Human Reproduction

Overview

This lesson will cover:
  1. Sexual reproduction
  2. Male and female reproductive systems
  3. Puberty
  4. The menstrual cycle
  5. Fertilisation
  6. Pregnancy
  7. Family planning

Objectives

By the end of this lesson you will be able to:

  1. Describe and give the functions of the male and female reproductive systems.
  2. Explain the different events that happen throughout the menstrual cycle.
  3. Describe fertilisation and the events after fertilisation.
  4. Understand family planning.
  1. Sexual reproduction

    Humans have two sexes - male and female. For sexual reproduction to occur, sex cells or gametes from the male and female must meet and fuse to form a single cell called a zygote. The zygote then divides many times to form a baby. The male sex cell is called a sperm and is produced in the testes. The female sex cell is called an ovum or egg and is produced in the ovary.

  2. Male and female reproductive systems

    Male reproductive system
    The penis carries the sperm and releases them into the woman's vagina. Sperm are produced in the testes. Testosterone, a male hormone, is also produced in the testes. The scrotal sacs hold the testes. The testes are kept outside the body at a temperature of 35o Celsius, which is lower than the normal body temperature of 37.5o Celsius. Sperm develop best at this temperature. The path taken by the sperm from the testes to the penis can be seen if we take a side view of the male reproductive system. The sperm duct carries the sperm from the testes to the urethra. The ureter is a tube that carries urine from the kidney to the bladder. The bladder stores urine. The urethra in the penis carries urine from the bladder to the outside. The urethra carries sperm to the outside during intercourse. Different glands add fluid to the sperm as they pass along the sperm duct. This mixture of fluid and sperm is called semen. A sperm is a sex cell made up of a head and a tail. The nucleus in the head contains the genes while the tail is used for movement.

    Female reproductive system
    The ovaries produce the eggs or ova. Oestrogen, a female hormone, is also produced in the ovaries. The embryo develops inside the womb or uterus. During intercourse the penis is inserted inside the vagina. At birth the baby passes down the vagina to the outside. The side view of the female reproductive system shows us the path taken by the egg as it travels to the womb. Approximately once a month an egg is released from an ovary. The egg is collected by the fallopian funnel and travels along the fallopian tube to the uterus. The ureter carries urine from the kidney to the bladder. The urethra carries urine to the outside.


  3. Puberty

    Puberty begins between the ages of 10 and 15 years in boys and girls, when various bodily changes take place. Glands such as the testes and the ovary produce chemical substances called hormones. Hormones are transported in the blood to different parts of the body and cause changes in tissues and organs. In boys, the testes release a hormone called testosterone. Testosterone causes the penis to grow and hair to develop under the arms and around the genitals. It also makes the voice deepen, promotes muscular development and initiates sperm production. Oestrogen, the female sex hormone, is produced in the ovaries. Oestrogen causes hair growth under the arms and around the genitals, breast development and widening of the hips. It also initiates the menstrual cycle.

  4. Menstrual cycle

    The menstrual cycle describes the changes that take place in a woman's body approximately every twenty-eight days. The menstrual cycle prepares the woman's body for pregnancy. For the first four to five days of the cycle the lining of the womb breaks down and along with some blood, flows out of the womb. This is called menstruation. After menstruation the lining of the womb is rebuilt from day six to day fourteen. Around day fourteen an egg is released from the ovary. This is called ovulation. The egg or ovum travels along the fallopian tube to the uterus. As the egg moves along the fallopian tube, the rebuilding of the womb is completed. If the egg is not fertilised while in the fallopian tube, it passes into the womb and out through the body via the vagina. The lining of the uterus remains intact until about day twenty-eight of the cycle and if fertilisation has not occurred, the lining breaks down and the cycle restarts. The average length of the menstrual cycle is twenty-eight days and menstruation occurs nearly once a month in a woman's body. Between the ages of forty-five and fifty-five, ovaries stop releasing eggs. This is called the menopause.

    Copulation
    Sperm cells must be placed inside a woman's body for fertilisation to occur. For this to happen, sexual intercourse or copulation must take place. The penis becomes stiff and erect. The penis is placed inside the woman's vagina. Up to two million sperm are released or ejaculated into the vagina by the penis. The sperm swim up through the uterus and into the fallopian tube.


  5. Fertilisation

    An egg must be present in one of the fallopian tubes for fertilisation to take place. An egg can survive for about twenty-four hours in the fallopian tubes. If intercourse takes place before ovulation, fertilisation can still take place as the sperm can survive in the woman's body for up to three days. Fertilisation occurs when the sperm and the egg meet and the nucleus of the sperm fuses with the nucleus of the egg cell to form a new single cell called a zygote.

    Events after fertilisation
    After fertilisation the zygote continues to move down the fallopian tube to the uterus. The egg divides into two, then four, then eight and so on until a ball of cells is formed. The journey to the womb can take up to seven days. During this time the lining of the womb prepares to receive the embryo. When the ball of cells reaches the womb it is called an embryo. The embryo attaches itself to the womb wall. This is called implantation or conception. Blood vessels in the womb wall nourish the growing embryo.


  6. Pregnancy

    The human baby takes about forty weeks to develop in the womb. In the womb, the ball of cells continues to divide to form the different parts of the human body. By the end of eight weeks, all the tissues and organs are formed. The embryo is three centimetres long and weighs only four grams. From then onwards the embryo is called a foetus. During the next thirty-two weeks the tissues and organs develop further. The placenta is fully developed by the ninth week. The placenta is a special organ that passes food, oxygen and water from the mother's blood to the baby's blood. Carbon dioxide and waste pass from the baby's blood to the mother's blood. The foetus is connected to the placenta by a tube called the umbilical cord. The baby rests in a fluid filled bag that protects it from shocks and mechanical damage.

    Birth
    Just before the baby is born the bag of fluid bursts. This is called the breaking of the waters. Normally the baby exits through the vagina head first. Contractions of the uterus force the baby out. This is called labour. After the baby is born the umbilical cord is clamped and then cut. About fifteen minutes after the birth the placenta is delivered. This is the afterbirth.


  7. Family planning

    Sometimes parents wish to control the number of children they have. This is called family planning. The natural method of family planning is based on the menstrual cycle. Fertilisation can only happen during a woman's fertile period. Ovulation takes place during this period. If sexual intercourse is avoided during this period, fertilisation will not happen, as the sperm will not meet the egg. Taking a woman's temperature can monitor the time of the month when ovulation takes place. The temperature rises slightly at ovulation. A woman can predict when ovulation is most likely to occur by charting her temperature on a daily basis for a few menstrual cycles.

    Contraceptives can be used for artificial methods of family planning. The condom or sheath, when placed over the penis, prevents sperm gaining entry to the womb. Other barrier methods such as the diaphragm, the cervical cap and the contraceptive sponge, when placed over the entrance to the womb, prevent sperm from entering the womb and thus fertilising the egg. There are many different types of contraceptive pills; some work by preventing ovulation from taking place and others by thickening the mucus at the entry to the womb thus preventing the sperm from gaining entry. The "morning after" pill prevents implantation of the fertilised egg by making the lining of the womb hostile to the fertilised egg. The coil, which is a device made of plastic and copper, when inserted into the womb wall, prevents implantation of the fertilised egg.

    Summary

    This lesson has covered:
    1. For sexual reproduction to occur, sex cells or gametes from the male and female must meet and fuse to form a single cell called a zygote.
    2. The male sex cell is called a sperm and is produced in the testes.
    3. The female sex cell is called an ovum or egg and is produced in the ovaries.
    4. The sperm duct carries the sperm from the testes to the urethra.
    5. Approximately once a month, an egg is released from an ovary, collected by the fallopian funnel and travels along the fallopian tube to the uterus.
    6. Puberty begins between the ages of 10 and 15 years in boys and girls, when various bodily changes take place.
    7. The menstrual cycle describes the changes that take place in a woman's body approximately every twenty-eight days.
    8. Menstruation takes place for the first four to five days of the cycle when the lining of the womb breaks down.
    9. Ovulation takes place around day fourteen when an egg is released from the ovary.
    10. Copulation occurs when the penis is placed inside the woman's vagina.
    11. Ejaculation is the release of sperm by the penis.
    12. Fertilisation occurs when the sperm and the egg meet and the nucleus of the sperm fuses with the nucleus of the egg cell to form a new single cell called the zygote.
    13. After fertilisation the zygote continues to move down the fallopian tube to the uterus.
    14. The fertilised egg divides many times until a ball of cells is formed.
    15. Implantation or conception occurs when the embryo attaches itself to the womb wall.
    16. The human baby takes about forty weeks to develop in the womb.
    17. The placenta is a special organ that passes food, oxygen and water from the mother's blood to the baby's blood.
    18. Carbon dioxide and waste pass from the baby's blood to the mother's blood.
    19. Just before the baby is born the bag of fluid protecting the baby bursts.
    20. Contractions of the uterus force the baby out. This is called labour.
    21. About fifteen minutes after the birth, the placenta or afterbirth is delivered.
    22. The natural method of family planning is based on the menstrual cycle.
    23. Contraceptives can be used for artificial methods of family planning. .