Ch. 11 - Human Reproduction

Subdecks (2)

Cards (53)

  • Reproduction
    • The production of new individuals
    • can be asexual or sexual
  • Asexual Reproduction
    • production of offspring from one parent only
  • Sexual Reproduction
    • the production of offspring from two parents
    • e.g. humans
    • involves two parents
    • each parent produces sex cells (gametes)
    • male gametes = sperm
    • female gametes = eggs
  • Sexual Intercourse
    Sexual intercourse (which is also called copulation) takes place when the erect penis of the male is placed in the vagina of the female.
    The movement of the penis in the vagina causes semen to be released from the penis.
  • Sperm in the Vagina
    Normally, millions of sperm are released into the vagina. The sperm move through the cervix and into the uterus. They then move from the uterus towards a fallopian tube.
    After ovulation, the egg is pushed along the fallopian tube by tiny hairs. Many sperm are attracted by a chemical released from the egg. The sperm swarm around the egg in the fallopian tube. Soon the head of one of the sperm will enter the egg.
    If there is no egg present in the fallopian tube, the sperm die, normally within five days.
  • Fertilisation
    • Fertilisation takes place when the nucleus of a sperm joins or fuses with the nucleus of an egg.
    • Fertilisation normally takes place in the fallopian tube. The fertilised egg forms a single cell called a zygote.
  • Process of Fertilisation
  • Pregnancy
    • Once the zygote has formed it goes through many cell divisions to form a ball of cells. These cells then form an embryo.
    • Within a few days of fertilisation, the embryo becomes attached to the lining of the uterus.
    • This attachment is called implantation.
    • Soon after this, the embryo becomes surrounded by a membrane called the amnion.
    • This membrane fills up with a liquid called amniotic fluid. Amniotic fluid acts as a shock absorber to protect the embryo (or baby) during pregnancy.
  • Pregnancy pt. 2
    • After 8 weeks, the embryo can be recognised as a human. At this stage, it is called a foetus.
    • Pregnancy normally lasts from implantation until birth. A normal pregnancy lasts around 40 weeks (about 9 months).
  • Pregnancy - Diagram
  • Process of Sexual Reproduction
  • Placenta
    • A structure called the placenta forms early in pregnancy.
    • The baby's blood passes through the umbilical cord to and from the placenta.
    • The placenta attaches to the lining of the uterus.
    • The umbilical cord attaches to the baby at the navel (belly button).
  • Function of the Placenta
    The function of the placenta is to allow materials to pass between the mother and the baby in the uterus. These materials pass by diffusion.
    • Food and oxygen pass from the mother's blood into the baby's blood
    • Waste products (such as carbon dioxide and salts) pass from the baby to the mother
    • Along with these useful functions, the placenta also allows harmful substances, e.g. alcohol, smoke and drugs, to pass into the baby
  • Stage 1 of Birth
    • Towards the end of pregnancy, muscles in the uterus begin to contract.
    • These contractions are called labour.
    • The contractions cause the amnion to burst.
    • The release of the amniotic fluid through the vagina is called 'the breaking of the waters.
  • Stage 2 of Birth
    • The cervix gradually widens during these contractions. The contractions cause the baby to be pushed head first out through the cervix and the vagina.
    • The umbilical cord is clamped (to prevent loss of blood from the baby) and then cut.
    • The baby soon starts to breathe through its lungs for the first time.
  • Stage 3 of Birth
    • The uterus continues to contract after the baby is born.
    • These contractions push the placenta and the remains of the umbilical cord out of the vagina.
    • These materials are called the afterbirth.
    • The remains of the umbilical cord fall away from the baby's navel after about 7 days.
  • Growth of the Baby
    The baby may feed on breast milk produced by the mother. The main benefits of breastfeeding are:
    • Breast milk is full of the ideal nutrients that a young baby needs
    • Breast milk contains antibodies, which help to protect the baby from infections.
  • Main Medical, Ethical & Societal Issues Surrounding Sexual Reproduction
    The area of sexual reproduction presents many issues for debate in terms of topics:
    • Relating to our health
    • That test our beliefs
    • That relate to the society we live in.
    Some of these topics are discussed in the following sections.
  • Medical Issues - Contraception
    • Contraception is the deliberate use of artificial methods to prevent pregnancy.
    • Some couples want to control the number of children they have or to control how soon after each other their children are born.
    • Others wish to have sexual intercourse without the female becoming pregnant.
    • These couples may use contraception as a method of birth control, or family planning, in order to prevent unwanted pregnancies.
    • There are two main types of contraception:
    1. Preventing fertilisation
    2. Preventing implantation.
  • Preventing Fertilisation - Natural Methods
    • Natural methods of preventing the sperm from reaching the egg are based around avoiding intercourse during the female's fertile period.
    • These methods aim to predict or detect the time of ovulation.
  • Preventing Fertilisation - Artificial Methods
    Artificial methods of contraception include stopping the female from producing eggs.
    This can be achieved by the female taking the contraceptive pill.
    Other artificial methods involve preventing the sperm from reaching the egg. These methods include:
    • The use of a condom, which covers the top of the penis
    • A cap, which covers the cervix
    • Chemical creams or foams, which kill sperm
    • Medical operations in which the sperm ducts or fallopian tubes are cut and sealed.
  • Preventing Implantation
    • Some pills prevent pregnancy by stopping the embryo from attaching (or implanting) in the uterus.
    • A T-shaped device inserted by a doctor in the uterus also acts in this way (Intrauterine Device (IUD))
  • Contraceptive Methods
  • Ethical Issues
    • Ethics means whether conduct is right or wrong.
    • Some couples may decide that a number of contraceptive methods are not acceptable to them.
    • This may be because they are not reliable enough or that they do not agree with them, i.e. ethically, or because of their religious belief system.
  • Societal Issues
    • Different societies have different views on contraception.
    • These views are often reflected by the laws in a country or state.
  • In Vitro Fertilisation - Medical Issues
    • Infertility is the inability to have offspring. Slightly more than one in six Irish couples are infertile.
    • Some of these couples may use in vitro fertilisation (IVF) treatment in order to have a child.
    • IVF involves taking eggs from the female and taking sperm from the male and allowing them to fertilise outside of the body (i.e. in a container such as a petri dish).
  • In Vitro Fertilisation - Medical Issues pt. 2
    • If fertilisation is successful, one (or more) of the embryos is placed into the uterus of the female.
    • The hope is that the embryo(s) will implant and develop in the uterus just as in a normal pregnancy.
    • The process is called in vitro fertilisation because the sperm and the egg join together outside the body of the female.
  • Advantages of IVF
    • IVF allows a couple who are unable to achieve fertilisation naturally to have a child.
    • The child develops normally in the uterus.
  • Disadvantages of IVF

    • There is a small risk of more than one embryo developing (and multiple pregnancies increase the risk of premature births or low birth weight). Some people consider multiple births an advantage.
    • There may be some side effects of the drugs that are taken to allow IVF.
    • There is a slightly higher risk of the baby being born with a birth defect.
    • It is a costly process that often does not result in pregnancy.
  • IVF - Ethical Issues
    Some people feel that IVF is wrong for one or more of the following reasons:
    • It is not a natural process
    • Not all of the embryos are used, and those that are not used are destroyed or used for stem cell research (see next page)
    • There is an increased risk of birth defects.
  • IVF - Societal Issues
    • Different societies have different views on IVF.
    • These views are often reflected by the laws in a country or state.
  • Stem Cells - Medical Issues
    • Stem cells are cells that can develop into any type of body cell.
    • They are often used to learn how structures in the body are formed and to test the effect of new drugs.
    • It is hoped that stem cells will provide treatments for problems such as spinal cord injuries, heart diseases, strokes, Parkinson's disease, and many other disorders.
    • In addition, they may be used to form new healthy structures for use in transplants.
    • Stem cells can be obtained from 3-to 5-day-old embryos, from umbilical cords and from adult sources such as bone marrow, fat and nose cells.
  • Stem Cells - Ethical Issues
    Embryonic stem cells are often obtained from embryos left over after IVF treatment.
    Some people believe that using stem cells from embryos is wrong as it destroys a potential life.
    Others feel that the possible benefits outweigh this issue.
  • Stem Cells - Societal Issues
    Different societies have different views on the use of stem cells. The basic problem is the conflict of two sets of values:
    1. The duty to prevent or reduce suffering
    2. The duty to respect the value of human life
    • In some countries or states the use of all stem cells is banned by law.
    • In others the use of all stem cells is legal. In yet other countries the use of non-embryonic stem cells is legal.
    • Some countries do not have any clear guidelines on stem cells, as it is a relatively new issue.