Sexual Hormones in Humans (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

• Primary sexual characteristics are present during development in the uterus and are the differences in reproductive organs etc between males and females
• Secondary sexual characteristics are the changes that occur during puberty as children become adolescents
• They are controlled by the release of hormones:
  • oestrogen in girls
  • testosterone in boys

 Human secondary sexual characteristics

• Female secondary sexual characteristics:

•  Male secondary sexual characteristics:

• Some changes occur to both boys and girls, including:
  • growth of sexual organs
  • growth of body hair
• Emotional changes also occur due to the increased levels of hormones in the body
  • These include more interest in sex and increased mood swings

• The menstrual cycle starts in early adolescence in girls (around age 12) and is controlled by hormones
• The average menstrual cycle is 28 days long
• Key changes occur in the ovaries and the lining of the uterus
• ovulation occurs about halfway through the cycle (day 14) and the egg then travels down the oviduct to the uterus
• Failure to fertilise the egg causes menstruation (commonly called a period) to occur
  • This is caused by the breakdown of the thickened lining of the uterus
• Menstruation lasts around 5 - 7 days and signals the beginning of the next cycle
• After menstruation finishes, the lining of the uterus starts to thicken again in preparation for possible implantation in the next cycle

Changes in the lining of the uterus during the menstrual cycle are represented graphically. The pink represents the lining getting thicker and thinner; the red lines represent blood vessels.