The Menstrual Cycle and Pregnancy (pg. 63)

• The menstrual cycle diagram:

  A) Day 1

  B) Day 4

  C) Day 14

  D) Day 28

  E) Day 4

  F) Stage 1

  G) Lining of the uterus breaks down

  H) Stage 2

  I) Lining of the uterus builds up

  J) Stage 3

  K) Egg released

  L) Stage 4

  M) Lining of the uterus maintained

  N) Next cycle

  
• The menstrual cycle:

  Stage 1. Day 1 - menstruation starts. The uterus lining breaks down for about 4 days.

  Stage 2. The uterus lining builds up again, for day 4 to day 14, into a thick spongy layer full of blood vessels, ready to receive a fertilized egg.

  Stage 3. An egg develops and is released from the ovary at day 14 - this is called ovulation.

  Stage 4. The wall is then maintained for about 14 days until day 28. If no fertilized egg has landed on the uterus wall by day 28, the spongy lining starts to break down and the whole cycle starts again.
• The menstrual cycle is controlled by 4 hormones:

  1. FSH (Follicle-Stimulating Hormone).
  2. Oestrogen.
  3. LH (Luteinizing Hormone).
  4. Progesterone.
• FSH (Follicle-Stimulating Hormone).

  1. Produced in the pituitary gland.
  2. Causes an egg to mature in one of the ovaries, in a structure called a follicle.
  3. Stimulates the ovaries to produce oestrogen.
  4. Oestrogen then inhibits the release of FSH.
• Oestrogen.

  1. Produced in the ovaries.
  2. Causes the lining of the uterus to grow.
  3. Stimulates the release of LH.
• LH (Luteinizing Hormone).

  1. Produced in the pituitary gland.
  2. Stimulates the release of an egg at day 14 (ovulation).
• Progesterone.

  1. Produced in the ovaries by the remains of the follicle after ovulation.
  2. Maintains the lining of the uterus during the second half of the cycle. When the level of progesterone falls, the lining breaks down.
  3. Inhibits the release of LH and FSH.
• Once an ovum has been fertilized, it develops into an embryo and implants in the uterus.
• Once the embryo has been implanted, the placenta develops - this lets the blood of the embryo and mother get very close to allow the exchange of water, food and waste.
• The amnion membrane forms - this surrounds the embryo and is full of amniotic fluid.
• Amniotic fluid protects the embryo against knocks and bumps.
• In later stages of pregnancy, the embryo is called a fetus.
• Pregnancy diagram:

  A) wall of uterus

  B) umbilical cord

  C) placenta

  D) amniotic fluid

  E) developing baby (fetus)

  F) amnion