chapter 16

• Fertilisation: fusion of the nucleus of the sperm and egg to form a zygote

  • 23 chromosomes from each parent
  • zygote -> embryo -> foetus
• Heredity: passing down of genetic material from one generation to the next during sexual reproduction

  • siblings are unique individuals (not identical)
  • inheriting traits is a random process

  _ many unique combinations of genetic material

  _ each offspring inherits any combination

  _ causes similarities and differences

  • inhertitable diseases — undesirable

  _ sickle-cell anaemia (blood)

  _ cystic fibrosis (lungs and other organs)
• Puberty (usually age 11-14)

  : period during which body undergoes various physical changes and matures sexually

  Hormones: chemicals produced by glands in our body which control and coordinate activities throughout body by triggering other organs to function

  -> needed in small amounts, transported by blood to alter activity of organs
• puberty in girls

  • height and weight increase
  • breasts begin to develop
  • hips become broader and rounder
  • armpit and pubic hair around sex organs appear
  • maturation of eggs begins
• puberty in boys

  • height and weight increase
  • voice deepens
  • facial, armpit and pubic hair around sex organs appear
  • muscle strength increases
  • production of sperm begins
• male reproductive system

  • sex glands - produce nutrient fluid to nourish sperm and provide them with energy to move
  • sperm duct - carries sperm from testes to urethra
  • urethra - tube that allows sperm to pass through during ejaculation, also allows urine to pass through
  • penis - deposits semen (mixture of sperm and nutrient fluid) into vagina during ejaculation
  • testis - produce sperms and male sex hormones that control sexual development in body
• female reproductive system

  • oviduct - muscular tube through which the mature egg is released from the ovary. (fertilisation occurs here)
  • ovary - produce eggs and female sex hormones that control sexual development in body
  • uterus - muscular organ where the embryo develops into a foetus during pregnancy. (contains uterine lining)
  • vagina - sperms are deposited here
  • cervix - opening of uterus that connects uterus to vagina
• ovulation - one of the ovaries releases a mature egg cell which enters the oviduct

  • if fertilised: form a zygote -> divides to form embryo -> embryo implants itself into uterine lining -> pregnant
  • if not fertilised: it will break down
• during birth:

  • strong contractions of muscles of uterus push the baby past the cervix, out of mother’s body through the vagina
• fertilisation

  1. penis deposits the semen containing sperm into the vagina
  2. sperm cells swim through the cervix into the uterus and the oviduct
  3. sperm cell meets an egg cell in oviduct
  4. fertilisation occurs when nucleus of the sperm fuses with nucleus of the egg to produce a zygote. all other sperm cells die
  5. as zygote travels to uterus, it divides repeatedly to form an embryo
  6. the embryo implants itself into the uterine lining where it develops into a foetus
  7. after 9 months, the baby is born
• issues with reproductive system

  • testes unable to produce healthy sperm

  _ fertilisation cannot occur

  • female oviducts blocked

  _ sperm unable to swim to oviduct to meet egg

  • affected by age, diet, lifestyle
• days 1 - 5 (menstruation)

  • menstruation: if no fertilisation occurs, uterine lining and blood vessels break down and are discharged with the unfertilised egg

  days 6 - 9

  • uterine lining thickens and many blood vessels are formed in it (prepare uterus for the implantation of embryo if fertilisation occurs)

  days 10 - 15 (fertile period)

  • ovulation (day 14)
  • before day 14: sperm can survive inside FRS for 3 - 5 days
  • after day 14: egg can live in FRS for one day after ovulation — still alive on day 15

  days 16 - 28

  • uterine lining continues to thicken
• birth control methods (temporary — reversible)

  1.rhythm method

  _ do not have sexual intercourse during fertile period (days 10-15 -> unsafe)

  _ unreliable, pregnancy can still occur

  2. condom

  _ thin rubber covering used to cover the penis before sexual intercourse

  _ impermeable to sperms, bacteria and viruses (protects user from STIs)

  3. spermicide

  _ cream that kills sperms in vagina

  _ not reliable — used with condom or diaphragm
• birth control methods (temporary)

  4. intra-uterine device

  _ contains copper, inserted into uterus by a doctor

  _ prevents embryo from implanting in the uterine lining

  _ lasts 3 - 10 years

  5. birth control pills

  _ contains certain female sex hormones which prevent ovulation

  _ prevents release of mature egg each month

  _ side effects

  6. diaphragm

  _ dome-shaped plastic cup with elastic rim

  _ inserted into vagina to cover cervix
• birth control methods (permanent — irreversible)

  1.tubal ligation

  _ cutting and tying both oviducts during surgery

  2. vasectomy

  _ cutting and tying both sperm ducts during surgery

  _sperms will not be ejaculated
• abortion: deliberate termination of a pregnancy

  • illegal to undergo abortion after 6th month in singapore
  • damage to the mother’s uterus may cause bleeding, infertility, infection

  STIs -> diseases mainly transmitted during sexual intercourse

  also by: blood transfusion, sharing of unsterilised or contaminated needles, from mother to infant
• syphilis - bacterial infection

  • painless sores and red rashes
  • infertility
• gonorrhoea - bacterial infection

  • burning sensation during urination
  • discharge of pus from penis or vagina
  • pain in lower abdomen

  long-term effects

  • infertility
  • long-term pelvic or abdominal pain
• HIV - viral infection

  • flu-like symptoms (headache, sore throat, fever, muscle ache, fatigue)

  long-term effects

  • development into AIDS if left untreated, resulting in a weakened immune system
  • complications from other infections
  • death
• • antibiotics treat bacterial infections (eg. syphilis and gonorrhoea), not effective against viral diseases
• growth in world population

  1.medical advancements

  _ new drugs, vaccines

  2. increased food production

  _ crops can now be grown in previously infertile soil, protected against pests

  3. improved transportation

  _ food and medicine supplied to more regions, shorter amount of time

  4. improved sanitation

  _ reduce spread of diseases