Human Reproduction Part 2

• Lutenizing hormone


  Hormone that triggers ovulation
• Follicle stimulating hormone


  Hormone that causes eggs to mature
• Ovarian cycle


  1. Growing follicle

  2. Ovulation

  3. Corpus luteum

  4. Fertile period

  5. Menses

  6. Follicular phase

  7. Luteal phase
• Ovarian cycle hormones


  • FSH causes eggs to mature and stimulates ovary to produce oestrogen
  • LH triggers ovulation
  • Oestrogen causes uterine lining to develop, inhibits FSH, stimulates LH
  • Progesterone maintains uterine lining, inhibits FSH and LH
• Copulation and Fertilization


  1. Sexual stimulation causes blood flow to penis

  2. Erected penis inserted in female's vagina, sperm ejaculated

  3. Sperm swims to ovum

  4. Acrosome of sperm digests ovum's outer membranes, sperm nucleus fuses with ovum nucleus forming zygote
• The ovum has a life span of about 1 day and so fertilization has to occur only in the oviduct
• The sperm may stay for a longer period of time swimming in the oviducts
• Fertilization


  Fusion of ovum and sperm forming a diploid zygote
• The new cell contains a set of genetic material from the mother and a set from the father
• After fertilization


  1. Ovum membrane alters to form barrier to other sperm

  2. Zygote starts to divide into 2 cells, then 4, then a ball of cells (blastula)

  3. Blastula develops into embryo and placenta

  4. Embryo implants in uterus lining to receive nourishment
• Placenta


  • Disc-shaped organ that forms close association between embryo and mother's tissue
  • Composed of cells from fetus and mother
  • Acts as main site of exchange after 12 weeks of pregnancy
• Functions of the placenta

  • Provides physical attachment of fetus to uterus wall
  • Transports nutrients, antibodies, oxygen from mother to child
  • Transports waste products from child to mother
  • Secretes hormones like progesterone to maintain uterine lining
• There is no blood contact between the mother and the child, the placenta acts as a barrier
• Placenta adaptations


  • Large surface area between it and uterus wall
  • Villi (finger-like projections) that increase surface area
  • Rich supply of maternal blood vessels
• Umbilical cord


  Contains blood vessels that carry materials for exchange between mother and fetus
• The umbilical artery carries urea and carbon dioxide from the fetus to the mother's blood
• The umbilical vein carries oxygen and nutrients from the mother's blood to the fetus
• After two months the human embryo is called a fetus
• The fetus is surrounded by a shock absorbing amniotic sac filled with amniotic fluid
• Gestation period


  Time it takes for a fetus to develop in the uterus, about 40 weeks
• Birth


  1. Cervix starts to dilate

  2. Uterus contractions become more frequent and powerful

  3. Oxytocin hormone helps contractions

  4. Amniotic fluid discharged as cervix dilates
• Pregnancy takes about 38 weeks in humans, the baby normally lies with its head against the cervix by the end
• Sequence of events that leads to the birth of a baby

  1. Labour

  2. Cervix starts to dilate

  3. Mild contractions of the uterus muscle

  4. Contractions become more frequent and powerful

  5. Oxytocin helps the contractions

  6. Plug of mucus comes away

  7. Amnion bursts and amniotic fluid is discharged

  8. Cervix dilates

  9. Contractions push the baby downwards

  10. Baby's head is pushed past the cervix

  11. Baby takes its first breath

  12. Umbilical cord is tied and cut

  13. Placenta breaks away and is discharged
• Placenta


  Organ that develops in the uterus during pregnancy and allows for the exchange of nutrients, waste and gases between the mother and fetus
• Uterus


  The organ in which the fetus develops during pregnancy
• The sequence of events that leads to the birth of a baby is called labour
• During the first stage of birth the cervix starts to dilate
• Labour begins with mild contractions of the uterus muscle
• At first the contractions come every 20 minutes or so, but as birth approaches, they become more frequent and more powerful
• Oxytocin


  A hormone produced in the hypothalamus and released from the posterior pituitary gland that helps the contractions of the uterus
• The plug of mucus that blocks the cervix during pregnancy comes away and passes out of the vagina. This is called the show and consists of a sticky pinkish mucus
• Contractions


  1. Cause the amnion to burst and the amniotic fluid to be discharged out through the vagina

  2. Cause the cervix to start becoming wider
• A heartbeat monitor may be strapped around the upper part of the woman's abdomen to check the level of stress of the fetus
• Contractions


  1. Gradually get stronger and more frequent due to the positive feedback control of oxytocin production

  2. Spread down the uterus and are strongest from top to the bottom thus pushing the baby downwards

  3. Cause the cervix to gradually dilate
• Labour


  1. Continues as the baby's head is pushed past the cervix into the vagina

  2. Ends with the rest of the baby's body following much more easily once the head is born
• The sudden fall in temperature felt by the newly born baby stimulates it to take its first breath
• When the baby is breathing properly, the umbilical chord is then tied and cut
• Placenta


  Breaks away from the wall of the uterus and is discharged, leaving the vagina as the afterbirth
• Parental care


  The care provided to the baby, mostly by the mother, especially in the first stages of life
• Breast feeding


  The mother feeding the baby with milk produced in the mammary glands