5.3 Reproduction and Metabolism

• During puberty, reproductive hormones cause secondary sex characteristics to develop
• Ovulation - the release of an egg from the ovary every 28 days
• Testosterone is the main male reproductive hormone and stimulates sperm production
• 4 stages of the menstrual cycle

  1. Menstruation - loss of lining from uterus
  2. Lining starts to thicken
  3. Ovulation (day 14) - egg travels down oviduct to the uterus
  4. Lining is maintained, ready to accept a fertilized egg
• Hormones in the menstrual cycle

  • FSH - matures the follicle, triggers oestrogen release
  • LH - causes ovulation, trigers progesterone release
  • Oestrogen - thickens uterus lining, inhibits FSH, triggers LH release
  • Progesterone - thickens uterus lining, inhibits FSH and LH
• Interactions of hormones in the menstrual cycle

  1. FSH produced by pituitary gland stimulates maturation of egg and follicles.
  2. Ovaries stimulated into producing oestrogen
  3. Oestrogen causes growth of the uterus wall lining, and inhibits FSH
  4. High level of oestrogen stimulates release of LH from pituitary gland
  5. LH stimulates ovulation
  6. Progesterone is produced and maintains the uterus lining, and inhibits FSH and LH
  7. Menstruation - egg not fertilised so uterus lining breaks down, and progesterone drops
• Oral contraceptives

  • Combined (oestrogen and progesterone) - high levels of oestrogen inhibit FSH to prevent maturation and release of eggs, progesterone inhibits mature eggs and stimulates production of thick mucus to prevent sperm from reaching any released eggs
  • Progesterone-only pill - fewer side effects
• Injection, implant, skin patch

  • Slowly release progesterone to inhibit maturation and release of eggs
  • Pros - no need to take pills everyday
• IUD (intrauterine devices)

  • Prevents implantation of an embryo or release a hormone - 2 types
  • Plastic IUD - produces progesterone to stimulate production of a thick mucus lining to prevent sperm reaching eggs
  • Copper IUD - releases low levels of copper ions to disable sperm cells
• Barrier methods of contraceptives prevent the sperm from reaching an egg
• Surgical contraception

  • Males - sperm ducts (tube connecting testes to penis) can be cut and tied in vasectomy
  • Females - fallopian tubes (oviducts connecting ovaries to uterus) cut and tied
• IVF Process

  1. A mother is given FSH and LH to stimulate the maturation of several eggs
  2. The eggs are collected from the mother and fertilised by sperm from the father in the laboratory
  3. The fertilised eggs develop into embryos
  4. At the stage when they are tiny balls of cells, one or two embryos are inserted into the mother's uterus
• Problems with IVF

  • Low success rate
  • Emotionally and physically stressful
  • Can lead to multiple births which are a risk to both babies and mother
• Adrenaline

  • Produced by adrenal glands in times of fear or stress
  • In response to stressful or scary situations, the brain triggers the release of adrenaline from the adrenal glands
  • Adrenaline increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for 'flight or fight'
  • Increased glucose and oxygen are needed by cells for respiration to release more energy for muscles to move
• Thyroxine

  • 2 roles
  • Stimulates basal metabolic rate - speed at which chemical reactions occur in the body when at rest
  • Stimulates protein synthesis in cells, important for growth and development
• Thyroxine in negative feedback

  Too high

  1. TSH is inhibited in the pituitary gland
  2. Less thryoxine is released from the thyroid gland

  Too low

  1. Pituitary gland releases more TSH
  2. Thyroid is stimulated to release more thyroxine
• Conditions in the thyroid gland

  Hyperthyroidism

  • Overactive thyroid gland secreting too much thyroxine into the bloodstream, causing increase in BMR and protein synthesis

  Hypothyroidism

  • Underactive thyroid gland secreting too little thyroxine into the bloodstream, leading to heart and nerve problems, and death