm ducts connect to a tube called the urethra, sperm pass through this tube which is located in the centre of the penis, the penis allows sperm to pass out of the male body and into the female body
• Parts of the female reproductive system

  • Ovary
  • Fallopian tube
  • Uterus
  • Cervix
  • Vagina
• Ovary


  Produces eggs (female gamete), egg production begins at puberty (aged 10-13 years), one egg is formed each month, egg production slows down at age 35 and stops between 35-55 years, this is called the menopause
• Changes that take place in a girl's body at puberty

  • Growth of the pelvis, breasts, vagina, and uterus
  • Growth of hair on parts the body
• Fallopian tube


  Collects the egg from the ovary and carries it to the uterus, if sperm are present one may fertilise the egg in the fallopian tube, if no sperm are present the egg will die within two days
• Uterus


  The place in which a baby (or embryo) will develop
• Vagina


  A muscular tube into which the penis releases sperm, also forms the birth canal when the baby passes down the vagina at childbirth
• Cervix


  The opening of the uterus, sperm will pass through the cervix to reach an egg
• Closing the fallopian tubes prevents pregnancy by blocking the egg from reaching the uterus and preventing sperm from reaching the egg, thus preventing fertilisation
• Cutting or sealing the sperm ducts prevents pregnancy by preventing sperm from travelling from the testes, through the urethra and out of the penis, thus preventing fertilisation
• Menstrual cycle


  In females, one cycle takes place approximately every 28 days between puberty and the menopause, the cycle does not take place if the female is pregnant
• What happens during the menstrual cycle

  1. Days 1 to 5: The lining of the uterus breaks down and is passed out of the body through the vagina (menstruation or having a period)

  2. Days 6 to 13: A new lining develops in the uterus, the egg will continue to develop in the ovary

  3. Day 14: An egg is released from the ovary (ovulation), the egg can only survive for two days in the fallopian tube

  4. Day 15 to 28: The lining of the uterus remains in place, it will break down on the first day of the next menstrual cycle resulting in menstruation or period
• Fertile period


  The part of the menstrual cycle where the female is most likely to become pregnant (normally days 9 – 16), sperm can stay alive in the female for 5-7 days, the egg can stay alive for two days
• Sexual intercourse


  Also called copulation, occurs when the erect penis of the male is placed in the vagina of the female, movement of the penis in the vagina then causes semen to be released
• What happens to sperm in the vagina


  Millions of sperm are released into the vagina, sperm will swim from the vagina to the cervix, uterus and fallopian tube, the egg is pushed down the fallopian tube by tiny hairs, sperm will swim around the egg in the fallopian tube, eventually the head of one sperm will enter the egg
• Fertilisation


  Occurs when the nucleus of the sperm joins with the nucleus of an egg, this occurs in the fallopian tube, the fertilised egg will then form a zygote
• How identical twins are formed

  One egg has been fertilized by one sperm, the zygote splits into two at the very earliest stage of development, when the zygote is no more than a few cells, dividing this early means each baby has exactly the same genetic information
• How non-identical twins are formed

  The female releases two eggs during ovulation instead of one, both of these eggs are then fertilised by the male sperm to form a zygote, these twins will not be identical as they have different genetic information from different sperm and eggs
• Pregnancy


  Once the cell has been fertilised a zygote is formed, this zygote then goes through many cell divisions to form a ball of cells, these cells then form an embryo (offspring in the process of development), the embryo will attach itself to the lining of the uterus (implantation), soon after implantation the embryo will become surrounded with a membrane that fills with a fluid called amniotic fluid, this amniotic fluid protects the baby during pregnancy, it is not until 8 weeks that the embryo can be recognised as a human, at 8 weeks the embryo is now known as a foetus
• Placenta


  Forms in early pregnancy, the baby's blood passes through the umbilical chord to and from the placenta, the placenta attaches to the lining of the uterus, the umbilical chord attaches to the baby at the navel
• Functions of the placenta

  • Allows food and oxygen to pass from the mother's blood into the baby's blood, allows waste products (carbon dioxide and salts) to pass from the baby to the mother, can also allow harmful substances like alcohol, smoke, and drugs to pass from the mother to the baby
• What happens at birth

  Towards the end of pregnancy muscles in the uterus of the mother begin to contract (labour), these contractions cause the amnion to burst releasing amniotic fluid (the breaking of the waters), the contractions will cause the cervix to widen and the baby to be pushed out head first through the cervix and vagina, the umbilical chord is cut and clamped shut, the uterus contracts after the baby is born to push out the remains of the umbilical chord and placenta (afterbirth)
• Growth of the baby

  • The baby may feed on breast milk produced by the mother, breast milk contains many nutrients and antibodies to help the baby grow and protect it from infections
• Contraception


  The deliberate use of artificial methods to prevent pregnancy, some couples use it to control the number of children they have or to prevent pregnancy during sexual intercourse, there are two types - those that prevent fertilisation and those that prevent implantation
• Methods that prevent fertilisation

  • Natural methods based on avoiding sexual intercourse during the fertile period
  • Artificial methods like stopping the female from producing eggs, preventing sperm from reaching the egg, covering the penis, or placing a barrier inside the vagina
• IVF (in vitro fertilisation)

  IVF treatment can help couples who suffer from infertility, it involves taking eggs from the female and sperm from the male and allowing fertilisation to take place outside the body, if successful the embryo is then placed into the uterus of the female
• Advantages and disadvantages of IVF

  • Advantages: Helps couples who cannot have a child to have a child

  Disadvantages: Higher risk of multiple births, slightly higher risk of birth defects, side effects of drugs taken